mirror/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-01-17 12:32:27 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

Fixed bug #25602. A query with DISTINCT in the select list to which

Browse source 
the loose scan optimization for grouping queries was applied returned 
a wrong result set when the query was used with the SQL_BIG_RESULT
option.

The SQL_BIG_RESULT option forces to use sorting algorithm for grouping
queries instead of employing a suitable index. The current loose scan
optimization is applied only for one table queries when the suitable
index is covering. It does not make sense to use sort algorithm in this
case. However the create_sort_index function does not take into account
the possible choice of the loose scan to implement the DISTINCT operator
which makes sorting unnecessary. Moreover the current implementation of
the loose scan for queries with distinct assumes that sorting will
never happen. Thus in this case create_sort_index should not call
the function filesort.


mysql-test/r/group_min_max.result:
  Added a test case for bug #25602.
mysql-test/t/group_min_max.test:
  Added a test case for bug #25602.
This commit is contained in:
unknown 2007-06-23 23:33:55 -07:00
parent f3940ebaf0
commit e009b764b9
3 changed files with 49 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
mysql-test/r/group_min_max.result
View file

@ -2286,3 +2286,24 @@ Variable_name Value
Handler_read_key 8
Handler_read_next 1
DROP TABLE t1,t2,t3;
CREATE TABLE t1 (a int, INDEX idx(a));
INSERT INTO t1 VALUES
(4), (2), (1), (2), (4), (2), (1), (4),
(4), (2), (1), (2), (2), (4), (1), (4);
EXPLAIN SELECT DISTINCT(a) FROM t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL idx 5 NULL 9 Using index for group-by
SELECT DISTINCT(a) FROM t1;
a
1
2
4
EXPLAIN SELECT SQL_BIG_RESULT DISTINCT(a) FROM t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL idx 5 NULL 9 Using index for group-by
SELECT SQL_BIG_RESULT DISTINCT(a) FROM t1;
a
1
2
4
DROP TABLE t1;

22
mysql-test/t/group_min_max.test
View file

@ -870,3 +870,25 @@ DELETE FROM t3 WHERE (SELECT (SELECT MAX(b) FROM t1 GROUP BY a HAVING a < 2) x
SHOW STATUS LIKE 'handler_read__e%';
DROP TABLE t1,t2,t3;
#
# Bug#25602: queries with DISTINCT and SQL_BIG_RESULT hint
# for which loose scan optimization is applied
#
CREATE TABLE t1 (a int, INDEX idx(a));
INSERT INTO t1 VALUES
(4), (2), (1), (2), (4), (2), (1), (4),
(4), (2), (1), (2), (2), (4), (1), (4);
EXPLAIN SELECT DISTINCT(a) FROM t1;
SELECT DISTINCT(a) FROM t1;
EXPLAIN SELECT SQL_BIG_RESULT DISTINCT(a) FROM t1;
SELECT SQL_BIG_RESULT DISTINCT(a) FROM t1;
DROP TABLE t1;

8
sql/sql_select.cc
View file

@ -12552,10 +12552,14 @@ create_sort_index(THD *thd, JOIN *join, ORDER *order,
/*
When there is SQL_BIG_RESULT do not sort using index for GROUP BY,
and thus force sorting on disk.
and thus force sorting on disk unless a group min-max optimization
is going to be used as it is applied now only for one table queries
with covering indexes.
*/
if ((order != join->group_list ||
!(join->select_options & SELECT_BIG_RESULT)) &&
!(join->select_options & SELECT_BIG_RESULT) ||
select && select->quick &&
select->quick->get_type() == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX) &&
test_if_skip_sort_order(tab,order,select_limit,0))
DBUG_RETURN(0);
for (ORDER *ord= join->order; ord; ord= ord->next)