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From:Roy Lyseng Date:June 17 2011 11:41am
Subject:WL4897: Review comments
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Hi Gleb,

I approve the coding for this worklog.

Please consider the (rather few) suggestions that I have provided inline. They 
should all be tagged with RL: at the front of the line.

=== modified file 'client/mysqltest.cc'
--- client/mysqltest.cc	2011-03-22 15:40:32 +0000
+++ client/mysqltest.cc	2011-06-16 12:58:35 +0000
@@ -201,6 +201,7 @@ static char *opt_plugin_dir= 0;
  static my_regex_t ps_re;     /* the query can be run using PS protocol */
  static my_regex_t sp_re;     /* the query can be run as a SP */
  static my_regex_t view_re;   /* the query can be run as a view*/
+static my_regex_t explain_re;/* the query can be converted to EXPLAIN */

  static void init_re(void);
  static int match_re(my_regex_t *, char *);
@@ -6389,7 +6390,7 @@ static struct my_option my_long_options[
    {"view-protocol", OPT_VIEW_PROTOCOL, "Use views for select.",
     &view_protocol, &view_protocol, 0,
     GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
-  {"explain-protocol", OPT_EXPLAIN_PROTOCOL, "Explains all select.",
+  {"explain-protocol", OPT_EXPLAIN_PROTOCOL, "Explains all select/update/etc.",

RL: Suggestion: "Explain all DML statements"


=== modified file 'sql/CMakeLists.txt'
--- sql/CMakeLists.txt	2011-02-02 08:30:13 +0000
+++ sql/CMakeLists.txt	2011-06-16 12:58:35 +0000
@@ -72,6 +72,7 @@ SET(SQL_SHARED_SOURCES
    mf_iocache.cc
    my_decimal.cc
    net_serv.cc
+  opt_explain.cc
    opt_range.cc
    opt_sum.cc
    parse_file.cc

=== added file 'sql/opt_explain.cc'
--- sql/opt_explain.cc	1970-01-01 00:00:00 +0000
+++ sql/opt_explain.cc	2011-06-16 12:58:35 +0000
@@ -0,0 +1,1541 @@
+/* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */
+
+/** @file "EXPLAIN <command>" implementation */
+
+#include "opt_explain.h"
+#include "sql_select.h"
+#include "sql_partition.h" // for make_used_partitions_str()
+
+static bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit,
+                                select_result *result);
+
+/**
+  A base for all Explain_* classes
+
+  Explain_* classes collect and output EXPLAIN data.
+
+  This class hierarchy is a successor of the old select_describe() function of 5.5.
+*/
+
+class Explain
+{
+private:
+  List<Item> items; ///< item list to feed select_result::send_data()
+  Item_null *nil; ///< pre-allocated NULL item to fill empty columns in EXPLAIN
+
+protected:
+  /**
+    Helper class to keep string data in MEM_ROOT before passing to Item_string
+
+    Since Item_string constructors doesn't copy input string parameter data
+    in the most cases, those input strings must have the same lifetime as
+    Item_string objects, i.e. lifetime of MEM_ROOT.
+    This class allocates input parameters for Item_string objects in MEM_ROOT.
+  */
+  struct mem_root_str
+  {
+    THD * const thd;

RL: Is there a reason to use THD here? A mem_root pointer would probably make 
more sense.

RL: I was told once to write "*const" instead of "* const". It seems to be the 
current practice in e.g. sql_select.cc. But it is up to you.

+    const char *str;
+    size_t length;
+
+    mem_root_str(THD *thd_arg) : thd(thd_arg) { cleanup(); }
+    void cleanup()
+    {
+      str= NULL;
+      length= 0;
+    }

RL: Consider naming this function empty() instead of cleanup(). This name is 
IMHO more describing.

+    bool nil() const { return str == NULL; }

RL: Is is_empty() a more descriptive name than nil()?

+
+    bool set(const char *str_arg)
+    {
+      return set(str_arg, strlen(str_arg));
+    }
+    bool set(const String &s)
+    {
+      return set(s.ptr(), s.length());
+    }
+    /**
+      Make a copy of the string in MEM_ROOT
+
+      @param str_arg    string to copy
+      @param length_arg input string length
+
+      @return false if success, true if error
+    */
+    bool set(const char *str_arg, size_t length_arg)
+    {
+      if (!(str= static_cast<char *>(thd->memdup(str_arg, length_arg))))
+        return true; /* purecov: inspected */
+      length= length_arg;
+      return false;
+    }
+    /**
+      Make a copy of string constant
+
+      Variant of set() usable when the str_arg argument lives longer
+      than the mem_root_str instance.
+    */
+    void set_const(const char *str_arg)
+    {
+      str= str_arg;
+      length= strlen(str_arg);
+    }
+  };
+
+  /*
+    Next "col_*" fields are intended for the filling by "explain_*()" methods.

RL: The following "col_*" fields are intended to be filled by "explain_*()" 
functions.

+    Then the make_list() method links these Items into "items" list.

RL: method -> function. This is applicable several places.
+
+    NOTE: NULL value or mem_root_str.nil()==true means that Item_null object
+          will be pushed into "items" list instead.
+  */
+  Item_uint   *col_id; ///< "id" column: seq. number of SELECT withing the query
+  mem_root_str col_select_type; ///< "select_type" column
+  mem_root_str col_table_name; ///< "table" to which the row of output refers
+  mem_root_str col_partitions; ///< "partitions" column
+  mem_root_str col_join_type; ///< "type" column, see join_type_str array
+  mem_root_str col_possible_keys; ///< "possible_keys": comma-separated list
+  mem_root_str col_key; ///< "key" column: index that is actually decided to use
+  mem_root_str col_key_len; ///< "key_length" column: length of the "key" above
+  mem_root_str col_ref; ///< "ref":columns/constants which are compared to "key"
+  Item_int    *col_rows; ///< "rows": estimated number of examined table rows
+  Item_float  *col_filtered; ///< "filtered": % of rows filtered by condition
+  mem_root_str col_extra; ///< "extra" column: additional information
+
+  THD * const thd; ///< cached THD pointer
+  const CHARSET_INFO * const cs; ///< cached pointer to system_charset_info
+  JOIN * const join; ///< top-level JOIN (if any) provided by caller
+
+  select_result * const external_result; ///< stream (if any) provided by caller
+
+protected:
+  explicit Explain(THD *thd_arg, JOIN *join_arg= NULL)
+  : nil(NULL),
+    col_select_type(thd_arg),
+    col_table_name(thd_arg),
+    col_partitions(thd_arg),
+    col_join_type(thd_arg),
+    col_possible_keys(thd_arg),
+    col_key(thd_arg),
+    col_key_len(thd_arg),
+    col_ref(thd_arg),
+    col_extra(thd_arg),
+    thd(thd_arg),
+    cs(system_charset_info),
+    join(join_arg),
+    external_result(join ? join->result : NULL)
+  {
+    init_columns();
+  }
+  virtual ~Explain() {}
+
+public:
+  bool send();
+
+private:
+  void init_columns();
+  bool make_list();
+  bool push(Item *item) { return items.push_back(item ? item : nil); }
+  bool push(const mem_root_str &s)
+  {
+    if (s.nil())
+      return items.push_back(nil);
+    Item_string *item= new Item_string(s.str, s.length, cs);
+    return item == NULL || items.push_back(item);
+  }
+
+protected:
+  bool describe(uint8 mask) { return thd->lex->describe & mask; }
+
+  SELECT_LEX *select_lex() const
+  {
+    return join ? join->select_lex : &thd->lex->select_lex;
+  }
+
+  /**
+    Prepare the self-allocated result object
+
+    For queries with top-level JOIN the caller provides pre-allocated
+    select_send object. Then that JOIN object prepares the select_send
+    object calling result->prepare() in JOIN::prepare(),
+    result->initalize_tables() in JOIN::optimize() and result->prepare2()
+    in JOIN::exec().
+    However without the presence of the top-level JOIN we have to
+    prepare/initialize select_send object manually.
+  */
+  bool prepare(select_result *result)
+  {
+    DBUG_ASSERT(join == NULL);
+    List<Item> dummy;
+    return result->prepare(dummy, select_lex()->master_unit()) ||
+           result->prepare2();
+  }
+
+  virtual bool send_to(select_result *to);
+
+  /*
+    Rest of the methods are overloadable functions, those calculate and fill
+    "col_*" fields with Items for further sending as EXPLAIN columns.
+
+    "explain_*" methods return false on success and true on error (usually OOM).
+  */
+  virtual bool explain_id();
+  virtual bool explain_select_type();
+  virtual bool explain_table_name() { return false; }
+  virtual bool explain_partitions() { return false; }
+  virtual bool explain_join_type() { return false; }
+  virtual bool explain_possible_keys() { return false; }
+  /** fill col_key and and col_key_len fields together */
+  virtual bool explain_key_and_len() { return false; }
+  virtual bool explain_ref() { return false; }
+  /** fill col_rows and col_filtered fields together */
+  virtual bool explain_rows_and_filtered() { return false; }
+  virtual bool explain_extra();
+};
+
+
+/**
+  Explain_no_table class outputs a trivial EXPLAIN row with "extra" column
+
+  This class is intended for simple cases to produce EXPLAIN output
+  with "No tables used", "No matching records" etc.
+  Optionally it can output number of estimated rows in the "row"
+  column.
+
+  @note This class also produces EXPLAIN rows for inner units (if any).
+*/
+
+class Explain_no_table: public Explain
+{
+private:
+  const char *message; ///< cached "message" argument
+  const ha_rows rows; ///< HA_POS_ERROR or cached "rows" argument
+
+public:
+  Explain_no_table(THD *thd_arg, JOIN *join_arg, const char *message_arg)
+  : Explain(thd_arg, join_arg), message(message_arg), rows(HA_POS_ERROR)
+  {}
+
+  Explain_no_table(THD *thd_arg, const char *message_arg,
+                   ha_rows rows_arg= HA_POS_ERROR)
+  : Explain(thd_arg), message(message_arg), rows(rows_arg)
+  {}
+
+protected:
+  virtual bool explain_rows_and_filtered();
+  virtual bool explain_extra();
+};
+
+
+/**
+  Explain_union class outputs EXPLAIN row for UNION
+*/
+
+class Explain_union : public Explain
+{
+public:
+  Explain_union(THD *thd_arg, JOIN *join_arg) : Explain(thd_arg, join_arg)
+  {
+    /* it's a UNION: */
+    DBUG_ASSERT(join_arg->select_lex == join_arg->unit->fake_select_lex);
+  }
+
+protected:
+  virtual bool explain_id();
+  virtual bool explain_table_name();
+  virtual bool explain_join_type();
+  virtual bool explain_extra();
+};
+
+
+
+/**
+  Common base class for Explain_join and Explain_table
+*/
+
+class Explain_table_base : public Explain {
+protected:
+  const TABLE *table;
+  key_map usable_keys;
+
+  Explain_table_base(THD * const thd_arg, JOIN * const join_arg)
+  : Explain(thd_arg, join_arg), table(NULL)
+  {}
+
+  Explain_table_base(THD * const thd_arg, TABLE * const table_arg)
+  : Explain(thd_arg), table(table_arg)
+  {}
+
+  virtual bool explain_partitions();
+  virtual bool explain_possible_keys();
+
+  bool explain_key_and_len_quick(const SQL_SELECT *select);
+  bool explain_key_and_len_index(int key);
+  bool explain_key_and_len_index(int key, uint key_length);
+  void explain_extra_common(const SQL_SELECT *select,
+                            const JOIN_TAB *tab,
+                            int quick_type,
+                            uint keyno,
+                            bool need_tmp_table,
+                            bool need_sort,
+                            String *str_extra);
+};
+
+
+/**
+  Explain_join class produces EXPLAIN output for JOINs
+*/
+
+class Explain_join : public Explain_table_base
+{
+private:
+  const bool need_tmp_table; ///< add "Using temporary" to "extra" if true
+  const bool need_order; ///< add "Using filesort"" to "extra" if true
+  const bool distinct; ///< add "Distinct" string to "extra" column if true
+
+  uint tabnum; ///< current tab number in join->join_tab[]
+  JOIN_TAB *tab; ///< current JOIN_TAB
+  int quick_type; ///< current quick type, see anon. enum at QUICK_SELECT_I
+  table_map used_tables; ///< accumulate used tables bitmap
+  uint last_sjm_table; ///< last materialized semi-joined table
+
+public:
+  Explain_join(THD *thd_arg, JOIN *join_arg,
+               bool need_tmp_table_arg, bool need_order_arg,
+               bool distinct_arg)
+  : Explain_table_base(thd_arg, join_arg), need_tmp_table(need_tmp_table_arg),
+    need_order(need_order_arg), distinct(distinct_arg),
+    tabnum(0), used_tables(0), last_sjm_table(MAX_TABLES)
+  {
+    /* it is not UNION: */
+    DBUG_ASSERT(join_arg->select_lex != join_arg->unit->fake_select_lex);
+  }
+
+protected:
+  virtual bool send_to(select_result *to);
+  virtual bool explain_table_name();
+  virtual bool explain_join_type();
+  virtual bool explain_key_and_len();
+  virtual bool explain_ref();
+  virtual bool explain_rows_and_filtered();
+  virtual bool explain_extra();
+};
+
+
+/**
+  Explain_table class produce EXPLAIN output for queries without top-level JOIN
+
+  This class is a simplified version of the Explain_join class. It works in the
+  context of queries which implementation lacks top-level JOIN object (EXPLAIN
+  single-table UPDATE and DELETE).
+*/
+
+class Explain_table: public Explain_table_base
+{
+private:
+  const SQL_SELECT * const select; ///< cached "select" argument
+  const uint       key;        ///< cached "key" number argument
+  const ha_rows    limit;      ///< HA_POS_ERROR or cached "limit" argument
+  const bool       need_tmp_table; ///< cached need_tmp_table argument
+  const bool       need_sort;  ///< cached need_sort argument
+
+public:
+  Explain_table(THD * const thd_arg, TABLE * const table_arg,
+                const SQL_SELECT *select_arg,
+                uint key_arg, ha_rows limit_arg,
+                bool need_tmp_table_arg, bool need_sort_arg)
+  : Explain_table_base(thd_arg, table_arg), select(select_arg), key(key_arg),
+    limit(limit_arg),
+    need_tmp_table(need_tmp_table_arg), need_sort(need_sort_arg)
+  {
+    usable_keys= table->keys_in_use_for_query;
+  }
+
+private:
+  virtual bool explain_table_name();
+  virtual bool explain_join_type();
+  virtual bool explain_key_and_len();
+  virtual bool explain_rows_and_filtered();
+  virtual bool explain_extra();
+};
+
+
+static join_type calc_join_type(int quick_type)
+{
+  if ((quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE) ||
+      (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT) ||
+      (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION))
+    return JT_INDEX_MERGE;
+  else
+    return JT_RANGE;
+}
+
+
+/* Explain class functions ****************************************************/
+
+
+/**
+  Explain class main function
+
+  This method:
+    a) allocates a select_send object (if no one pre-allocated available),
+    b) calculates and sends whole EXPLAIN data.
+
+  @return false if success, true if error
+*/
+
+bool Explain::send()
+{
+  DBUG_ENTER("Explain::send");
+  /* Don't log this into the slow query log */
+  thd->server_status&= ~(SERVER_QUERY_NO_INDEX_USED |
+                         SERVER_QUERY_NO_GOOD_INDEX_USED);
+
+  select_result *result;
+  if (external_result == NULL)
+  {
+    /* Create select_result object if the called doesn't provide one: */

