Commit e093fb1f authored by evgen@moonbone.local's avatar evgen@moonbone.local
Browse files

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 used
keyparts forms a prefix of the index.
parent 21a9d6a6

mysql-test/r/group_min_max.result

+10 −0
Original line number Diff line number Diff line
@@ -2002,3 +2002,13 @@ a count(a) 
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;

mysql-test/t/group_min_max.test

+10 −0
Original line number Diff line number Diff line
@@ -693,3 +693,13 @@ create table t1(a int, key(a)) engine=innodb; 
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;

sql/opt_range.cc

+13 −0
Original line number Diff line number Diff line
@@ -7197,6 +7197,7 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree) 
    {

      select_items_it.rewind();

      cur_used_key_parts.clear_all();

      uint max_key_part= 0;

      while ((item= select_items_it++))

      {

        item_field= (Item_field*) item; /* (SA5) already checked above. */
@@ -7214,7 +7215,19 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree) 
        cur_group_prefix_len+= cur_part->store_length;

        cur_used_key_parts.set_bit(key_part_nr);

        ++cur_group_key_parts;

        max_key_part= max(max_key_part,key_part_nr);

      }

      /*

        Check that used key parts forms a prefix of the index.

        To check this we compare bits in all_parts and cur_parts.

        all_parts have all bits set from 0 to (max_key_part-1).

        cur_parts have bits set for only used keyparts.

      */

      ulonglong all_parts, cur_parts;

      all_parts= (1<<max_key_part) - 1;

      cur_parts= cur_used_key_parts.to_ulonglong() >> 1;

      if (all_parts != cur_parts)

        goto next_index;

    }

    else

      DBUG_ASSERT(FALSE);