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Bug #30596 GROUP BY optimization gives wrong result order

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The optimization that uses a unique index to remove GROUP BY, did not 
ensure that the index was actually used, thus violating the ORDER BY
that is impled by GROUP BY.
Fixed by replacing GROUP BY with ORDER BY if the GROUP BY clause contains
a unique index. In case GROUP BY ... ORDER BY null is used, GROUP BY is
simply removed.
This commit is contained in:
mhansson/martin@linux-st28.site
2007-08-27 17:33:41 +02:00
parent c40fe57fb5
commit a4d5d9204d
7 changed files with 168 additions and 3 deletions
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49
mysql-test/r/innodb_mysql.result
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@ -1047,4 +1047,53 @@ t1 CREATE TABLE `t1` (
KEY `a` (`a`(255))
) ENGINE=InnoDB DEFAULT CHARSET=utf8
drop table t1;
CREATE TABLE t1(
a INT,
b INT NOT NULL,
c INT NOT NULL,
d INT,
UNIQUE KEY (c,b)
) engine=innodb;
INSERT INTO t1 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4);
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT c,b,d FROM t1 GROUP BY c,b,d;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b,d FROM t1 ORDER BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT c,b,d FROM t1 ORDER BY c,b,d;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL c 8 NULL 3
SELECT c,b,d FROM t1 GROUP BY c,b;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b FROM t1 GROUP BY c,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL c 8 NULL 3 Using index
SELECT c,b FROM t1 GROUP BY c,b;
c b
1 1
3 1
3 2
DROP TABLE t1;
End of 5.0 tests