RL: called -> caller

+    if (!(result= new select_send))
+      DBUG_RETURN(true); /* purecov: inspected */
+    if (thd->send_explain_fields(result) || prepare(result))
+    {
+      delete result;
+      DBUG_RETURN(true); /* purecov: inspected */
+    }
+  }
+  else
+  {
+    result= external_result;
+    external_result->reset_offset_limit_cnt();
+  }
+
+  if (nil == NULL && !(nil= new Item_null))
+    DBUG_RETURN(true); /* purecov: inspected */
+  bool ret= send_to(result);
+
+  if (ret && join)
+    join->error= 1; /* purecov: inspected */
+
+  for (SELECT_LEX_UNIT *unit= select_lex()->first_inner_unit();
+       unit && !ret;
+       unit= unit->next_unit())
+    ret= mysql_explain_union(thd, unit, result);
+
+  if (external_result == NULL)
+  {
+    if (ret)
+      result->abort_result_set(); /* purecov: inspected */
+    else
+      result->send_eof();
+    delete result;
+  }
+  DBUG_RETURN(ret);
+}
+
+
+/**
+  Reset all "col_*" fields
+*/
+
+void Explain::init_columns()
+{
+  col_id= NULL;
+  col_select_type.cleanup();
+  col_table_name.cleanup();
+  col_partitions.cleanup();
+  col_join_type.cleanup();
+  col_possible_keys.cleanup();
+  col_key.cleanup();
+  col_key_len.cleanup();
+  col_ref.cleanup();
+  col_rows= NULL;
+  col_filtered= NULL;
+  col_extra.cleanup();
+}
+
+
+/**
+  Calculate EXPLAIN column values and link them into "items" list
+
+  @return false if success, true if error
+*/
+
+bool Explain::make_list()
+{
+  if (explain_id() ||
+      explain_select_type() ||
+      explain_table_name() ||
+      explain_partitions() ||
+      explain_join_type() ||
+      explain_possible_keys() ||
+      explain_key_and_len() ||
+      explain_ref() ||
+      explain_rows_and_filtered() ||
+      explain_extra())
+    return true; /* purecov: inspected */
+
+  /*
+    NOTE: the number/types of items pushed into item_list must be in sync with
+    EXPLAIN column types as they're "defined" in THD::send_explain_fields()
+  */
+  return push(col_id) ||
+         push(col_select_type) ||
+         push(col_table_name) ||
+         (describe(DESCRIBE_PARTITIONS) && push(col_partitions)) ||
+         push(col_join_type) ||
+         push(col_possible_keys) ||
+         push(col_key) ||
+         push(col_key_len) ||
+         push(col_ref) ||
+         push(col_rows) ||
+         (describe(DESCRIBE_EXTENDED) && push(col_filtered)) ||
+         push(col_extra);
+}
+
+
+/**
+  Make "items" list and send it to select_result output stream
+
+  @note An overloaded Explain_join::send_to() function sends
+        one item list per each JOIN::join_tab[] element.
+
+  @return false if success, true if error
+*/
+
+bool Explain::send_to(select_result *to)
+{
+  const bool ret= make_list() || to->send_data(items);
+  items.empty();
+  init_columns();
+  return ret;
+}
+
+
+bool Explain::explain_id()
+{
+  col_id= new Item_uint(select_lex()->select_number);
+  return col_id == NULL;
+}
+
+
+bool Explain::explain_select_type()
+{
+  if (select_lex()->type)
+    col_select_type.set(select_lex()->type);
+  else if (select_lex()->first_inner_unit() || select_lex()->next_select())
+    col_select_type.set_const("PRIMARY");
+  else
+    col_select_type.set_const("SIMPLE");
+  return col_select_type.nil();
+}
+
+
+bool Explain::explain_extra()
+{
+  col_extra.set_const("");
+  return false;
+}
+
+
+/* Explain_no_table class functions *******************************************/
+
+
+bool Explain_no_table::explain_rows_and_filtered()
+{
+  if (rows == HA_POS_ERROR)
+    return false;
+  col_rows= new Item_int(rows, MY_INT64_NUM_DECIMAL_DIGITS);
+  return col_rows == NULL;
+}
+
+
+bool Explain_no_table::explain_extra()
+{
+  return col_extra.set(message);
+}
+
+
+/* Explain_union class functions **********************************************/
+
+
+bool Explain_union::explain_id()
+{
+  return false;
+}
+
+
+bool Explain_union::explain_table_name()
+{
+  SELECT_LEX *last_select= join->unit->first_select()->last_select();
+  // # characters needed to print select_number of last select
+  int last_length= (int)log10((double)last_select->select_number)+1;
+
+  SELECT_LEX *sl= join->unit->first_select();
+  uint len= 6, lastop= 0;
+  char table_name_buffer[NAME_LEN];
+  memcpy(table_name_buffer, STRING_WITH_LEN("<union"));
+  /*
+    - len + lastop: current position in table_name_buffer
+    - 6 + last_length: the number of characters needed to print
+      '...,'<last_select->select_number>'>\0'
+  */
+  for (;
+       sl && len + lastop + 6 + last_length < NAME_CHAR_LEN;
+       sl= sl->next_select())
+  {
+    len+= lastop;
+    lastop= my_snprintf(table_name_buffer + len, NAME_CHAR_LEN - len,
+                        "%u,", sl->select_number);
+  }
+  if (sl || len + lastop >= NAME_CHAR_LEN)
+  {
+    memcpy(table_name_buffer + len, STRING_WITH_LEN("...,"));
+    len+= 4;
+    lastop= my_snprintf(table_name_buffer + len, NAME_CHAR_LEN - len,
+                        "%u,", last_select->select_number);
+  }
+  len+= lastop;
+  table_name_buffer[len - 1]= '>';  // change ',' to '>'
+
+  return col_table_name.set(table_name_buffer, len);
+}
+
+
+bool Explain_union::explain_join_type()
+{
+  col_join_type.set_const(join_type_str[JT_ALL]);
+  return false;
+}
+
+
+bool Explain_union::explain_extra()
+{
+  /*
+    here we assume that the query will return at least two rows, so we
+    show "filesort" in EXPLAIN. Of course, sometimes we'll be wrong
+    and no filesort will be actually done, but executing all selects in
+    the UNION to provide precise EXPLAIN information will hardly be
+    appreciated :)
+  */
+  if (join->unit->global_parameters->order_list.first)
+  {
+    col_extra.set_const("Using filesort");
+    return false;
+  }
+  return Explain::explain_extra();
+}
+
+
+/* Explain_table_base class functions *****************************************/
+
+
+bool Explain_table_base::explain_partitions()
+{
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+  if (!table->derived_select_number && table->part_info)
+  {
+    String s;
+    make_used_partitions_str(table->part_info, &s);
+    return col_partitions.set(s);
+  }
+#endif
+  return false;
+}
+
+
+bool Explain_table_base::explain_possible_keys()
+{
+  if (usable_keys.is_clear_all())
+    return false;
+
+  StringBuff<512> str_possible_keys(cs);
+
+  for (uint j= 0 ; j < table->s->keys ; j++)
+  {
+    if (usable_keys.is_set(j))
+    {
+      if (str_possible_keys.length())
+        str_possible_keys.append(',');
+      str_possible_keys.append(table->key_info[j].name,
+                               strlen(table->key_info[j].name), cs);
+    }
+  }
+  if (str_possible_keys.length())
+    return col_possible_keys.set(str_possible_keys);
+  return false;
+}
+
+
+bool Explain_table_base::explain_key_and_len_quick(const SQL_SELECT *select)
+{
+  DBUG_ASSERT(select && select->quick);
+
+  StringBuff<512> str_key(cs);
+  StringBuff<512> str_key_len(cs);
+
+  select->quick->add_keys_and_lengths(&str_key, &str_key_len);
+  return col_key.set(str_key) || col_key_len.set(str_key_len);
+}
+
+
+bool Explain_table_base::explain_key_and_len_index(int key)
+{
+  DBUG_ASSERT(key != MAX_KEY);
+  return explain_key_and_len_index(key, table->key_info[key].key_length);
+}
+
+
+bool Explain_table_base::explain_key_and_len_index(int key, uint key_length)
+{
+  DBUG_ASSERT(key != MAX_KEY);
+
+  const KEY *key_info= table->key_info + key;
+  char buff_key_len[24];
+  const int length= longlong2str(key_length, buff_key_len, 10) - buff_key_len;
+  return col_key.set(key_info->name) || col_key_len.set(buff_key_len, length);
+}
+
+
+void Explain_table_base::explain_extra_common(const SQL_SELECT *select,
+                                              const JOIN_TAB *tab,
+                                              int quick_type,
+                                              uint keyno,
+                                              bool need_tmp_table,
+                                              bool need_sort,
+                                              String *str_extra)
+{
+  if ((keyno != MAX_KEY && keyno == table->file->pushed_idx_cond_keyno
&&
+       table->file->pushed_idx_cond) || (tab && tab->cache_idx_cond))
+    str_extra->append(STRING_WITH_LEN("; Using index condition"));
+
+  switch (quick_type) {
+  case QUICK_SELECT_I::QS_TYPE_ROR_UNION:
+  case QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT:
+  case QUICK_SELECT_I::QS_TYPE_INDEX_MERGE:
+    str_extra->append(STRING_WITH_LEN("; Using "));
+    select->quick->add_info_string(str_extra);
+    break;
+  default: ;
+  }
+
+  if (select)
+  {
+    if (tab && tab->use_quick == QS_DYNAMIC_RANGE)
+    {
+      /* 4 bits per 1 hex digit + terminating '\0' */
+      char buf[MAX_KEY / 4 + 1];
+      str_extra->append(STRING_WITH_LEN("; Range checked for each "
+                                        "record (index map: 0x"));
+      str_extra->append(tab->keys.print(buf));
+      str_extra->append(')');
+    }
+    else if (select->cond)
+    {
+      const Item *pushed_cond= table->file->pushed_cond;
+
+      if (thd->optimizer_switch_flag(OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN)
&&
+          pushed_cond)
+      {
+        str_extra->append(STRING_WITH_LEN("; Using where with pushed condition"));
+        if (describe(DESCRIBE_EXTENDED))
+        {
+          str_extra->append(STRING_WITH_LEN(": "));
+          ((Item *)pushed_cond)->print(str_extra, QT_ORDINARY);
+        }
+      }
+      else
+        str_extra->append(STRING_WITH_LEN("; Using where"));
+    }
+  }
+  if (table->reginfo.not_exists_optimize)
+    str_extra->append(STRING_WITH_LEN("; Not exists"));
+
+  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE &&
+      !(((QUICK_RANGE_SELECT*)(select->quick))->mrr_flags &
+       (HA_MRR_USE_DEFAULT_IMPL | HA_MRR_SORTED)))
+  {
+    /*
+      During normal execution of a query, multi_range_read_init() is
+      called to initialize MRR. If HA_MRR_SORTED is set at this point,
+      multi_range_read_init() for any native MRR implementation will
+      revert to default MRR because they cannot produce sorted output
+      currently.
+      Calling multi_range_read_init() can potentially be costly, so it
+      is not done when executing an EXPLAIN. We therefore make the
+      assumption that HA_MRR_SORTED means no MRR. If some MRR native
+      implementation will support sorted output in the future, a
+      function "bool mrr_supports_sorted()" should be added in the
+      handler.
+    */
+    str_extra->append(STRING_WITH_LEN("; Using MRR"));
+  }
+  if (need_sort)
+    str_extra->append(STRING_WITH_LEN("; Using filesort"));
+  if (need_tmp_table)
+    str_extra->append(STRING_WITH_LEN("; Using temporary"));
+}
+
+
+/* Explain_join class functions ***********************************************/
+
+
+bool Explain_join::send_to(select_result *to)
+{
+  for (; tabnum < join->tables; tabnum++)
+  {
+    tab= join->join_tab + tabnum;
+    table= tab->table;
+    usable_keys= tab->keys;
+    quick_type= -1;
+
+    if (tab->type == JT_ALL && tab->select &&
tab->select->quick)
+    {
+      quick_type= tab->select->quick->get_type();
+      tab->type= calc_join_type(quick_type);
+    }
+
+    if (Explain_table_base::send_to(external_result))
+      return true; /* purecov: inspected */
+
+    used_tables|= table->map;
+  }
+  return false;
+}
+
+
+bool Explain_join::explain_table_name()
+{
+  if (table->derived_select_number)
+  {
+    /* Derived table name generation */
+    char table_name_buffer[NAME_LEN];
+    const size_t len= my_snprintf(table_name_buffer,
+                                  sizeof(table_name_buffer) - 1,
+                                  "<derived%u>", table->derived_select_number);
+    return col_table_name.set(table_name_buffer, len);
+  }
+  else
+    return col_table_name.set(table->pos_in_table_list->alias);
+}
+
+
+bool Explain_join::explain_join_type()
+{
+  col_join_type.set_const(join_type_str[tab->type]);
+  return false;
+}
+
+
+bool Explain_join::explain_key_and_len()
+{
+  if (tab->ref.key_parts)
+    return explain_key_and_len_index(tab->ref.key, tab->ref.key_length);
+  else if (tab->type == JT_NEXT)
+    return explain_key_and_len_index(tab->index);
+  else if (tab->select && tab->select->quick)
+    return explain_key_and_len_quick(tab->select);
+  else
+  {
+    const TABLE_LIST *table_list= table->pos_in_table_list;
+    if (table_list->schema_table &&
+        table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
+    {
+      StringBuff<512> str_key(cs);
+      const char *f_name;
+      int f_idx;
+      if (table_list->has_db_lookup_value)
+      {
+        f_idx= table_list->schema_table->idx_field1;
+        f_name= table_list->schema_table->fields_info[f_idx].field_name;
+        str_key.append(f_name, strlen(f_name), cs);
+      }
+      if (table_list->has_table_lookup_value)
+      {
+        if (table_list->has_db_lookup_value)
+          str_key.append(',');
+        f_idx= table_list->schema_table->idx_field2;
+        f_name= table_list->schema_table->fields_info[f_idx].field_name;
+        str_key.append(f_name, strlen(f_name), cs);
+      }
+      if (str_key.length())
+        return col_key.set(str_key);
+    }
+  }
+  return false;
+}
+
+
+bool Explain_join::explain_ref()
+{
+  if (tab->ref.key_parts)
+  {
+    StringBuff<512> str_ref(cs);
+    for (const store_key * const *ref= tab->ref.key_copy; *ref; ref++)
+    {
+      if (str_ref.length())
+        str_ref.append(',');
+      str_ref.append((*ref)->name(), strlen((*ref)->name()), cs);
+    }
+    return col_ref.set(str_ref);
+  }
+  return false;
+}
+
+
+bool Explain_join::explain_rows_and_filtered()
+{
+  if (table->pos_in_table_list->schema_table)
+    return false;
+
+  double examined_rows;
+  if (tab->select && tab->select->quick)
+    examined_rows= rows2double(tab->select->quick->records);
+  else if (tab->type == JT_NEXT || tab->type == JT_ALL)
+  {
+    if (tab->limit)
+      examined_rows= rows2double(tab->limit);
+    else
+    {
+      table->file->info(HA_STATUS_VARIABLE);
+      examined_rows= rows2double(table->file->stats.records);
+    }
+  }
+  else
+    examined_rows= join->best_positions[tabnum].records_read;
+
+  col_rows= new Item_int((longlong) (ulonglong) examined_rows,
+                         MY_INT64_NUM_DECIMAL_DIGITS);
+  if (col_rows == NULL)
+    return true; /* purecov: inspected */
+
+  /* Add "filtered" field */
+  if (describe(DESCRIBE_EXTENDED))
+  {
+    float f= 0.0;
+    if (examined_rows)
+      f= 100.0 * join->best_positions[tabnum].records_read / examined_rows;
+    col_filtered= new Item_float(f, 2);
+    return col_filtered == NULL;
+  }
+  return false;
+}
+
+
+bool Explain_join::explain_extra()
+{
+  StringBuff<512> str_extra(cs);
+
+  if (tab->info)
+    col_extra.set(tab->info);
+  else if (tab->packed_info & TAB_INFO_HAVE_VALUE)
+  {
+    if (tab->packed_info & TAB_INFO_USING_INDEX)
+      str_extra.append(STRING_WITH_LEN("; Using index"));
+    if (tab->packed_info & TAB_INFO_USING_WHERE)
+      str_extra.append(STRING_WITH_LEN("; Using where"));
+    if (tab->packed_info & TAB_INFO_FULL_SCAN_ON_NULL)
+      str_extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
+    /* Skip initial "; "*/
+    const char *str= str_extra.ptr();
+    uint32 len= str_extra.length();
+    if (len)
+    {
+      str += 2;
+      len -= 2;
+    }
+    col_extra.set(str, len);
+  }
+  else
+  {
+    const SQL_SELECT *select= tab->select;
+    uint keyno= MAX_KEY;
+    if (tab->ref.key_parts)
+      keyno= tab->ref.key;
+    else if (select && select->quick)
+      keyno = select->quick->index;
+
+    explain_extra_common(select, tab, quick_type, keyno,
+                         (tabnum == 0 && need_tmp_table),
+                         (tabnum == 0 && need_order),
+                         &str_extra);
+
+    const TABLE_LIST *table_list= table->pos_in_table_list;
+    if (table_list->schema_table &&
+        table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
+    {
+      if (!table_list->table_open_method)
+        str_extra.append(STRING_WITH_LEN("; Skip_open_table"));
+      else if (table_list->table_open_method == OPEN_FRM_ONLY)
+        str_extra.append(STRING_WITH_LEN("; Open_frm_only"));
+      else
+        str_extra.append(STRING_WITH_LEN("; Open_full_table"));
+      if (table_list->has_db_lookup_value &&
+          table_list->has_table_lookup_value)
+        str_extra.append(STRING_WITH_LEN("; Scanned 0 databases"));
+      else if (table_list->has_db_lookup_value ||
+               table_list->has_table_lookup_value)
+        str_extra.append(STRING_WITH_LEN("; Scanned 1 database"));
+      else
+        str_extra.append(STRING_WITH_LEN("; Scanned all databases"));
+    }
+    if (((tab->type == JT_NEXT || tab->type == JT_CONST) &&
+         table->covering_keys.is_set(tab->index)) ||
+        (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT &&
+         !((QUICK_ROR_INTERSECT_SELECT*) select->quick)->need_to_fetch_row) ||
+        table->key_read)
+    {
+      if (quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+      {
+        QUICK_GROUP_MIN_MAX_SELECT *qgs=
+          (QUICK_GROUP_MIN_MAX_SELECT *) select->quick;
+        str_extra.append(STRING_WITH_LEN("; Using index for group-by"));
+        qgs->append_loose_scan_type(&str_extra);
+      }
+      else
+        str_extra.append(STRING_WITH_LEN("; Using index"));
+    }
+
+    if (distinct && test_all_bits(used_tables,thd->used_tables))
+      str_extra.append(STRING_WITH_LEN("; Distinct"));
+
