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MDEV-5846 MySQL Bug #18144 - Cost with FORCE/USE index seems incorrect in some cases.

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This commit is contained in:
Sergei Golubchik 2014-03-20 23:27:08 +01:00
commit 3bb249612f
4 changed files with 69 additions and 2 deletions
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27
mysql-test/r/key.result
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@ -612,3 +612,30 @@ SELECT 1 as RES FROM t1 AS t1_outer WHERE
(SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) > 12;
RES
DROP TABLE t1;
#
# Bug#18144: Cost with FORCE/USE index seems incorrect in some cases.
#
# We are interested in showing that the cost for the last plan is higher
# than for the preceding two plans.
#
CREATE TABLE t1( a INT, b INT, KEY( a ) );
INSERT INTO t1 values (1, 2), (1, 3), (2, 3), (2, 4), (3, 4), (3, 5);
EXPLAIN SELECT a, SUM( b ) FROM t1 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 6 Using temporary; Using filesort
SHOW STATUS LIKE 'Last_query_cost';
Variable_name Value
Last_query_cost 9.212184
EXPLAIN SELECT a, SUM( b ) FROM t1 USE INDEX( a ) GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 6 Using temporary; Using filesort
SHOW STATUS LIKE 'Last_query_cost';
Variable_name Value
Last_query_cost 9.212184
EXPLAIN SELECT a, SUM( b ) FROM t1 FORCE INDEX( a ) GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL a 5 NULL 6
SHOW STATUS LIKE 'Last_query_cost';
Variable_name Value
Last_query_cost 14.199000
DROP TABLE t1;