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ChangeSet@stripped, 2007-04-20 11:56:28+03:00, mhansson@stripped +3 -0
Bug#27573: MIN() on an indexed column which is always NULL sets _other_ results
to NULL
We have the following case:
SELECT MIN(keypart2),... FROM t1 WHERE keypart1 = constant;
There is an optimization which will substitute a constant for
MIN(keypart2), inserting the 1) minimum non-null value where the
WHERE clause still matches, or 2) null if there are only NULL
values for keypart2. If no row matches, the result will be 3) a row
of NULLs.
The previous implementation skipped step 2, and went straight to
a row of NULLs.
mysql-test/r/func_group.result@stripped, 2007-04-20 11:56:26+03:00, mhansson@stripped +44 -0
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
Correct result
mysql-test/t/func_group.test@stripped, 2007-04-20 11:56:26+03:00, mhansson@stripped +33 -0
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
test case
sql/opt_sum.cc@stripped, 2007-04-20 11:56:26+03:00, mhansson@stripped +95 -10
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
Added function read_next_or_current that will try to read the
first non-null value for a given complete-field prefix, second
choice is to read the null, and lastly return an error if no row
is found.
# This is a BitKeeper patch. What follows are the unified diffs for the
# set of deltas contained in the patch. The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User: mhansson
# Host: linux-st28.site
# Root: /home/martin/mysql/src/5.0o-bug27573
--- 1.61/sql/opt_sum.cc 2007-01-30 23:09:25 +02:00
+++ 1.62/sql/opt_sum.cc 2007-04-20 11:56:26 +03:00
@@ -51,7 +51,9 @@ static bool find_key_for_maxmin(bool max
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint range_fl, uint prefix_len);
static int maxmin_in_range(bool max_fl, Field* field, COND *cond);
-
+static int read_next_or_current(TABLE *table, TABLE_REF *ref,
+ bool is_nullable, uint prefix_len,
+ Field *field);
/*
Substitutes constants for some COUNT(), MIN() and MAX() functions.
@@ -206,12 +208,11 @@ int opt_sum_query(TABLE_LIST *tables, Li
if (!ref.key_length)
error= table->file->index_first(table->record[0]);
- else
- error= table->file->index_read(table->record[0],key_buff,
- ref.key_length,
- range_fl & NEAR_MIN ?
- HA_READ_AFTER_KEY :
- HA_READ_KEY_OR_NEXT);
+ else
+ error= read_next_or_current(table, &ref,
+ range_fl & NEAR_MIN, prefix_len,
+ item_field->field );
+
if (!error && reckey_in_range(0, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
@@ -739,13 +740,23 @@ static bool find_key_for_maxmin(bool max
if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
{
/*
- SELECT MIN(key_part2) FROM t1 WHERE key_part1=const
- If key_part2 may be NULL, then we want to find the first row
- that is not null
+ SELECT MIN(key_part2) FROM t1 WHERE key_part1=const
+
+ If key_part2 may be NULL, then we want to find the first
+ row that is not null. So we set the first byte that
+ comes after key_part1 to 1. This means that the key
+ buffer now contains {const, NULL}. This key buffer will
+ be passed to the handler along with a flag, NEAR_MIN,
+ that tells it to retrieve the record that is stored
+ after this key buffer. This is handled by function
+ read_next_or_current(). This function is smart enough to
+ backtrack and see if the original key {const, NULL} is
+ present if there is no key after it.
*/
ref->key_buff[ref->key_length]= 1;
ref->key_length+= part->store_length;
*range_fl&= ~NO_MIN_RANGE;
+ /* Exclusive interval, we prefer the value after this key */
*range_fl|= NEAR_MIN; // > NULL
}
/*
@@ -858,3 +869,77 @@ static int maxmin_in_range(bool max_fl,
return 0;
}
+/*
+ Try to read the next key from the the table's index, or the given
+ key if none exists.
+
+ @param table In. The table that the key belongs to.
+ @param key_buffer In/Out. Complete-field prefix of a key in handler format.
+ @param key_length In. Length of the buffer
+ @param exclusive In. Used to indicate that either the last
+ keypart is column containing NULLs, see below,
+ or that we want the smallest value in an
+ exclusive interval, i.e. using <.
+ @details
+ This function is used to read the minimum value for a
+ complete-field prefix key. If exclusive is true, The next
+ different tuple will be read, if it exists. If it doesn't, the
+ function will backtrack to see if the n:th keypart is NULL for
+ this column. In that case the record read by backtracking will be
+ returned. Otherwise the index position is restored and
+ HA_ERR_KEY_NOT_FOUND is returned.
+
+ @return
+ 0: A record was successfully read from the index.
+ other: An error from the handler, see handler::index_read.
+ */
+static int read_next_or_current(TABLE *table, TABLE_REF *ref, bool exclusive,
+ uint prefix_len, Field *field)
+{
+ int error;
+ int key_length= ref->key_length;
+ byte *key_buffer= ref->key_buff;
+ handler *file= table->file;
+ byte* data_buffer= table->record[0];
+
+ if (!exclusive)
+ /* The interval is inclusive, we want the current record. This
+ usually means it has been determined that there are no NULLs in
+ the column we are searching. It could also mean that we have a
+ >= predicate for the wanted value.