+    if (tab->loosescan_match_tab)
+      str_extra.append(STRING_WITH_LEN("; LooseScan"));
+
+    if (tab->flush_weedout_table)
+      str_extra.append(STRING_WITH_LEN("; Start temporary"));
+    if (tab->check_weed_out_table)
+      str_extra.append(STRING_WITH_LEN("; End temporary"));
+    else if (tab->do_firstmatch)
+    {
+      if (tab->do_firstmatch == join->join_tab - 1)
+        str_extra.append(STRING_WITH_LEN("; FirstMatch"));
+      else
+      {
+        str_extra.append(STRING_WITH_LEN("; FirstMatch("));
+        TABLE *prev_table= tab->do_firstmatch->table;
+        if (prev_table->derived_select_number)
+        {
+          char namebuf[NAME_LEN];
+          /* Derived table name generation */
+          int len= my_snprintf(namebuf, sizeof(namebuf)-1,
+                               "<derived%u>",
+                               prev_table->derived_select_number);
+          str_extra.append(namebuf, len);
+        }
+        else
+          str_extra.append(prev_table->pos_in_table_list->alias);
+        str_extra.append(STRING_WITH_LEN(")"));
+      }
+    }
+    uint sj_strategy= join->best_positions[tabnum].sj_strategy;
+    if (sj_is_materialize_strategy(sj_strategy))
+    {
+      if (join->best_positions[tabnum].n_sj_tables == 1)
+        str_extra.append(STRING_WITH_LEN("; Materialize"));
+      else
+      {
+        last_sjm_table= tabnum + join->best_positions[tabnum].n_sj_tables - 1;
+        str_extra.append(STRING_WITH_LEN("; Start materialize"));
+      }
+      if (sj_strategy == SJ_OPT_MATERIALIZE_SCAN)
+          str_extra.append(STRING_WITH_LEN("; Scan"));
+    }
+    else if (last_sjm_table == tabnum)
+    {
+      str_extra.append(STRING_WITH_LEN("; End materialize"));
+    }
+
+    for (uint part= 0; part < tab->ref.key_parts; part++)
+    {
+      if (tab->ref.cond_guards[part])
+      {
+        str_extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
+        break;
+      }
+    }
+
+    if (tabnum > 0 && tab[-1].next_select == sub_select_cache)
+    {
+      str_extra.append(STRING_WITH_LEN("; Using join buffer ("));
+      if ((tab->use_join_cache & JOIN_CACHE::ALG_BNL))
+        str_extra.append(STRING_WITH_LEN("BNL"));
+      else if ((tab->use_join_cache & JOIN_CACHE::ALG_BKA))
+        str_extra.append(STRING_WITH_LEN("BKA"));
+      else if ((tab->use_join_cache & JOIN_CACHE::ALG_BKA_UNIQUE))
+        str_extra.append(STRING_WITH_LEN("BKA_UNIQUE"));
+      else
+        DBUG_ASSERT(0); /* purecov: inspected */
+      if (tab->use_join_cache & JOIN_CACHE::NON_INCREMENTAL_BUFFER)
+        str_extra.append(STRING_WITH_LEN(", regular buffers)"));
+      else
+        str_extra.append(STRING_WITH_LEN(", incremental buffers)"));
+    }
+
+    /* Skip initial "; "*/
+    const char *str= str_extra.ptr();
+    uint32 len= str_extra.length();
+    if (len)
+    {
+      str += 2;
+      len -= 2;
+    }
+    col_extra.set(str, len);
+  }
+  return col_extra.nil();
+}
+
+
+/* Explain_table class functions **********************************************/
+
+
+bool Explain_table::explain_table_name()
+{
+  return col_table_name.set(table->alias);
+}
+
+
+bool Explain_table::explain_join_type()
+{
+  join_type jt;
+  if (select && select->quick)
+    jt= calc_join_type(select->quick->get_type());
+  else
+    jt= JT_ALL;
+
+  col_join_type.set_const(join_type_str[jt]);
+  return false;
+}
+
+
+bool Explain_table::explain_key_and_len()
+{
+  if (key != MAX_KEY)
+    return explain_key_and_len_index(key);
+  if (select && select->quick)
+    return explain_key_and_len_quick(select);
+  return false;
+}
+
+
+bool Explain_table::explain_rows_and_filtered()
+{
+  double examined_rows;
+  if (select && select->quick)
+    examined_rows= rows2double(select->quick->records);
+  else if (!select && !need_sort && limit != HA_POS_ERROR)
+    examined_rows= rows2double(limit);
+  else
+  {
+    table->file->info(HA_STATUS_VARIABLE);
+    examined_rows= rows2double(table->file->stats.records);
+  }
+  col_rows= new Item_int((longlong) (ulonglong) examined_rows,
+                         MY_INT64_NUM_DECIMAL_DIGITS);
+  if (col_rows == NULL)
+    return true; /* purecov: inspected */
+
+  if (describe(DESCRIBE_EXTENDED))
+  {
+    col_filtered= new Item_float(100.0, 2);
+    if (col_filtered == NULL)
+      return true; /* purecov: inspected */
+  }
+  return false;
+}
+
+
+bool Explain_table::explain_extra()
+{
+  StringBuff<512> str_extra(cs);
+  const uint keyno= (select && select->quick) ? select->quick->index :
key;
+  const int quick_type= (select && select->quick) ?
select->quick->get_type()
+                                                  : -1;
+  explain_extra_common(select, NULL, quick_type, keyno, need_tmp_table,
+                       need_sort, &str_extra);
+
+  /* Skip initial "; "*/
+  const char *str= str_extra.ptr();
+  uint32 len= str_extra.length();
+  if (len)
+  {
+    str += 2;
+    len -= 2;
+  }
+  return col_extra.set(str, len);
+}
+
+
+/**
+  EXPLAIN functionality for insert_select, multi_update and multi_delete
+
+  This class objects substitute insert_select, multi_update and multi_delete
+  data interceptor objects to implement EXPLAIN for INSERT, REPLACE and
+  multi-table UPDATE and DELETE queries.
+  explain_send class object initializes tables like insert_select, multi_update
+  or multi_delete data interceptor do, but it suppress table data modification
+  by the underlying interceptor object.
+  Thus, we can use explain_send object in the context of EXPLAIN INSERT/
+  REPLACE/UPDATE/DELETE query like we use select_send in the context of
+  EXPLAIN SELECT command:
+    1) in presence of lex->describe flag we pass explain_send object to the
+       mysql_select() function,
+    2) it call prepare(), prepare2() and initialize_tables() methods to
+       mark modified tables etc.
+
+*/
+
+class explain_send : public select_send {
+protected:
+  /*
+    As far as we use explain_send object in a place of select_send, explain_send
+    have to pass multiple invocation of its prepare(), prepare2() and
+    initialize_tables() methods, since JOIN::exec() of subqueries runs
+    these methods of select_send multiple times by design.
+    insert_select, multi_update and multi_delete class methods are not intended
+    for multiple invocations, so "prepared", "prepared2" and "initialized" flags
+    guard data interceptor object from method re-invocation.
+  */
+  bool prepared;    ///< prepare() is done
+  bool prepared2;   ///< prepare2() is done
+  bool initialized; ///< initialize_tables() is done
+
+  /**
+    Pointer to underlying insert_select, multi_update or multi_delete object
+  */
+  select_result_interceptor *interceptor;
+
+public:
+  explain_send(select_result_interceptor *interceptor_arg)
+  : prepared(false), prepared2(false), initialized(false),
+    interceptor(interceptor_arg)
+  {}
+
+protected:
+  virtual int prepare(List<Item> &list, SELECT_LEX_UNIT *u)
+  {
+    if (prepared)
+      return false;
+    prepared= true;
+    return select_send::prepare(list, u) || interceptor->prepare(list, u);
+  }
+
+  virtual int prepare2(void)
+  {
+    if (prepared2)
+      return false;
+    prepared2= true;
+    return select_send::prepare2() || interceptor->prepare2();
+  }
+
+  virtual bool initialize_tables(JOIN *join)
+  {
+    if (initialized)
+      return false;
+    initialized= true;
+    return select_send::initialize_tables(join) ||
+           interceptor->initialize_tables(join);
+  }
+
+  virtual void cleanup()
+  {
+    select_send::cleanup();
+    interceptor->cleanup();
+  }
+};
+
+
+/******************************************************************************
+  External function implementations
+******************************************************************************/
+
+
+/**
+  Send a message as an "extra" column value
+
+  This function forms the 1st row of the QEP output with a simple text message.
+  This is useful to explain such trivial cases as "No tables used" etc.
+
+  @note Also this function explains the rest of QEP (subqueries or joined
+        tables if any).
+
+  @param thd      current THD
+  @param join     JOIN
+  @param message  text message for the "extra" column.
+
+  @return false if success, true if error
+*/
+
+bool explain_no_table(THD *thd, JOIN *join, const char *message)
+{
+  DBUG_ENTER("explain_no_table");
+  const bool ret= Explain_no_table(thd, join, message).send();
+  DBUG_RETURN(ret);
+}
+
+
+/**
+  Send a message as an "extra" column value
+
+  This function forms the 1st row of the QEP output with a simple text message.
+  This is useful to explain such trivial cases as "No tables used" etc.
+
+  @note Also this function explains the rest of QEP (subqueries if any).
+
+  @param thd      current THD
+  @param message  text message for the "extra" column.
+  @param rows     HA_POS_ERROR or a value for the "rows" column.
+
+  @return false if success, true if error
+*/
+
+bool explain_no_table(THD *thd, const char *message, ha_rows rows)
+{
+  DBUG_ENTER("explain_no_table");
+  const bool ret= Explain_no_table(thd, message, rows).send();
+  DBUG_RETURN(ret);
+
+}
+
+
+/**
+  EXPLAIN handling for single-table UPDATE and DELETE queries
+
+  Send to the client a QEP data set for single-table EXPLAIN UPDATE/DELETE
+  queries. As far as single-table UPDATE/DELETE are implemented without
+  the regular JOIN tree, we can't reuse mysql_explain_union() directly,
+  thus we deal with this single table in a special way and then call
+  mysql_explain_union() for subqueries (if any).
+
+  @param thd            current THD
+  @param table          TABLE object to update/delete rows in the UPDATE/DELETE
+                        query.
+  @param select         SQL_SELECT object that represents quick access methods/
+                        WHERE clause.
+  @param key            MAX_KEY or and index number of the key that was chosen
+                        to access table data.
+  @param limit          HA_POS_ERROR or LIMIT value.
+  @param need_tmp_table true if it requires temporary table -- "Using temporary"
+                        string in the "extra" column.
+  @param need_sort      true if it requires filesort() -- "Using filesort"
+                        string in the "extra" column.
+
+  @return false if success, true if error
+*/
+
+bool explain_single_table_modification(THD *thd,
+                                       TABLE *table,
+                                       const SQL_SELECT *select,
+                                       uint key,
+                                       ha_rows limit,
+                                       bool need_tmp_table,
+                                       bool need_sort)
+{
+  DBUG_ENTER("explain_single_table_modification");
+  const bool ret= Explain_table(thd, table, select, key, limit,
+                                need_tmp_table, need_sort).send();
+  DBUG_RETURN(ret);
+}
+
+
+/**
+  EXPLAIN handling for EXPLAIN SELECT queries
+
+  Send QEP to the client.
+
+  @param thd             current THD
+  @param join            JOIN
+  @param need_tmp_table  true if it requires a temporary table --
+                         "Using temporary" string in the "extra" column.
+  @param need_order      true if it requires filesort() -- "Using filesort"
+                         string in the "extra" column.
+  @param distinct        true if there is the DISTINCT clause (not optimized
+                         out) -- "Distinct" string in the "extra" column.
+
+  @return false if success, true if error
+*/
+
+bool explain_query_specification(THD *thd, JOIN *join, bool need_tmp_table,
+                                 bool need_order, bool distinct)
+{
+  DBUG_ENTER("explain_query_specification");
+  DBUG_PRINT("info", ("Select %p, type %s",
+		      join->select_lex, join->select_lex->type));
+  bool ret;
+  if (join->select_lex == join->unit->fake_select_lex)
+    ret= Explain_union(thd, join).send();
+  else
+    ret= Explain_join(thd, join, need_tmp_table, need_order, distinct).send();
+  DBUG_RETURN(ret);
+}
+
+
+/**
+  EXPLAIN handling for INSERT, REPLACE and multi-table UPDATE/DELETE queries
+
+  Send to the client a QEP data set for data-modifying commands those have a
+  regular JOIN tree (INSERT...SELECT, REPLACE...SELECT and multi-table
+  UPDATE and DELETE queries) like mysql_select() does for SELECT queries in
+  the "describe" mode.
+
+  @note @see explain_single_table_modification() for single-table
+        UPDATE/DELETE EXPLAIN handling.
+
+  @note Unlike the mysql_select function, explain_multi_table_modification
+        calls abort_result_set() itself in the case of failure (OOM etc.)
+        since explain_multi_table_modification() uses internally created
+        select_result stream.
+
+  @param thd     current THD
+  @param result  pointer to select_insert, multi_delete or multi_update object:
+                 the function uses it to call result->prepare(),
+                 result->prepare2() and result->initialize_tables() only but
+                 not to modify table data or to send a result to client.
+  @return false if success, true if error
+*/
+
+bool explain_multi_table_modification(THD *thd,
+                                      select_result_interceptor *result)
+{
+  DBUG_ENTER("explain_multi_table_modification");
+  explain_send explain(result);
+  bool res= explain_query_expression(thd, &explain);
+  DBUG_RETURN(res);
+}
+
+
+/**
+  EXPLAIN handling for SELECT and table-modifying queries that have JOIN
+
+  Send to the client a QEP data set for SELECT or data-modifying commands
+  those have a regular JOIN tree (INSERT...SELECT, REPLACE...SELECT and
+  multi-table UPDATE and DELETE queries) like mysql_select() does for SELECT
+  queries in the "describe" mode.
+
+  @note @see explain_single_table_modification() for single-table
+        UPDATE/DELETE EXPLAIN handling.
+
+  @note explain_query_expression() calls abort_result_set() itself in the
+        case of failure (OOM etc.) since explain_multi_table_modification()
+        uses internally created select_result stream.
+
+  @param thd     current THD
+  @param result  pointer to select_result, select_insert, multi_delete or
+                 multi_update object: the function uses it to call
+                 result->prepare(), result->prepare2() and
+                 result->initialize_tables() only but not to modify table data
+                 or to send a result to client.
+  @return false if success, true if error
+*/
+
+bool explain_query_expression(THD *thd, select_result *result)
+{
+  DBUG_ENTER("explain_query_expression");
+  const bool res= thd->send_explain_fields(result) ||
+                  mysql_explain_union(thd, &thd->lex->unit, result) ||
+                  thd->is_error();
+  /*
+    The code which prints the extended description is not robust
+    against malformed queries, so skip it if we have an error.
+  */
+  if (!res && (thd->lex->describe & DESCRIBE_EXTENDED) &&
+      thd->lex->sql_command == SQLCOM_SELECT) // TODO: implement for INSERT/etc
+  {
+    StringBuff<1024> str;
+    /*
+      The warnings system requires input in utf8, @see mysqld_show_warnings().
+    */
+    thd->lex->unit.print(&str, QT_TO_SYSTEM_CHARSET);
+    str.append('\0');
+    push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
+                 ER_YES, str.ptr());
+  }
+  if (res)
+    result->abort_result_set();
+  else
+    result->send_eof();
+  DBUG_RETURN(res);
+}
+
+
+/**
+  Explain UNION or subqueries of the unit
+
+  If the unit is a UNION, explain it as a UNION. Otherwise explain nested
+  subselects.
+
+  @param thd            thread object
+  @param unit           unit object
+  @param result         result stream to send QEP dataset
+
+  @return false if success, true if error
+*/
+bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
+{
+  DBUG_ENTER("mysql_explain_union");
+  bool res= 0;
+  SELECT_LEX *first= unit->first_select();
+
+  for (SELECT_LEX *sl= first;
+       sl;
+       sl= sl->next_select())
+  {
+    // drop UNCACHEABLE_EXPLAIN, because it is for internal usage only
+    uint8 uncacheable= (sl->uncacheable & ~UNCACHEABLE_EXPLAIN);
+    sl->type= (((&thd->lex->select_lex)==sl)?
+	       (sl->first_inner_unit() || sl->next_select() ?
+		"PRIMARY" : "SIMPLE"):
+	       ((sl == first)?
+		((sl->linkage == DERIVED_TABLE_TYPE) ?
+		 "DERIVED":
+		 ((uncacheable & UNCACHEABLE_DEPENDENT) ?
+		  "DEPENDENT SUBQUERY":
+		  (uncacheable?"UNCACHEABLE SUBQUERY":
+		   "SUBQUERY"))):
+		((uncacheable & UNCACHEABLE_DEPENDENT) ?
+		 "DEPENDENT UNION":
+		 uncacheable?"UNCACHEABLE UNION":
+		 "UNION")));
+    sl->options|= SELECT_DESCRIBE;
+  }
+  if (unit->is_union())
+  {
+    unit->fake_select_lex->select_number= UINT_MAX; // jost for initialization
+    unit->fake_select_lex->type= "UNION RESULT";
+    unit->fake_select_lex->options|= SELECT_DESCRIBE;
+    if (!(res= unit->prepare(thd, result, SELECT_NO_UNLOCK | SELECT_DESCRIBE)))
+      res= unit->exec();
+  }
+  else
+  {
+    thd->lex->current_select= first;
+    unit->set_limit(unit->global_parameters);
+    res= mysql_select(thd, &first->ref_pointer_array,
+			first->table_list.first,
+			first->with_wild, first->item_list,
+			first->where,
+			first->order_list.elements +
+			first->group_list.elements,
+			first->order_list.first,
+			first->group_list.first,
+			first->having,
+			thd->lex->proc_list.first,
+			first->options | thd->variables.option_bits | SELECT_DESCRIBE,
+			result, unit, first);
+  }
+  DBUG_RETURN(res || thd->is_error());
+}
+
+

