From a4d5d9204dcf82b45f86008f3f2a9e2414732329 Mon Sep 17 00:00:00 2001 From: "mhansson/martin@linux-st28.site" <> Date: Mon, 27 Aug 2007 17:33:41 +0200 Subject: [PATCH] Bug #30596 GROUP BY optimization gives wrong result order 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. --- .bzrignore | 5 ++++ mysql-test/r/distinct.result | 6 ++-- mysql-test/r/group_by.result | 49 ++++++++++++++++++++++++++++++++ mysql-test/r/innodb_mysql.result | 49 ++++++++++++++++++++++++++++++++ mysql-test/t/group_by.test | 27 ++++++++++++++++++ mysql-test/t/innodb_mysql.test | 27 ++++++++++++++++++ sql/sql_select.cc | 8 ++++++ 7 files changed, 168 insertions(+), 3 deletions(-) diff --git a/.bzrignore b/.bzrignore index 759ca4a20bf..35f5199be3c 100644 --- a/.bzrignore +++ b/.bzrignore @@ -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 diff --git a/mysql-test/r/distinct.result b/mysql-test/r/distinct.result index 8525e0f19e4..8cfe5aa78b5 100644 --- a/mysql-test/r/distinct.result +++ b/mysql-test/r/distinct.result @@ -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"); diff --git a/mysql-test/r/group_by.result b/mysql-test/r/group_by.result index d4ffbe43a91..053c2901509 100644 --- a/mysql-test/r/group_by.result +++ b/mysql-test/r/group_by.result @@ -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; diff --git a/mysql-test/r/innodb_mysql.result b/mysql-test/r/innodb_mysql.result index 63e25b7aa1e..82955af4c8a 100644 --- a/mysql-test/r/innodb_mysql.result +++ b/mysql-test/r/innodb_mysql.result @@ -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 diff --git a/mysql-test/t/group_by.test b/mysql-test/t/group_by.test index 91e69f9db34..b7c28cada46 100644 --- a/mysql-test/t/group_by.test +++ b/mysql-test/t/group_by.test @@ -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; diff --git a/mysql-test/t/innodb_mysql.test b/mysql-test/t/innodb_mysql.test index adcfec68d3e..949e602a299 100644 --- a/mysql-test/t/innodb_mysql.test +++ b/mysql-test/t/innodb_mysql.test @@ -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 diff --git a/sql/sql_select.cc b/sql/sql_select.cc index ac8dc84f118..4be542975b5 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -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 + to ORDER BY . 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; }