+ */
+ return file->index_read(data_buffer, key_buffer, key_length,
+ HA_READ_KEY_OR_NEXT);
+
+ /*
+ The interval is not inclusive. Hence, we are either doing a MIN(c)
+ where c is the minimum column and NULLs are known to be in this
+ column, or we have a predicate c > something. Either way, we want
+ to scan the next record.
+ */
+ error= file->index_read(data_buffer, key_buffer, key_length,
+ HA_READ_AFTER_KEY);
+
+ if (error == HA_ERR_KEY_NOT_FOUND ||
+ key_cmp_if_same(table, ref->key_buff, ref->key, prefix_len)) {
+ /*
+ We are either at the end of the index, or we just read a value
+ where the prefix is different. Depending on what we're doing, we
+ should take a step backward, or just keep what we have and exit
+ (even if we have nothing) However, in order to know, we must
+ take that step backards.
+ */
+ error= file->index_read(data_buffer, key_buffer, key_length,
+ HA_READ_KEY_OR_PREV);
+ if (!field->is_null())
+ /*
+ So, after taking a step backwards, we find that the sought
+ value for the column is not NULL. This means that we were
+ *not* looking for a MIN() value (because then it would have
+ been NULL. Hence, advance the index position again.
+ */
+ return file->index_read(data_buffer, key_buffer, key_length,
+ HA_READ_AFTER_KEY);
+ }
+ return error;
+}
--- 1.59/mysql-test/r/func_group.result 2007-02-27 09:01:57 +02:00
+++ 1.60/mysql-test/r/func_group.result 2007-04-20 11:56:26 +03:00
@@ -1321,4 +1321,48 @@ SELECT a,AVG(DISTINCT b) AS average FROM
a average
1 32768.5000
DROP TABLE t1;
+CREATE TABLE t1 ( a INT, b INT, KEY(a) );
+INSERT INTO t1 VALUES (NULL, 1), (NULL, 2);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE t1 ALL NULL NULL NULL NULL 2
+SELECT MIN(a), MIN(b) FROM t1;
+MIN(a) MIN(b)
+NULL 1
+CREATE TABLE t2( a INT, b INT, c INT, KEY(a, b) );
+INSERT INTO t2 ( a, b, c ) VALUES ( 1, NULL, 2 ), ( 1, 3, 4 ), ( 1, 4, 4 );
+EXPLAIN SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE t2 ref a a 5 const 2 Using where
+SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+MIN(b) MIN(c)
+3 2
+CREATE TABLE t3 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t3 VALUES (1, NULL, 1), (2, NULL, 2), (2, NULL, 2), (3, NULL, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+MIN(a) MIN(b)
+2 NULL
+CREATE TABLE t4 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t4 VALUES (1, 1, 1), (2, NULL, 2), (2, NULL, 2), (3, 1, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+MIN(a) MIN(b)
+2 NULL
+SELECT MIN(b), min(c) FROM t4 where a = 2;
+MIN(b) min(c)
+NULL 2
+CREATE TABLE t5( a INT, b INT, KEY( a, b) );
+INSERT INTO t5 VALUES( 1, 1 ), ( 1, 2 );
+EXPLAIN SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+MIN(a) MIN(b)
+1 1
+DROP TABLE t1, t2, t3, t4, t5;
End of 5.0 tests
--- 1.54/mysql-test/t/func_group.test 2007-02-27 09:01:57 +02:00
+++ 1.55/mysql-test/t/func_group.test 2007-04-20 11:56:26 +03:00
@@ -817,5 +817,38 @@ SELECT a,AVG(DISTINCT b) AS average FROM
DROP TABLE t1;
+#
+# Bug #27573: MIN() on an indexed column which is always NULL sets _other_
+# results to NULL
+#
+CREATE TABLE t1 ( a INT, b INT, KEY(a) );
+INSERT INTO t1 VALUES (NULL, 1), (NULL, 2);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t1;
+SELECT MIN(a), MIN(b) FROM t1;
+
+CREATE TABLE t2( a INT, b INT, c INT, KEY(a, b) );
+INSERT INTO t2 ( a, b, c ) VALUES ( 1, NULL, 2 ), ( 1, 3, 4 ), ( 1, 4, 4 );
+EXPLAIN SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+
+CREATE TABLE t3 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t3 VALUES (1, NULL, 1), (2, NULL, 2), (2, NULL, 2), (3, NULL, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+
+CREATE TABLE t4 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t4 VALUES (1, 1, 1), (2, NULL, 2), (2, NULL, 2), (3, 1, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+SELECT MIN(b), min(c) FROM t4 where a = 2;
+
+CREATE TABLE t5( a INT, b INT, KEY( a, b) );
+INSERT INTO t5 VALUES( 1, 1 ), ( 1, 2 );
+EXPLAIN SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+
+
+DROP TABLE t1, t2, t3, t4, t5;
+
###
--echo End of 5.0 tests
| Thread |
|---|
| • bk commit into 5.0 tree (mhansson:1.2432) BUG#27573 | mhansson | 20 Apr |