=== added file 'sql/opt_explain.h'
--- sql/opt_explain.h	1970-01-01 00:00:00 +0000
+++ sql/opt_explain.h	2011-06-16 12:58:35 +0000
@@ -0,0 +1,73 @@
+/* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */
+
+
+#ifndef OPT_EXPLAIN_INCLUDED
+#define OPT_EXPLAIN_INCLUDED
+
+/** @file "EXPLAIN <command>"
+
+Single table UPDATE/DELETE commands are explained by the
+explain_single_table_modification() function.
+
+A query expression (complete SELECT query possibly including
+subqueries and unions), INSERT...SELECT and multitable UPDATE/DELETE
+commands are explained like this:
+
+(1) explain_query_expression()
+
+Is the entry point. Forwards the job to mysql_explain_union().
+
+(2) mysql_explain_union()
+
+Is for a SELECT_LEX_UNIT, prepares, optimizes, executes one JOIN for
+each "top-level" SELECT_LEXs of the unit (like: all SELECTs of a
+UNION; but not subqueries), and one JOIN for the fake SELECT_LEX of
+UNION); each JOIN execution (JOIN::exec()) calls explain_query_specification()
+
+(3) explain_query_specification()
+
+Is for a single SELECT_LEX (fake or not). It needs a prepared and
+optimized JOIN, for which it builds the EXPLAIN rows. But it also
+launches the EXPLAIN process for "inner units" (==subqueries of this
+SELECT_LEX), by calling mysql_explain_union() for each of them.
+*/
+
+class JOIN;
+class select_result;
+class select_result_interceptor;
+class SQL_SELECT;
+class TABLE;
+class THD;
+
+#include "my_base.h"
+
+bool explain_no_table(THD *thd, JOIN *join, const char *message);
+bool explain_no_table(THD *thd, const char *message,
+                      ha_rows rows= HA_POS_ERROR);
+bool explain_single_table_modification(THD *thd,
+                                       TABLE *table,
+                                       const SQL_SELECT *select,
+                                       uint key,
+                                       ha_rows limit,
+                                       bool need_tmp_table,
+                                       bool need_sort);
+bool explain_query_specification(THD *thd, JOIN *join, bool need_tmp_table,
+                                 bool need_order, bool distinct);
+bool explain_multi_table_modification(THD *thd,
+                                      select_result_interceptor *result);
+bool explain_query_expression(THD *thd, select_result *result);
+
+#endif /* OPT_EXPLAIN_INCLUDED */

=== modified file 'sql/opt_range.h'
--- sql/opt_range.h	2011-03-22 11:44:40 +0000
+++ sql/opt_range.h	2011-06-16 12:58:35 +0000
@@ -1,4 +1,4 @@
-/* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -427,8 +427,6 @@ protected:
    friend uint quick_range_seq_next(range_seq_t rseq, KEY_MULTI_RANGE *range);
    friend range_seq_t quick_range_seq_init(void *init_param,
                                            uint n_ranges, uint flags);
-  friend void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
-                              bool distinct,const char *message);
    friend class QUICK_SELECT_DESC;
    friend class QUICK_INDEX_MERGE_SELECT;
    friend class QUICK_ROR_INTERSECT_SELECT;

=== modified file 'sql/sql_class.h'
--- sql/sql_class.h	2011-03-24 08:00:03 +0000
+++ sql/sql_class.h	2011-06-16 12:58:35 +0000
@@ -3111,6 +3111,14 @@ public:
    */
    virtual void cleanup();
    void set_thd(THD *thd_arg) { thd= thd_arg; }
+
+  /**
+    If we execute EXPLAIN SELECT ... LIMIT (or any other EXPLAIN query)
+    we have to ignore offset value sending EXPLAIN output rows since
+    offset value belongs to the underlying query, not to the whole EXPLAIN.
+  */
+  void reset_offset_limit_cnt() { unit->offset_limit_cnt= 0; }
+
  #ifdef EMBEDDED_LIBRARY
    virtual void begin_dataset() {}
  #else
@@ -3808,6 +3816,11 @@ public:
  */
  #define CF_WRITE_RPL_INFO_COMMAND (1U << 12)

+/**
+  Identifies statements that can be explained with EXPLAIN.
+*/
+#define CF_CAN_BE_EXPLAINED       (1U << 13)
+
  /* Bits in server_command_flags */

