database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-09-16 16:42:28 +03:00
Code Activity

Bug #25551: inconsistent behaviour in grouping NULL, depending on index type

Browse Source 
The optimizer takes away columns from GROUP BY/DISTINCT if they constitute
 all the parts of an unique index.
 However if some of the columns can contain NULLs this cannot be done 
(because an UNIQUE index can have multiple rows with NULL values).
 Fixed by not using UNIQUE indexes with nullable columns to remove
 grouping columns from GROUP BY/DISTINCT.


mysql-test/r/distinct.result:
  Bug #25551: inconsistent behaviour in grouping NULL, depending on index type
   - test case
mysql-test/t/distinct.test:
  Bug #25551: inconsistent behaviour in grouping NULL, depending on index type
   - test case
sql/sql_select.cc:
  Bug #25551: inconsistent behaviour in grouping NULL, depending on index type
   - UNIQUE NULL indices don't guarantee GROUP BY/DISTINCT.
This commit is contained in:
unknown
2007-01-31 10:18:26 +02:00
parent c6d4b94dd4
commit d01ec5e727
3 changed files with 52 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
mysql-test/r/distinct.result
View File

@@ -530,7 +530,8 @@ id select_type table type possible_keys key key_len ref rows Extra
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
CREATE TABLE t2(a INT, b INT, c INT, d INT, PRIMARY KEY (a,b));
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);
EXPLAIN SELECT DISTINCT a FROM t2;
id select_type table type possible_keys key key_len ref rows Extra
@@ -644,3 +645,26 @@ SELECT COUNT(*) FROM
COUNT(*)
2
DROP TABLE t1, t2;
CREATE TABLE t1 (a INT, UNIQUE (a));
INSERT INTO t1 VALUES (4),(null),(2),(1),(null),(3);
EXPLAIN SELECT DISTINCT a FROM t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL a 5 NULL 6 Using index
SELECT DISTINCT a FROM t1;
a
NULL
1
2
3
4
EXPLAIN SELECT a FROM t1 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 Using index
SELECT a FROM t1 GROUP BY a;
a
NULL
1
2
3
4
DROP TABLE t1;

17
mysql-test/t/distinct.test
View File

@@ -364,7 +364,8 @@ EXPLAIN SELECT a FROM t1 GROUP BY a;
EXPLAIN SELECT a,b FROM t1 GROUP BY a,b;
EXPLAIN SELECT DISTINCT a,b FROM t1 GROUP BY a,b;
CREATE TABLE t2(a INT, b INT, c INT, d INT, PRIMARY KEY (a,b));
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);
EXPLAIN SELECT DISTINCT a FROM t2;
EXPLAIN SELECT DISTINCT a,a FROM t2;
@@ -525,3 +526,17 @@ SELECT COUNT(*) FROM
(SELECT DISTINCT a FROM t2 WHERE a='oe' COLLATE latin1_german2_ci) dt;
DROP TABLE t1, t2;
#
# Bug #25551: inconsistent behaviour in grouping NULL, depending on index type
#
CREATE TABLE t1 (a INT, UNIQUE (a));
INSERT INTO t1 VALUES (4),(null),(2),(1),(null),(3);
EXPLAIN SELECT DISTINCT a FROM t1;
#result must have one row with NULL
SELECT DISTINCT a FROM t1;
EXPLAIN SELECT a FROM t1 GROUP BY a;
#result must have one row with NULL
SELECT a FROM t1 GROUP BY a;
DROP TABLE t1;