bk commit into 5.0 tree (evgen:1.1974) BUG#13293

[eugene]

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ChangeSet
  1.1974 05/11/19 00:05:58 evgen@stripped +3 -0
  Fix bug#13293 Wrongly used index results in endless loop.
  
  Loose index scan using only second part of multipart index was choosen, which
  results in creating wrong keys and endless loop.
  
  get_best_group_min_max() now allows loose index scan for distinct only if all
  keyparts of index are used and all fields are covered by index.

  mysql-test/r/group_min_max.result
    1.18 05/11/18 23:59:13 evgen@stripped +10 -0
    Test case for bug#13293 Wrongly used index results in endless loop.

  mysql-test/t/group_min_max.test
    1.16 05/11/18 23:58:50 evgen@stripped +10 -0
     Test case for bug#13293 Wrongly used index results in endless loop.

  sql/opt_range.cc
    1.197 05/11/18 23:56:24 evgen@stripped +10 -3
    Fix bug #13293 Wrongly used index results in endless loop.
    get_best_group_min_max() now allows loose index scan for distinct only if all
    keyparts of index are used and all fields are covered by index.
    

# 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:	evgen
# Host:	moonbone.local
# Root:	/work/13293-bug-5.0-mysql

--- 1.196/sql/opt_range.cc	2005-11-03 17:42:03 +03:00
+++ 1.197/sql/opt_range.cc	2005-11-18 23:56:24 +03:00
@@ -6916,9 +6916,9 @@
     SA5. The select list in DISTINCT queries should not contain expressions.
     GA1. If Q has a GROUP BY clause, then GA is a prefix of I. That is, if
          G_i = A_j => i = j.
-    GA2. If Q has a DISTINCT clause, then there is a permutation of SA that
-         forms a prefix of I. This permutation is used as the GROUP clause
-         when the DISTINCT query is converted to a GROUP query.
+    GA2. If Q has a DISTINCT clause, then there is a permutation of SA.
+         This permutation is used as the GROUP clause when the DISTINCT
+         query is converted to a GROUP query.
     GA3. The attributes in GA may participate in arbitrary predicates, divided
          into two groups:
          - RNG(G_1,...,G_q ; where q <= k) is a range condition over the
@@ -7208,6 +7208,13 @@
         cur_used_key_parts.set_bit(key_part_nr);
         ++cur_group_key_parts;
       }
+      /*
+        For loose index scan being applicable for distinct all fields
+        should be covered by index and all parts of index should be used.
+      */
+      if (cur_group_key_parts != join->fields_list.elements ||
+          cur_group_key_parts != cur_index_info->key_parts)
+        goto next_index;
     }
     else
       DBUG_ASSERT(FALSE);

--- 1.17/mysql-test/r/group_min_max.result	2005-09-25 17:43:52 +04:00
+++ 1.18/mysql-test/r/group_min_max.result	2005-11-18 23:59:13 +03:00
@@ -2002,3 +2002,13 @@
 1	1
 NULL	1
 drop table t1;
+create table t1 (f1 int, f2 char(1), primary key(f1,f2)) engine=innodb;
+insert into t1 values ( 1,"e"),(2,"a"),( 3,"c"),(4,"d");
+alter table t1 drop primary key, add primary key (f2, f1);
+explain select distinct f1 a, f1 b from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	PRIMARY	5	NULL	4	Using index; Using temporary
+explain select distinct f1, f2 from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	NULL	PRIMARY	5	NULL	3	Using index for group-by; Using temporary
+drop table t1;

--- 1.15/mysql-test/t/group_min_max.test	2005-09-25 17:43:53 +04:00
+++ 1.16/mysql-test/t/group_min_max.test	2005-11-18 23:58:50 +03:00
@@ -693,3 +693,13 @@
 insert into t1 values(1);
 select a, count(a) from t1 group by a with rollup;
 drop table t1;
+
+#
+# Bug #13293 Wrongly used index results in endless loop.
+#
+create table t1 (f1 int, f2 char(1), primary key(f1,f2)) engine=innodb;
+insert into t1 values ( 1,"e"),(2,"a"),( 3,"c"),(4,"d");
+alter table t1 drop primary key, add primary key (f2, f1);
+explain select distinct f1 a, f1 b from t1;
+explain select distinct f1, f2 from t1;
+drop table t1;