  /**

=== modified file 'sql/sql_delete.cc'
--- sql/sql_delete.cc	2011-03-17 17:39:31 +0000
+++ sql/sql_delete.cc	2011-06-16 12:58:35 +0000
@@ -35,6 +35,7 @@
  #include "sp_head.h"
  #include "sql_trigger.h"
  #include "transaction.h"
+#include "opt_explain.h"
  #include "records.h"                            // init_read_record,
                                                  // end_read_record

@@ -60,6 +61,8 @@ bool mysql_delete(THD *thd, TABLE_LIST *
    ha_rows	deleted= 0;
    bool          reverse= FALSE;
    bool          skip_record;
+  bool          need_sort= FALSE;
+  bool          err= true;
    ORDER *order= (ORDER *) ((order_list && order_list->elements) ?
                             order_list->first : NULL);
    uint usable_index= MAX_KEY;
@@ -144,6 +147,13 @@ bool mysql_delete(THD *thd, TABLE_LIST *
      /* Update the table->file->stats.records number */
      table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
      ha_rows const maybe_deleted= table->file->stats.records;
+
+    if (thd->lex->describe)
+    {
+      err= explain_no_table(thd, "Deleting all rows", maybe_deleted);
+      goto exit_without_my_ok;
+    }
+
      DBUG_PRINT("debug", ("Trying to use delete_all_rows()"));
      if (!(error=table->file->ha_delete_all_rows()))
      {
@@ -169,14 +179,28 @@ bool mysql_delete(THD *thd, TABLE_LIST *
      Item::cond_result result;
      conds= remove_eq_conds(thd, conds, &result);
      if (result == Item::COND_FALSE)             // Impossible where
+    {
        limit= 0;
+
+      if (thd->lex->describe)
+      {
+        err= explain_no_table(thd, "Impossible WHERE");
+        goto exit_without_my_ok;
+      }
+    }
    }

  #ifdef WITH_PARTITION_STORAGE_ENGINE
    if (prune_partitions(thd, table, conds))
    {
+    /* No matching records */
+    if (thd->lex->describe)
+    {
+      err= explain_no_table(thd, "No matching records after partition pruning");
+      goto exit_without_my_ok;
+    }
+
      free_underlaid_joins(thd, select_lex);
-    // No matching record
      my_ok(thd, 0);
      DBUG_RETURN(0);
    }
@@ -219,23 +243,33 @@ bool mysql_delete(THD *thd, TABLE_LIST *
        DBUG_RETURN(TRUE);
      }
    }
+
+  if (order)
+  {
+    table->update_const_key_parts(conds);
+    order= simple_remove_const(order, conds);
+
+    usable_index= get_index_for_order(order, table, select, limit,
+                                      &need_sort, &reverse);
+  }
+
+  if (thd->lex->describe)
+  {
+    err= explain_single_table_modification(thd, table, select, usable_index,
+                                           limit, false, need_sort);
+    goto exit_without_my_ok;
+  }
+
    if (options & OPTION_QUICK)
      (void) table->file->extra(HA_EXTRA_QUICK);

-  if (order)
+  if (need_sort)
    {
      uint         length= 0;
      SORT_FIELD  *sortorder;
      ha_rows examined_rows;
      ha_rows found_rows;

-    table->update_const_key_parts(conds);
-    order= simple_remove_const(order, conds);
-
-    bool need_sort;
-    usable_index= get_index_for_order(order, table, select, limit,
-                                      &need_sort, &reverse);
-    if (need_sort)
      {
        DBUG_ASSERT(usable_index == MAX_KEY);
        table->sort.io_cache= (IO_CACHE *) my_malloc(sizeof(IO_CACHE),
@@ -361,6 +395,7 @@ bool mysql_delete(THD *thd, TABLE_LIST *
      (void) table->file->extra(HA_EXTRA_NORMAL);

  cleanup:
+  DBUG_ASSERT(!thd->lex->describe);
    /*
      Invalidate the table in the query cache if something changed. This must
      be before binlog writing and ha_autocommit_...
@@ -414,6 +449,11 @@ cleanup:
      DBUG_PRINT("info",("%ld records deleted",(long) deleted));
    }
    DBUG_RETURN(thd->is_error() || thd->killed);
+
+exit_without_my_ok:
+  delete select;
+  free_underlaid_joins(thd, select_lex);
+  DBUG_RETURN((err || thd->is_error() || thd->killed) ? 1 : 0);
  }



=== modified file 'sql/sql_insert.cc'
--- sql/sql_insert.cc	2011-02-15 17:14:15 +0000
+++ sql/sql_insert.cc	2011-06-16 12:58:35 +0000
@@ -76,6 +76,7 @@
  #include "transaction.h"
  #include "sql_audit.h"
  #include "debug_sync.h"
+#include "opt_explain.h"

  #ifndef EMBEDDED_LIBRARY
  static bool delayed_get_table(THD *thd, MDL_request *grl_protection_request,
@@ -453,11 +454,12 @@ void upgrade_lock_type(THD *thd, thr_loc
          the statement indirectly via a stored function or trigger:
          if it is used, that will lead to a deadlock between the
          client connection and the delayed thread.
+      - we're running the EXPLAIN INSERT command
      */
      if (specialflag & (SPECIAL_NO_NEW_FUNC | SPECIAL_SAFE_MODE) ||
          thd->variables.max_insert_delayed_threads == 0 ||
          thd->locked_tables_mode > LTM_LOCK_TABLES ||
-        thd->lex->uses_stored_routines())
+        thd->lex->uses_stored_routines() || thd->lex->describe)
      {
        *lock_type= TL_WRITE;
        return;
@@ -498,6 +500,7 @@ void upgrade_lock_type(THD *thd, thr_loc
          thread may be old and use the before-the-change value.
        */
        *lock_type= TL_WRITE;
+      return;
      }
    }
  }
@@ -657,6 +660,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
  		  bool ignore)
  {
    int error, res;
+  bool err= true;
    bool transactional_table, joins_freed= FALSE;
    bool changed;
    bool was_insert_delayed= (table_list->lock_type ==  TL_WRITE_DELAYED);
@@ -729,7 +733,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
                             !ignore && (thd->variables.sql_mode &
                                         (MODE_STRICT_TRANS_TABLES |
                                          MODE_STRICT_ALL_TABLES))))
-    goto abort;
+    goto exit_without_my_ok;

    /* mysql_prepare_insert set table_list->table if it was not set */
    table= table_list->table;
@@ -760,16 +764,27 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
      if (values->elements != value_count)
      {
        my_error(ER_WRONG_VALUE_COUNT_ON_ROW, MYF(0), counter);
-      goto abort;
+      goto exit_without_my_ok;
      }
      if (setup_fields(thd, 0, *values, MARK_COLUMNS_READ, 0, 0))
-      goto abort;
+      goto exit_without_my_ok;
    }
    its.rewind ();

    /* Restore the current context. */
    ctx_state.restore_state(context, table_list);

+  if (thd->lex->describe)
+  {
+    /*
+      Send "No tables used" and stop execution here since
+      there is no SELECT to explain.
+    */
+
+    err= explain_no_table(thd, "No tables used");
+    goto exit_without_my_ok;
+  }
+
    /*
      Fill in the given fields and dump it to the table file
    */
@@ -797,7 +812,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
        (info.handle_duplicates == DUP_UPDATE) &&
        (table->next_number_field != NULL) &&
        rpl_master_has_bug(active_mi->rli, 24432, TRUE, NULL, NULL))
-    goto abort;
+    goto exit_without_my_ok;
  #endif

    error=0;
@@ -1071,7 +1086,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
      table->file->extra(HA_EXTRA_WRITE_CANNOT_REPLACE);

    if (error)
-    goto abort;
+    goto exit_without_my_ok;
    if (values_list.elements == 1 && (!(thd->variables.option_bits & 
OPTION_WARNINGS) ||
  				    !thd->cuted_fields))
    {
@@ -1099,7 +1114,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *t
    thd->abort_on_warning= 0;
    DBUG_RETURN(FALSE);

-abort:
+exit_without_my_ok:
  #ifndef EMBEDDED_LIBRARY
    if (lock_type == TL_WRITE_DELAYED)
      end_delayed_insert(thd);
@@ -1109,7 +1124,7 @@ abort:
    if (!joins_freed)
      free_underlaid_joins(thd, &thd->lex->select_lex);
    thd->abort_on_warning= 0;
-  DBUG_RETURN(TRUE);
+  DBUG_RETURN(err);
  }



=== modified file 'sql/sql_parse.cc'
--- sql/sql_parse.cc	2011-03-17 17:39:31 +0000
+++ sql/sql_parse.cc	2011-06-16 12:58:35 +0000
@@ -64,7 +64,6 @@
                                // sp_grant_privileges, ...
  #include "sql_test.h"         // mysql_print_status
  #include "sql_select.h"       // handle_select, mysql_select,
-                              // mysql_explain_union
  #include "sql_load.h"         // mysql_load
  #include "sql_servers.h"      // create_servers, alter_servers,
                                // drop_servers, servers_reload
@@ -96,6 +95,7 @@
  #include "set_var.h"
  #include "mysql/psi/mysql_statement.h"
  #include "sql_bootstrap.h"
+#include "opt_explain.h"

  #define FLAGSTR(V,F) ((V)&(F)?#F" ":"")

@@ -322,22 +322,31 @@ void init_update_queries(void)
    sql_command_flags[SQLCOM_DROP_EVENT]=     CF_CHANGES_DATA | 
CF_AUTO_COMMIT_TRANS;

    sql_command_flags[SQLCOM_UPDATE]=	    CF_CHANGES_DATA | CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_UPDATE_MULTI]=   CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_INSERT]=	    CF_CHANGES_DATA | CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_INSERT_SELECT]=  CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_DELETE]=         CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_DELETE_MULTI]=   CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_REPLACE]=        CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_REPLACE_SELECT]= CF_CHANGES_DATA | 
CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_SELECT]=         CF_REEXECUTION_FRAGILE |
+                                            CF_CAN_BE_EXPLAINED |
                                              CF_CAN_GENERATE_ROW_EVENTS;
    sql_command_flags[SQLCOM_SET_OPTION]=     CF_REEXECUTION_FRAGILE | 
CF_AUTO_COMMIT_TRANS;
    sql_command_flags[SQLCOM_DO]=             CF_REEXECUTION_FRAGILE |
@@ -460,6 +469,13 @@ bool is_update_query(enum enum_sql_comma
    return (sql_command_flags[command] & CF_CHANGES_DATA) != 0;
  }

+
+bool is_explainable_query(enum enum_sql_command command)
+{
+  DBUG_ASSERT(command >= 0 && command <= SQLCOM_END);
+  return (sql_command_flags[command] & CF_CAN_BE_EXPLAINED) != 0;
+}
+
  /**
    Check if a sql command is allowed to write to log tables.
    @param command The SQL command
@@ -825,7 +841,7 @@ out:

    This is a helper function to mysql_execute_command.

-  @note SQLCOM_MULTI_UPDATE is an exception and delt with elsewhere.
+  @note SQLCOM_UPDATE_MULTI is an exception and delt with elsewhere.

    @see mysql_execute_command
    @returns Status code
@@ -1867,6 +1883,7 @@ mysql_execute_command(THD *thd)
    bool have_table_map_for_update= FALSE;
  #endif
    DBUG_ENTER("mysql_execute_command");
+  DBUG_ASSERT(!lex->describe || is_explainable_query(lex->sql_command));

  #ifdef WITH_PARTITION_STORAGE_ENGINE
    thd->work_part_info= 0;
@@ -2910,7 +2927,7 @@ end_with_restore_list:
    case SQLCOM_REPLACE_SELECT:
    case SQLCOM_INSERT_SELECT:
    {
-    select_result *sel_result;
+    select_insert *sel_result;
      DBUG_ASSERT(first_table == all_tables && first_table != 0);
      if ((res= insert_precheck(thd, all_tables)))
        break;
@@ -2941,21 +2958,26 @@ end_with_restore_list:
                                                   lex->duplicates,
                                                   lex->ignore)))
        {
-	res= handle_select(thd, lex, sel_result, OPTION_SETUP_TABLES_DONE);
-        /*
-          Invalidate the table in the query cache if something changed
-          after unlocking when changes become visible.
-          TODO: this is workaround. right way will be move invalidating in
-          the unlock procedure.
-        */
-        if (!res && first_table->lock_type ==  TL_WRITE_CONCURRENT_INSERT
&&
-            thd->lock)
+        if (lex->describe)
+          res= explain_multi_table_modification(thd, sel_result);
+        else
          {
-          /* INSERT ... SELECT should invalidate only the very first table */
-          TABLE_LIST *save_table= first_table->next_local;
-          first_table->next_local= 0;
-          query_cache_invalidate3(thd, first_table, 1);
-          first_table->next_local= save_table;
+          res= handle_select(thd, lex, sel_result, OPTION_SETUP_TABLES_DONE);
+          /*
+            Invalidate the table in the query cache if something changed
+            after unlocking when changes become visible.
+            TODO: this is workaround. right way will be move invalidating in
+            the unlock procedure.

