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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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5
.bzrignore
View file

@ -1345,3 +1345,8 @@ zlib/*.vcproj
debian/control
debian/defs.mk
include/abi_check
support-files/mysqld_multi.server
tests/bug25714
cscope.in.out
cscope.out
cscope.po.out

6
mysql-test/r/distinct.result
View file

@ -526,10 +526,10 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 3 Using index
EXPLAIN SELECT a,b FROM t1 GROUP BY a,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
EXPLAIN SELECT DISTINCT a,b FROM t1 GROUP BY a,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
CREATE TABLE t2(a INT, b INT NOT NULL, c INT NOT NULL, d INT,
PRIMARY KEY (a,b));
INSERT INTO t2 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4);
@ -554,7 +554,7 @@ id select_type table type possible_keys key key_len ref rows Extra
CREATE UNIQUE INDEX c_b_unq ON t2 (c,b);
EXPLAIN SELECT DISTINCT a,b,d FROM t2 GROUP BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using filesort
DROP TABLE t1,t2;
create table t1 (id int, dsc varchar(50));
insert into t1 values (1, "line number one"), (2, "line number two"), (3, "line number three");

49
mysql-test/r/group_by.result
View file

@ -1064,3 +1064,52 @@ select t1.f1,t.* from t1, t1 t group by 1;
ERROR 42000: 'test.t.f1' isn't in GROUP BY
drop table t1;
SET SQL_MODE = '';
CREATE TABLE t1(
a INT,
b INT NOT NULL,
c INT NOT NULL,
d INT,
UNIQUE KEY (c,b)
);
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 2 40
3 1 4
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 ALL NULL NULL NULL NULL 3 Using filesort
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;

49
mysql-test/r/innodb_mysql.result
View file

@ -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

27
mysql-test/t/group_by.test
View file

@ -788,3 +788,30 @@ select * from t1 group by f1, f2;
select t1.f1,t.* from t1, t1 t group by 1;
drop table t1;
SET SQL_MODE = '';
#
# Bug#30596: GROUP BY optimization gives wrong result order
#
CREATE TABLE t1(
a INT,
b INT NOT NULL,
c INT NOT NULL,
d INT,
UNIQUE KEY (c,b)
);
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;
SELECT c,b,d FROM t1 GROUP BY c,b,d;
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
EXPLAIN SELECT c,b,d FROM t1 ORDER BY c,b,d;
SELECT c,b,d FROM t1 ORDER BY c,b,d;
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b;
SELECT c,b,d FROM t1 GROUP BY c,b;
EXPLAIN SELECT c,b FROM t1 GROUP BY c,b;
SELECT c,b FROM t1 GROUP BY c,b;
DROP TABLE t1;

27
mysql-test/t/innodb_mysql.test
View file

@ -882,4 +882,31 @@ alter table t1 add index(a(1024));
show create table t1;
drop table t1;
#
# Bug#30596: GROUP BY optimization gives wrong result order
#
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;
SELECT c,b,d FROM t1 GROUP BY c,b,d;
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
EXPLAIN SELECT c,b,d FROM t1 ORDER BY c,b,d;
SELECT c,b,d FROM t1 ORDER BY c,b,d;
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b;
SELECT c,b,d FROM t1 GROUP BY c,b;
EXPLAIN SELECT c,b FROM t1 GROUP BY c,b;
SELECT c,b FROM t1 GROUP BY c,b;
DROP TABLE t1;
--echo End of 5.0 tests

8
sql/sql_select.cc
View file

@ -1030,6 +1030,14 @@ JOIN::optimize()
find_field_in_order_list,
(void *) group_list))
{
/*
We have found that grouping can be removed since groups correspond to
only one row anyway, but we still have to guarantee correct result
order. The line below effectively rewrites the query from GROUP BY
<fields> to ORDER BY <fields>. One exception is if skip_sort_order is
set (see above), then we can simply skip GROUP BY.
*/
order= skip_sort_order ? 0 : group_list;
group_list= 0;
group= 0;
}