RL: Please convert TODO to @todo

+          */
+          if (!res && first_table->lock_type ==  TL_WRITE_CONCURRENT_INSERT
&&
+              thd->lock)
+          {
+            /* INSERT ... SELECT should invalidate only the very first table */
+            TABLE_LIST *save_table= first_table->next_local;
+            first_table->next_local= 0;
+            query_cache_invalidate3(thd, first_table, 1);
+            first_table->next_local= save_table;
+          }
          }
          delete sel_result;
        }
@@ -3019,21 +3041,26 @@ end_with_restore_list:
      if (!thd->is_fatal_error &&
          (del_result= new multi_delete(aux_tables, lex->table_count)))
      {
-      res= mysql_select(thd, &select_lex->ref_pointer_array,
-			select_lex->get_table_list(),
-			select_lex->with_wild,
-			select_lex->item_list,
-			select_lex->where,
-			0, (ORDER *)NULL, (ORDER *)NULL, (Item *)NULL,
-			(ORDER *)NULL,
-			(select_lex->options | thd->variables.option_bits |
-			SELECT_NO_JOIN_CACHE | SELECT_NO_UNLOCK |
-                        OPTION_SETUP_TABLES_DONE) & ~OPTION_BUFFER_RESULT,
-			del_result, unit, select_lex);
-      res|= thd->is_error();
+      if (lex->describe)
+        res= explain_multi_table_modification(thd, del_result);
+      else
+      {
+        res= mysql_select(thd, &select_lex->ref_pointer_array,
+                          select_lex->get_table_list(),
+                          select_lex->with_wild,
+                          select_lex->item_list,
+                          select_lex->where,
+                          0, (ORDER *)NULL, (ORDER *)NULL, (Item *)NULL,
+                          (ORDER *)NULL,
+                          (select_lex->options | thd->variables.option_bits |
+                          SELECT_NO_JOIN_CACHE | SELECT_NO_UNLOCK |
+                          OPTION_SETUP_TABLES_DONE) & ~OPTION_BUFFER_RESULT,
+                          del_result, unit, select_lex);
+        res|= thd->is_error();
+        if (res)
+          del_result->abort_result_set();
+      }
        MYSQL_MULTI_DELETE_DONE(res, del_result->num_deleted());
-      if (res)
-        del_result->abort_result_set();
        delete del_result;
      }
      else
@@ -4501,7 +4528,7 @@ finish:
  static bool execute_sqlcom_select(THD *thd, TABLE_LIST *all_tables)
  {
    LEX	*lex= thd->lex;
-  select_result *result=lex->result;
+  select_result *result= lex->result;
    bool res;
    /* assign global limit variable if limit is not given */
    {
@@ -4523,30 +4550,7 @@ static bool execute_sqlcom_select(THD *t
        */
        if (!(result= new select_send()))
          return 1;                               /* purecov: inspected */
-      thd->send_explain_fields(result);
-      res= mysql_explain_union(thd, &thd->lex->unit, result);
-      /*
-        The code which prints the extended description is not robust
-        against malformed queries, so skip it if we have an error.
-      */
-      if (!res && (lex->describe & DESCRIBE_EXTENDED))
-      {
-        char buff[1024];
-        String str(buff,(uint32) sizeof(buff), system_charset_info);
-        str.length(0);
-        /*
-          The warnings system requires input in utf8, @see
-          mysqld_show_warnings().
-        */
-        thd->lex->unit.print(&str, QT_TO_SYSTEM_CHARSET);
-        str.append('\0');
-        push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
-                     ER_YES, str.ptr());
-      }
-      if (res)
-        result->abort_result_set();
-      else
-        result->send_eof();
+      res= explain_query_expression(thd, result);
        delete result;
      }
      else

=== modified file 'sql/sql_parse.h'
--- sql/sql_parse.h	2011-03-09 20:54:55 +0000
+++ sql/sql_parse.h	2011-06-16 12:58:35 +0000
@@ -80,6 +80,7 @@ bool check_identifier_name(LEX_STRING *s
                             uint err_code, const char *param_for_err_msg);
  bool mysql_test_parse_for_slave(THD *thd,char *inBuf,uint length);
  bool is_update_query(enum enum_sql_command command);
+bool is_explainable_query(enum enum_sql_command command);
  bool is_log_table_write_query(enum enum_sql_command command);
  bool is_rpl_info_table_write_query(enum enum_sql_command command);
  bool alloc_query(THD *thd, const char *packet, uint packet_length);

=== modified file 'sql/sql_select.cc'
--- sql/sql_select.cc	2011-03-29 07:30:44 +0000
+++ sql/sql_select.cc	2011-06-16 12:58:35 +0000
@@ -48,6 +48,7 @@
  #include <my_bit.h>
  #include <hash.h>
  #include <ft_global.h>
+#include "opt_explain.h"

  #define PREV_BITS(type,A)	((type) (((type) 1 << (A)) -1))

@@ -250,8 +251,6 @@ static bool setup_sum_funcs(THD *thd, It
  static bool prepare_sum_aggregators(Item_sum **func_ptr, bool need_distinct);
  static bool init_sum_functions(Item_sum **func, Item_sum **end);
  static bool update_sum_func(Item_sum **func);
-void select_describe(JOIN *join, bool need_tmp_table,bool need_order,
-			    bool distinct, const char *message=NullS);
  static Item *remove_additional_cond(Item* conds);
  static void add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab);
  static bool replace_subcondition(JOIN *join, Item **tree,
@@ -2794,8 +2793,8 @@ JOIN::exec()
    if (!tables_list && (tables || !select_lex->with_sum_func))
    {                                           // Only test of functions
      if (select_options & SELECT_DESCRIBE)
-      select_describe(this, FALSE, FALSE, FALSE,
-		      (zero_result_cause?zero_result_cause:"No tables used"));
+      explain_no_table(thd, this, zero_result_cause ? zero_result_cause
+                                                    : "No tables used");
      else
      {
        if (result->send_result_set_metadata(*columns_list,
@@ -2889,10 +2888,12 @@ JOIN::exec()
                                      keys_in_use_for_query))))
        order=0;
      having= tmp_having;
-    select_describe(this, need_tmp,
-		    order != 0 && !skip_sort_order,
-		    select_distinct,
-                    !tables ? "No tables used" : NullS);
+    if (tables)
+      explain_query_specification(thd, this, need_tmp,
+                                  order != 0 && !skip_sort_order,
+                                  select_distinct);
+    else
+      explain_no_table(thd, this, "No tables used");
      DBUG_VOID_RETURN;
    }

@@ -11938,7 +11939,7 @@ return_zero_rows(JOIN *join, select_resu

    if (select_options & SELECT_DESCRIBE)
    {
-    select_describe(join, FALSE, FALSE, FALSE, info);
+    explain_no_table(join->thd, join, info);
      DBUG_RETURN(0);
    }

@@ -22763,647 +22764,6 @@ void JOIN::clear()
    }
  }

-/**
-  EXPLAIN handling.
-
-  Send a description about what how the select will be done to stdout.
-*/
-
-void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
-                     bool distinct,const char *message)
-{
-  List<Item> field_list;
-  List<Item> item_list;
-  THD *thd=join->thd;
-  select_result *result=join->result;
-  Item *item_null= new Item_null();
-  CHARSET_INFO *cs= system_charset_info;
-  int quick_type;
-  DBUG_ENTER("select_describe");
-  DBUG_PRINT("info", ("Select 0x%lx, type %s, message %s",
-		      (ulong)join->select_lex, join->select_lex->type,
-		      message ? message : "NULL"));
-  /* Don't log this into the slow query log */
-  thd->server_status&= ~(SERVER_QUERY_NO_INDEX_USED | 
SERVER_QUERY_NO_GOOD_INDEX_USED);
-  join->unit->offset_limit_cnt= 0;
-
-  /*
-    NOTE: the number/types of items pushed into item_list must be in sync with
-    EXPLAIN column types as they're "defined" in THD::send_explain_fields()
-  */
-  if (message)
-  {
-    item_list.push_back(new Item_int((int32)
-				     join->select_lex->select_number));
-    item_list.push_back(new Item_string(join->select_lex->type,
-					strlen(join->select_lex->type), cs));
-    for (uint i=0 ; i < 7; i++)
-      item_list.push_back(item_null);
-    if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
-      item_list.push_back(item_null);
-    if (join->thd->lex->describe & DESCRIBE_EXTENDED)
-      item_list.push_back(item_null);
-
-    item_list.push_back(new Item_string(message,strlen(message),cs));
-    if (result->send_data(item_list))
-      join->error= 1;
-  }
-  else if (join->select_lex == join->unit->fake_select_lex)
-  {
-    /*
-      here we assume that the query will return at least two rows, so we
-      show "filesort" in EXPLAIN. Of course, sometimes we'll be wrong
-      and no filesort will be actually done, but executing all selects in
-      the UNION to provide precise EXPLAIN information will hardly be
-      appreciated :)
-    */
-    char table_name_buffer[NAME_CHAR_LEN];
-    item_list.empty();
-    /* id */
-    item_list.push_back(new Item_null);
-    /* select_type */
-    item_list.push_back(new Item_string(join->select_lex->type,
-					strlen(join->select_lex->type),
-					cs));
-    /* table */
-    {
-      SELECT_LEX *last_select= join->unit->first_select()->last_select();
-      // # characters needed to print select_number of last select
-      int last_length= (int)log10((double)last_select->select_number)+1;
-
-      SELECT_LEX *sl= join->unit->first_select();
-      uint len= 6, lastop= 0;
-      memcpy(table_name_buffer, STRING_WITH_LEN("<union"));
-      /*
-        - len + lastop: current position in table_name_buffer
-        - 6 + last_length: the number of characters needed to print
-          '...,'<last_select->select_number>'>\0'
-      */
-      for (;
-           sl && len + lastop + 6 + last_length < NAME_CHAR_LEN;
-           sl= sl->next_select())
-      {
-        len+= lastop;
-        lastop= my_snprintf(table_name_buffer + len, NAME_CHAR_LEN - len,
-                            "%u,", sl->select_number);
-      }
-      if (sl || len + lastop >= NAME_CHAR_LEN)
-      {
-        memcpy(table_name_buffer + len, STRING_WITH_LEN("...,"));
-        len+= 4;
-        lastop= my_snprintf(table_name_buffer + len, NAME_CHAR_LEN - len,
-                            "%u,", last_select->select_number);
-      }
-      len+= lastop;
-      table_name_buffer[len - 1]= '>';  // change ',' to '>'
-      item_list.push_back(new Item_string(table_name_buffer, len, cs));
-    }
-    /* partitions */
-    if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
-      item_list.push_back(item_null);
-    /* type */
-    item_list.push_back(new Item_string(join_type_str[JT_ALL],
-					  strlen(join_type_str[JT_ALL]),
-					  cs));
-    /* possible_keys */
-    item_list.push_back(item_null);
-    /* key*/
-    item_list.push_back(item_null);
-    /* key_len */
-    item_list.push_back(item_null);
-    /* ref */
-    item_list.push_back(item_null);
-    /* in_rows */
-    if (join->thd->lex->describe & DESCRIBE_EXTENDED)
-      item_list.push_back(item_null);
-    /* rows */
-    item_list.push_back(item_null);
-    /* extra */
-    if (join->unit->global_parameters->order_list.first)
-      item_list.push_back(new Item_string("Using filesort",
-					  14, cs));
-    else
-      item_list.push_back(new Item_string("", 0, cs));
-
-    if (result->send_data(item_list))
-      join->error= 1;
-  }
-  else
-  {
-    table_map used_tables=0;
-    uint last_sjm_table= MAX_TABLES;
-    for (uint i=0 ; i < join->tables ; i++)
-    {
-      JOIN_TAB *tab=join->join_tab+i;
-      TABLE *table=tab->table;
-      TABLE_LIST *table_list= tab->table->pos_in_table_list;
-      char buff[512];
-      char buff1[512], buff2[512], buff3[512];
-      char keylen_str_buf[64];
-      String extra(buff, sizeof(buff),cs);
-      char table_name_buffer[NAME_LEN];
-      String tmp1(buff1,sizeof(buff1),cs);
-      String tmp2(buff2,sizeof(buff2),cs);
-      String tmp3(buff3,sizeof(buff3),cs);
-      extra.length(0);
-      tmp1.length(0);
-      tmp2.length(0);
-      tmp3.length(0);
-
-      quick_type= -1;
-      item_list.empty();
-      /* id */
-      item_list.push_back(new Item_uint((uint32)
-				       join->select_lex->select_number));
-      /* select_type */
-      item_list.push_back(new Item_string(join->select_lex->type,
-                                          strlen(join->select_lex->type),
-                                          cs));
-      if (tab->type == JT_ALL && tab->select &&
tab->select->quick)
-      {
-        quick_type= tab->select->quick->get_type();
-        if ((quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE) ||
-            (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT) ||
-            (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION))
-          tab->type = JT_INDEX_MERGE;
-        else
-	  tab->type = JT_RANGE;
-      }
-      /* table */
-      if (table->derived_select_number)
-      {
-	/* Derived table name generation */
-	int len= my_snprintf(table_name_buffer, sizeof(table_name_buffer)-1,
-			     "<derived%u>",
-			     table->derived_select_number);
-	item_list.push_back(new Item_string(table_name_buffer, len, cs));
-      }
-      else
-      {
-        TABLE_LIST *real_table= table->pos_in_table_list;
-	item_list.push_back(new Item_string(real_table->alias,
-					    strlen(real_table->alias),
-					    cs));
-      }
-      /* "partitions" column */
-      if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
-      {
-#ifdef WITH_PARTITION_STORAGE_ENGINE
-        partition_info *part_info;
-        if (!table->derived_select_number &&
-            (part_info= table->part_info))
-        {
-          Item_string *item_str= new Item_string(cs);
-          make_used_partitions_str(part_info, &item_str->str_value);
-          item_list.push_back(item_str);
-        }
-        else
-          item_list.push_back(item_null);
-#else
-        /* just produce empty column if partitioning is not compiled in */
-        item_list.push_back(item_null);
-#endif
-      }
-      /* "type" column */
-      item_list.push_back(new Item_string(join_type_str[tab->type],
-					  strlen(join_type_str[tab->type]),
-					  cs));
-      /* Build "possible_keys" value and add it to item_list */
-      if (!tab->keys.is_clear_all())
-      {
-        uint j;
-        for (j=0 ; j < table->s->keys ; j++)
-        {
-          if (tab->keys.is_set(j))
-          {
-            if (tmp1.length())
-              tmp1.append(',');
-            tmp1.append(table->key_info[j].name,
-			strlen(table->key_info[j].name),
-			system_charset_info);
-          }
-        }
-      }
-      if (tmp1.length())
-	item_list.push_back(new Item_string(tmp1.ptr(),tmp1.length(),cs));
-      else
-	item_list.push_back(item_null);
-
-      /* Build "key", "key_len", and "ref" values and add them to item_list */
-      if (tab->ref.key_parts)
-      {
-	KEY *key_info=table->key_info+ tab->ref.key;
-        register uint length;
-	item_list.push_back(new Item_string(key_info->name,
-					    strlen(key_info->name),
-					    system_charset_info));
-        length= longlong2str(tab->ref.key_length, keylen_str_buf, 10) -
-                keylen_str_buf;
-        item_list.push_back(new Item_string(keylen_str_buf, length,
-                                            system_charset_info));
-	for (store_key **ref=tab->ref.key_copy ; *ref ; ref++)
-	{
-	  if (tmp2.length())
-	    tmp2.append(',');
-	  tmp2.append((*ref)->name(), strlen((*ref)->name()),
-		      system_charset_info);
-	}
-	item_list.push_back(new Item_string(tmp2.ptr(),tmp2.length(),cs));
-      }
-      else if (tab->type == JT_NEXT)
-      {
-	KEY *key_info=table->key_info+ tab->index;
-        register uint length;
-	item_list.push_back(new Item_string(key_info->name,
-					    strlen(key_info->name),cs));
-        length= longlong2str(key_info->key_length, keylen_str_buf, 10) -
-                keylen_str_buf;
-        item_list.push_back(new Item_string(keylen_str_buf,
-                                            length,
-                                            system_charset_info));
-	item_list.push_back(item_null);
-      }
-      else if (tab->select && tab->select->quick)
-      {
-        tab->select->quick->add_keys_and_lengths(&tmp2, &tmp3);
-	item_list.push_back(new Item_string(tmp2.ptr(),tmp2.length(),cs));
-	item_list.push_back(new Item_string(tmp3.ptr(),tmp3.length(),cs));
-	item_list.push_back(item_null);
-      }
-      else
-      {
-        if (table_list->schema_table &&
-            table_list->schema_table->i_s_requested_object &
OPTIMIZE_I_S_TABLE)
-        {
-          const char *tmp_buff;
-          int f_idx;
-          if (table_list->has_db_lookup_value)
-          {
-            f_idx= table_list->schema_table->idx_field1;
-            tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
-            tmp2.append(tmp_buff, strlen(tmp_buff), cs);
-          }
-          if (table_list->has_table_lookup_value)
-          {
-            if (table_list->has_db_lookup_value)
-              tmp2.append(',');
-            f_idx= table_list->schema_table->idx_field2;
-            tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
-            tmp2.append(tmp_buff, strlen(tmp_buff), cs);
-          }
-          if (tmp2.length())
-            item_list.push_back(new Item_string(tmp2.ptr(),tmp2.length(),cs));
-          else
-            item_list.push_back(item_null);
-        }
-        else
-          item_list.push_back(item_null);
-	item_list.push_back(item_null);
-	item_list.push_back(item_null);
-      }
-
-      /* Add "rows" field to item_list. */
-      if (table_list->schema_table)
-      {
-        /* in_rows */
-        if (join->thd->lex->describe & DESCRIBE_EXTENDED)
-          item_list.push_back(item_null);
-        /* rows */
-        item_list.push_back(item_null);
-      }
-      else
-      {
-        double examined_rows;
-        if (tab->select && tab->select->quick)
-          examined_rows= rows2double(tab->select->quick->records);
-        else if (tab->type == JT_NEXT || tab->type == JT_ALL)
-        {
-          if (tab->limit)
-            examined_rows= rows2double(tab->limit);
-          else
-          {
-            tab->table->file->info(HA_STATUS_VARIABLE);
-            examined_rows= rows2double(tab->table->file->stats.records);
-          }
-        }
-        else
-          examined_rows= join->best_positions[i].records_read;
-
-        item_list.push_back(new Item_int((longlong) (ulonglong) examined_rows,
-                                         MY_INT64_NUM_DECIMAL_DIGITS));
-
-        /* Add "filtered" field to item_list. */
-        if (join->thd->lex->describe & DESCRIBE_EXTENDED)
-        {
-          float f= 0.0;
-          if (examined_rows)
-            f= (float) (100.0 * join->best_positions[i].records_read /
-                        examined_rows);
-          item_list.push_back(new Item_float(f, 2));
-        }
-      }
-
-      /* Build "Extra" field and add it to item_list. */
-      my_bool key_read=table->key_read;
-      if ((tab->type == JT_NEXT || tab->type == JT_CONST) &&
-          table->covering_keys.is_set(tab->index))
-	key_read=1;
-      if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT &&
-          !((QUICK_ROR_INTERSECT_SELECT*)tab->select->quick)->need_to_fetch_row)
-        key_read=1;
-
-      if (tab->info)
-	item_list.push_back(new Item_string(tab->info,strlen(tab->info),cs));
-      else if (tab->packed_info & TAB_INFO_HAVE_VALUE)
-      {
-        if (tab->packed_info & TAB_INFO_USING_INDEX)
-          extra.append(STRING_WITH_LEN("; Using index"));
-        if (tab->packed_info & TAB_INFO_USING_WHERE)
-          extra.append(STRING_WITH_LEN("; Using where"));
-        if (tab->packed_info & TAB_INFO_FULL_SCAN_ON_NULL)
-          extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
-        /* Skip initial "; "*/
-        const char *str= extra.ptr();
-        uint32 len= extra.length();
-        if (len)
-        {
-          str += 2;
-          len -= 2;
-        }
-	item_list.push_back(new Item_string(str, len, cs));
-      }
-      else
-      {
-        uint keyno= MAX_KEY;
-        if (tab->ref.key_parts)
-          keyno= tab->ref.key;
-        else if (tab->select && tab->select->quick)
-          keyno = tab->select->quick->index;
-
-        if ((keyno != MAX_KEY && keyno ==
table->file->pushed_idx_cond_keyno &&
-             table->file->pushed_idx_cond) || tab->cache_idx_cond)
-          extra.append(STRING_WITH_LEN("; Using index condition"));
-
-        if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION ||
-            quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT ||
-            quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
-        {
-          extra.append(STRING_WITH_LEN("; Using "));
-          tab->select->quick->add_info_string(&extra);
-        }
-        if (tab->select)
-	{
-	  if (tab->use_quick == QS_DYNAMIC_RANGE)
-	  {
-            /* 4 bits per 1 hex digit + terminating '\0' */
-            char buf[MAX_KEY / 4 + 1];
-            extra.append(STRING_WITH_LEN("; Range checked for each "
-                                         "record (index map: 0x"));
-            extra.append(tab->keys.print(buf));
-            extra.append(')');
-	  }
-	  else if (tab->select->cond)
-          {
-            const Item *pushed_cond= tab->table->file->pushed_cond;
-
-            if 
(thd->optimizer_switch_flag(OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN) &&
-                pushed_cond)
-            {
-              extra.append(STRING_WITH_LEN("; Using where with pushed "
-                                           "condition"));
-              if (thd->lex->describe & DESCRIBE_EXTENDED)
-              {
-                extra.append(STRING_WITH_LEN(": "));
-                ((Item *)pushed_cond)->print(&extra, QT_ORDINARY);
-              }
-            }
-            else
-              extra.append(STRING_WITH_LEN("; Using where"));
-          }
-	}
-        if (table_list->schema_table &&
-            table_list->schema_table->i_s_requested_object &
OPTIMIZE_I_S_TABLE)
-        {
-          if (!table_list->table_open_method)
-            extra.append(STRING_WITH_LEN("; Skip_open_table"));
-          else if (table_list->table_open_method == OPEN_FRM_ONLY)
-            extra.append(STRING_WITH_LEN("; Open_frm_only"));
-          else
-            extra.append(STRING_WITH_LEN("; Open_full_table"));
-          if (table_list->has_db_lookup_value &&
-              table_list->has_table_lookup_value)
-            extra.append(STRING_WITH_LEN("; Scanned 0 databases"));
-          else if (table_list->has_db_lookup_value ||
-                   table_list->has_table_lookup_value)
-            extra.append(STRING_WITH_LEN("; Scanned 1 database"));
-          else
-            extra.append(STRING_WITH_LEN("; Scanned all databases"));
-        }
-        if (key_read)
-        {
-          if (quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
-          {
-            QUICK_GROUP_MIN_MAX_SELECT *qgs=
-              (QUICK_GROUP_MIN_MAX_SELECT *) tab->select->quick;
-            extra.append(STRING_WITH_LEN("; Using index for group-by"));
-            qgs->append_loose_scan_type(&extra);
-          }
-          else
-            extra.append(STRING_WITH_LEN("; Using index"));
-        }
-        if (table->reginfo.not_exists_optimize)
-          extra.append(STRING_WITH_LEN("; Not exists"));
-
-        if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE &&
-            !(((QUICK_RANGE_SELECT*)(tab->select->quick))->mrr_flags &
-             (HA_MRR_USE_DEFAULT_IMPL | HA_MRR_SORTED)))
-        {
-          /*
-            During normal execution of a query, multi_range_read_init() is
-            called to initialize MRR. If HA_MRR_SORTED is set at this point,
-            multi_range_read_init() for any native MRR implementation will
-            revert to default MRR because they cannot produce sorted output
-            currently.
-            Calling multi_range_read_init() can potentially be costly, so it
-            is not done when executing an EXPLAIN. We therefore make the
-            assumption that HA_MRR_SORTED means no MRR. If some MRR native
-            implementation will support sorted output in the future, a
-            function "bool mrr_supports_sorted()" should be added in the
-            handler.
-          */
-          extra.append(STRING_WITH_LEN("; Using MRR"));
-        }
-        if (need_tmp_table)
-        {
-          need_tmp_table=0;
-          extra.append(STRING_WITH_LEN("; Using temporary"));
-        }
-        if (need_order)
-        {
-          need_order=0;
-          extra.append(STRING_WITH_LEN("; Using filesort"));
-        }
-        if (distinct & test_all_bits(used_tables,thd->used_tables))
-          extra.append(STRING_WITH_LEN("; Distinct"));
-
-        if (tab->loosescan_match_tab)
-        {
-          extra.append(STRING_WITH_LEN("; LooseScan"));
-        }
-
-        if (tab->flush_weedout_table)
-          extra.append(STRING_WITH_LEN("; Start temporary"));
-        if (tab->check_weed_out_table)
-          extra.append(STRING_WITH_LEN("; End temporary"));
-        else if (tab->do_firstmatch)
-        {
-          if (tab->do_firstmatch == join->join_tab - 1)
-            extra.append(STRING_WITH_LEN("; FirstMatch"));
-          else
-          {
-            extra.append(STRING_WITH_LEN("; FirstMatch("));
-            TABLE *prev_table=tab->do_firstmatch->table;
-            if (prev_table->derived_select_number)
-            {
-              char namebuf[NAME_LEN];
-              /* Derived table name generation */
-              int len= my_snprintf(namebuf, sizeof(namebuf)-1,
-                                   "<derived%u>",
-                                   prev_table->derived_select_number);
-              extra.append(namebuf, len);
-            }
-            else
-              extra.append(prev_table->pos_in_table_list->alias);
-            extra.append(STRING_WITH_LEN(")"));
-          }
-        }
-        uint sj_strategy= join->best_positions[i].sj_strategy;
-        if (sj_is_materialize_strategy(sj_strategy))
-        {
-          if (join->best_positions[i].n_sj_tables == 1)
-            extra.append(STRING_WITH_LEN("; Materialize"));
-          else
-          {
-            last_sjm_table= i + join->best_positions[i].n_sj_tables - 1;
-            extra.append(STRING_WITH_LEN("; Start materialize"));
-          }
-          if (sj_strategy == SJ_OPT_MATERIALIZE_SCAN)
-              extra.append(STRING_WITH_LEN("; Scan"));
-        }
-        else if (last_sjm_table == i)
-        {
-          extra.append(STRING_WITH_LEN("; End materialize"));
-        }
-
-        for (uint part= 0; part < tab->ref.key_parts; part++)
-        {
-          if (tab->ref.cond_guards[part])
-          {
-            extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
-            break;
-          }
-        }
-
-        if (i > 0 && tab[-1].next_select == sub_select_cache)
-        {
-          extra.append(STRING_WITH_LEN("; Using join buffer ("));
-          if ((tab->use_join_cache & JOIN_CACHE::ALG_BNL))
-            extra.append(STRING_WITH_LEN("BNL"));
-          else if ((tab->use_join_cache & JOIN_CACHE::ALG_BKA))
-            extra.append(STRING_WITH_LEN("BKA"));
-          else if ((tab->use_join_cache & JOIN_CACHE::ALG_BKA_UNIQUE))
-            extra.append(STRING_WITH_LEN("BKA_UNIQUE"));
-          else
-            DBUG_ASSERT(0);
-          if (tab->use_join_cache & JOIN_CACHE::NON_INCREMENTAL_BUFFER)
-            extra.append(STRING_WITH_LEN(", regular buffers)"));
-          else
-            extra.append(STRING_WITH_LEN(", incremental buffers)"));
-        }
-
-        /* Skip initial "; "*/
-        const char *str= extra.ptr();
-        uint32 len= extra.length();
-        if (len)
-        {
-          str += 2;
-          len -= 2;
-        }
-        item_list.push_back(new Item_string(str, len, cs));
-      }
-      // For next iteration
-      used_tables|=table->map;
-      if (result->send_data(item_list))
-	join->error= 1;
-    }
-  }
-  for (SELECT_LEX_UNIT *unit= join->select_lex->first_inner_unit();
-       unit;
-       unit= unit->next_unit())
-  {
-    if (mysql_explain_union(thd, unit, result))
-      DBUG_VOID_RETURN;
-  }
-  DBUG_VOID_RETURN;
-}
-
-
-bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
-{
-  DBUG_ENTER("mysql_explain_union");
-  bool res= 0;
-  SELECT_LEX *first= unit->first_select();
-
-  for (SELECT_LEX *sl= first;
-       sl;
-       sl= sl->next_select())
-  {
-    // drop UNCACHEABLE_EXPLAIN, because it is for internal usage only
-    uint8 uncacheable= (sl->uncacheable & ~UNCACHEABLE_EXPLAIN);
-    sl->type= (((&thd->lex->select_lex)==sl)?
-	       (sl->first_inner_unit() || sl->next_select() ?
-		"PRIMARY" : "SIMPLE"):
-	       ((sl == first)?
-		((sl->linkage == DERIVED_TABLE_TYPE) ?
-		 "DERIVED":
-		 ((uncacheable & UNCACHEABLE_DEPENDENT) ?
-		  "DEPENDENT SUBQUERY":
-		  (uncacheable?"UNCACHEABLE SUBQUERY":
-		   "SUBQUERY"))):
-		((uncacheable & UNCACHEABLE_DEPENDENT) ?
-		 "DEPENDENT UNION":
-		 uncacheable?"UNCACHEABLE UNION":
-		 "UNION")));
-    sl->options|= SELECT_DESCRIBE;
-  }
-  if (unit->is_union())
-  {
-    unit->fake_select_lex->select_number= UINT_MAX; // jost for initialization
-    unit->fake_select_lex->type= "UNION RESULT";
-    unit->fake_select_lex->options|= SELECT_DESCRIBE;
-    if (!(res= unit->prepare(thd, result, SELECT_NO_UNLOCK | SELECT_DESCRIBE)))
-      res= unit->exec();
-  }
-  else
-  {
-    thd->lex->current_select= first;
-    unit->set_limit(unit->global_parameters);
-    res= mysql_select(thd, &first->ref_pointer_array,
-			first->table_list.first,
-			first->with_wild, first->item_list,
-			first->where,
-			first->order_list.elements +
-			first->group_list.elements,
-			first->order_list.first,
-			first->group_list.first,
-			first->having,
-			thd->lex->proc_list.first,
-			first->options | thd->variables.option_bits | SELECT_DESCRIBE,
-			result, unit, first);
-  }
-  DBUG_RETURN(res || thd->is_error());
-}
-

  static void print_table_array(THD *thd, String *str, TABLE_LIST **table,
                                TABLE_LIST **end, enum_query_type query_type)

=== modified file 'sql/sql_select.h'
--- sql/sql_select.h	2011-03-29 07:30:44 +0000
+++ sql/sql_select.h	2011-06-16 12:58:35 +0000
@@ -2248,8 +2248,6 @@ bool mysql_select(THD *thd, Item ***rref
                    select_result *result, SELECT_LEX_UNIT *unit,
                    SELECT_LEX *select_lex);
  void free_underlaid_joins(THD *thd, SELECT_LEX *select);
-bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit,
-                         select_result *result);
  Field *create_tmp_field(THD *thd, TABLE *table,Item *item, Item::Type type,
  			Item ***copy_func, Field **from_field,
                          Field **def_field,

=== modified file 'sql/sql_show.cc'
--- sql/sql_show.cc	2011-03-28 08:10:39 +0000
+++ sql/sql_show.cc	2011-06-16 12:58:35 +0000
@@ -20,7 +20,7 @@
  #include "sql_priv.h"
  #include "unireg.h"
  #include "sql_acl.h"                        // fill_schema_*_privileges
-#include "sql_select.h"                         // For select_describe
+#include "sql_select.h"
  #include "sql_base.h"                       // close_tables_for_reopen
  #include "sql_show.h"
  #include "sql_table.h"                        // filename_to_tablename,

=== modified file 'sql/sql_string.h'
--- sql/sql_string.h	2011-03-22 11:44:40 +0000
+++ sql/sql_string.h	2011-06-16 12:58:35 +0000
@@ -422,6 +422,32 @@ public:
    }
  };

+
+/**
+  String class wrapper with a preallocated buffer of size buff_sz
+
+  This class allows to replace sequences of:
+     char buff[12345];
+     String str(buff, sizeof(buff));
+     str.length(0);
+  with a simple equivalent declaration:
+     StringBuff<12345> str;
+*/
+
+template<size_t buff_sz>
+class StringBuff : public String

RL: I'd appreciate it if you spell out the name: StringBuffer

+{
+  char buff[buff_sz];
+
+public:
+  StringBuff() : String(buff, buff_sz, &my_charset_bin) { length(0); }
+  explicit StringBuff(const CHARSET_INFO *cs) : String(buff, buff_sz, cs)
+  {
+    length(0);
+  }
+};
+
+
  static inline bool check_if_only_end_space(const CHARSET_INFO *cs, char *str,
                                             char *end)
  {

=== modified file 'sql/sql_update.cc'
--- sql/sql_update.cc	2011-02-25 16:41:57 +0000
+++ sql/sql_update.cc	2011-06-16 12:58:35 +0000
@@ -38,6 +38,7 @@
  #include "records.h"                            // init_read_record,
                                                  // end_read_record
  #include "filesort.h"                           // filesort
+#include "opt_explain.h"
  #include "sql_derived.h" // mysql_derived_prepare,
                           // mysql_handle_derived,
                           // mysql_derived_filling
@@ -262,10 +263,12 @@ int mysql_update(THD *thd,
    bool		safe_update= test(thd->variables.option_bits & OPTION_SAFE_UPDATES);
    bool          used_key_is_modified= FALSE, transactional_table, will_batch;
    int           res;
-  int		error, loc_error;
+  int           error= 1;
+  int           loc_error;
    uint          used_index, dup_key_found;
    bool          need_sort= TRUE;
    bool          reverse= FALSE;
+  bool          using_filesort;
  #ifndef NO_EMBEDDED_ACCESS_CHECKS
    uint		want_privilege;
  #endif
@@ -273,7 +276,7 @@ int mysql_update(THD *thd,
    ha_rows	updated, found;
    key_map	old_covering_keys;
    TABLE		*table;
-  SQL_SELECT	*select;
+  SQL_SELECT	*select= 0;

RL: = NULL, please

    READ_RECORD	info;
    SELECT_LEX    *select_lex= &thd->lex->select_lex;
    ulonglong     id;
@@ -305,7 +308,8 @@ int mysql_update(THD *thd,
      mysql_handle_derived(thd->lex, &mysql_derived_cleanup);
      DBUG_RETURN(1);
    }
-  mysql_handle_derived(thd->lex, &mysql_derived_cleanup);
+  if (!thd->lex->describe)
+    mysql_handle_derived(thd->lex, &mysql_derived_cleanup);

    THD_STAGE_INFO(thd, stage_init);
    table= table_list->table;
@@ -392,7 +396,14 @@ int mysql_update(THD *thd,

  #ifdef WITH_PARTITION_STORAGE_ENGINE
    if (prune_partitions(thd, table, conds))
-  {
+  { // No matching records
+    if (thd->lex->describe)
+    {
+      error= explain_no_table(thd,
+                              "No matching records after partition pruning");
+      goto exit_without_my_ok;
+    }

RL: Can I ask you to replace the text above with "No matching rows ..." ?

+
      free_underlaid_joins(thd, select_lex);
      my_ok(thd);				// No matching records
      DBUG_RETURN(0);
@@ -406,6 +417,12 @@ int mysql_update(THD *thd,
    if (error || !limit ||
        (select && select->check_quick(thd, safe_update, limit)))
    {
+    if (thd->lex->describe && !error && !thd->is_error())
+    {
+      error= explain_no_table(thd, "Impossible WHERE");
+      goto exit_without_my_ok;
+    }

RL: The logic here is quite unmaintaintable - it should be refactored.
RL: However, not a mandatory review comment.
+
      delete select;
      free_underlaid_joins(thd, select_lex);
      /*
@@ -431,7 +448,7 @@ int mysql_update(THD *thd,
      {
        my_message(ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE,
  		 ER(ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE), MYF(0));
-      goto err;
+      goto exit_without_my_ok;
      }
    }
    init_ftfuncs(thd, select_lex, 1);
@@ -451,11 +468,21 @@ int mysql_update(THD *thd,
    }

  #ifdef WITH_PARTITION_STORAGE_ENGINE
-  if (used_key_is_modified || order ||
-      partition_key_modified(table, table->write_set))
-#else
-  if (used_key_is_modified || order)
+  used_key_is_modified|= partition_key_modified(table, table->write_set);
  #endif
+
+  using_filesort= order && (need_sort||used_key_is_modified);
+  if (thd->lex->describe)
+  {
+    const bool using_tmp_table= !using_filesort &&
+                                (used_key_is_modified || order);
+    error= explain_single_table_modification(thd, table, select, used_index,
+                                             limit, using_tmp_table,
+                                             using_filesort);
+    goto exit_without_my_ok;
+  }
+
+  if (used_key_is_modified || order)
    {
      /*
        We can't update table directly;  We must first search after all
@@ -469,7 +496,7 @@ int mysql_update(THD *thd,
      }

      /* note: We avoid sorting if we sort on the used index */
-    if (order && (need_sort || used_key_is_modified))
+    if (using_filesort)
      {
        /*
  	Doing an ORDER BY;  Let filesort find and sort the rows we are going
@@ -490,7 +517,7 @@ int mysql_update(THD *thd,
                                                 &examined_rows, &found_rows))
            == HA_POS_ERROR)
        {
-	goto err;
+	goto exit_without_my_ok;

RL: Some of the "goto exit_without_my_ok" lines contain TAB characters.

        }
        thd->inc_examined_row_count(examined_rows);
        /*
@@ -511,11 +538,11 @@ int mysql_update(THD *thd,
        IO_CACHE tempfile;
        if (open_cached_file(&tempfile, mysql_tmpdir,TEMP_PREFIX,
  			   DISK_BUFFER_SIZE, MYF(MY_WME)))
-	goto err;
+	goto exit_without_my_ok;

        /* If quick select is used, initialize it before retrieving rows. */
        if (select && select->quick && select->quick->reset())
-        goto err;
+        goto exit_without_my_ok;
        table->file->try_semi_consistent_read(1);

        /*
@@ -592,7 +619,7 @@ int mysql_update(THD *thd,
  	error=1; /* purecov: inspected */
        select->file=tempfile;			// Read row ptrs from this file
        if (error >= 0)
-	goto err;
+	goto exit_without_my_ok;
      }
      if (table->key_read)
        table->restore_column_maps_after_mark_index();
@@ -602,7 +629,7 @@ int mysql_update(THD *thd,
      table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);

    if (select && select->quick && select->quick->reset())
-    goto err;
+    goto exit_without_my_ok;
    table->file->try_semi_consistent_read(1);
    init_read_record(&info, thd, table, select, 0, 1, FALSE);

@@ -911,12 +938,12 @@ int mysql_update(THD *thd,
    *updated_return= updated;
    DBUG_RETURN((error >= 0 || thd->is_error()) ? 1 : 0);

-err:
+exit_without_my_ok:
    delete select;
    free_underlaid_joins(thd, select_lex);
    table->set_keyread(FALSE);
    thd->abort_on_warning= 0;
-  DBUG_RETURN(1);
+  DBUG_RETURN(error);
  }

  /*
@@ -1301,7 +1328,8 @@ int mysql_multi_update_prepare(THD *thd)
      mysql_handle_derived(lex, &mysql_derived_cleanup);
      DBUG_RETURN(TRUE);
    }
-  mysql_handle_derived(lex, &mysql_derived_cleanup);
+  if (!thd->lex->describe)
+    mysql_handle_derived(lex, &mysql_derived_cleanup);

    DBUG_RETURN (FALSE);
  }
@@ -1338,24 +1366,29 @@ bool mysql_multi_update(THD *thd,
                                (MODE_STRICT_TRANS_TABLES |
                                 MODE_STRICT_ALL_TABLES));

-  List<Item> total_list;
+  if (thd->lex->describe)
+    res= explain_multi_table_modification(thd, *result);
+  else
+  {
+    List<Item> total_list;

-  res= mysql_select(thd, &select_lex->ref_pointer_array,
-                    table_list, select_lex->with_wild,
-                    total_list,
-                    conds, 0, (ORDER *) NULL, (ORDER *)NULL, (Item *) NULL,
-                    (ORDER *)NULL,
-                    options | SELECT_NO_JOIN_CACHE | SELECT_NO_UNLOCK |
-                    OPTION_SETUP_TABLES_DONE,
-                    *result, unit, select_lex);
-
-  DBUG_PRINT("info",("res: %d  report_error: %d", res, (int) thd->is_error()));
-  res|= thd->is_error();
-  if (unlikely(res))
-  {
-    /* If we had a another error reported earlier then this will be ignored */
-    (*result)->send_error(ER_UNKNOWN_ERROR, ER(ER_UNKNOWN_ERROR));
-    (*result)->abort_result_set();
+    res= mysql_select(thd, &select_lex->ref_pointer_array,
+                      table_list, select_lex->with_wild,
+                      total_list,
+                      conds, 0, (ORDER *) NULL, (ORDER *)NULL, (Item *) NULL,
+                      (ORDER *)NULL,
+                      options | SELECT_NO_JOIN_CACHE | SELECT_NO_UNLOCK |
+                      OPTION_SETUP_TABLES_DONE,
+                      *result, unit, select_lex);
+
+    DBUG_PRINT("info",("res: %d  report_error: %d",res, (int) thd->is_error()));
+    res|= thd->is_error();
+    if (unlikely(res))
+    {
+      /* If we had a another error reported earlier then this will be ignored */
+      (*result)->send_error(ER_UNKNOWN_ERROR, ER(ER_UNKNOWN_ERROR));
+      (*result)->abort_result_set();
+    }
    }
    thd->abort_on_warning= 0;
    DBUG_RETURN(res);

=== modified file 'sql/sql_view.cc'
--- sql/sql_view.cc	2011-03-17 17:39:31 +0000
+++ sql/sql_view.cc	2011-06-16 12:58:35 +0000
@@ -1277,8 +1277,8 @@ bool mysql_make_view(THD *thd, File_pars
        underlying tables.
        Skip this step if we are opening view for prelocking only.
      */
-    if (!table->prelocking_placeholder &&
-        (old_lex->sql_command == SQLCOM_SELECT && old_lex->describe))
+    if (!table->prelocking_placeholder && old_lex->describe &&
+        is_explainable_query(old_lex->sql_command))
      {
        if (check_table_access(thd, SELECT_ACL, view_tables, FALSE,
                               UINT_MAX, TRUE) &&

=== modified file 'sql/sql_yacc.yy'
--- sql/sql_yacc.yy	2011-03-09 20:54:55 +0000
+++ sql/sql_yacc.yy	2011-06-16 12:58:35 +0000
@@ -11371,11 +11371,16 @@ describe:
            opt_describe_column {}
          | describe_command opt_extended_describe
            { Lex->describe|= DESCRIBE_NORMAL; }
+          explanable_command
+          { Lex->select_lex.options|= SELECT_DESCRIBE; }
+        ;
+
+explanable_command:
            select
-          {
-            LEX *lex=Lex;
-            lex->select_lex.options|= SELECT_DESCRIBE;
-          }
+        | insert
+        | replace
+        | update
+        | delete
          ;

  describe_command:


Thanks,
Roy
Thread
WL4897: Review commentsRoy Lyseng19 Jun
  • Re: WL4897: Review commentsGleb Shchepa19 Jun
    • Re: WL4897: Review commentsRoy Lyseng20 Jun