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Fixed bug #25407.

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The bug could cause choosing a sub-optimal execution plan for 
a single-table query if a unique index with many null keys were 
defined for the table. 
It happened because the code of the check_quick_keys function 
made an assumption that any key may occur in an unique index 
only once. Yet this is not true for keys with nulls that may 
have multiple occurrences in the index.
This commit is contained in:
igor@olga.mysql.com
2007-01-31 19:31:36 -08:00
parent 8760182170
commit 710136217b
4 changed files with 173 additions and 3 deletions
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86
mysql-test/r/select.result
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@ -3642,3 +3642,89 @@ INSERT into t1 values (1), (2), (3);
SELECT * FROM t1 LIMIT 2, -1;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-1' at line 1
DROP TABLE t1;
CREATE TABLE t1 (
ID_with_null int NULL,
ID_better int NOT NULL,
INDEX idx1 (ID_with_null),
INDEX idx2 (ID_better)
);
INSERT INTO t1 VALUES (1,1), (2,1), (null,3), (null,3), (null,3), (null,3);
INSERT INTO t1 SELECT * FROM t1 WHERE ID_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID_with_null IS NULL;
SELECT COUNT(*) FROM t1 WHERE ID_with_null IS NULL;
COUNT(*)
128
SELECT COUNT(*) FROM t1 WHERE ID_better=1;
COUNT(*)
2
EXPLAIN SELECT * FROM t1 WHERE ID_better=1 AND ID_with_null IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
DROP INDEX idx1 ON t1;
CREATE UNIQUE INDEX idx1 ON t1(ID_with_null);
EXPLAIN SELECT * FROM t1 WHERE ID_better=1 AND ID_with_null IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
DROP TABLE t1;
CREATE TABLE t1 (
ID1_with_null int NULL,
ID2_with_null int NULL,
ID_better int NOT NULL,
INDEX idx1 (ID1_with_null, ID2_with_null),
INDEX idx2 (ID_better)
);
INSERT INTO t1 VALUES (1,1,1), (2,2,1), (3,null,3), (null,3,3), (null,null,3),
(3,null,3), (null,3,3), (null,null,3), (3,null,3), (null,3,3), (null,null,3);
INSERT INTO t1 SELECT * FROM t1 WHERE ID1_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID2_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID1_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID2_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID1_with_null IS NULL;
INSERT INTO t1 SELECT * FROM t1 WHERE ID2_with_null IS NULL;
SELECT COUNT(*) FROM t1 WHERE ID1_with_null IS NULL AND ID2_with_null=3;
COUNT(*)
24
SELECT COUNT(*) FROM t1 WHERE ID1_with_null=3 AND ID2_with_null IS NULL;
COUNT(*)
24
SELECT COUNT(*) FROM t1 WHERE ID1_with_null IS NULL AND ID2_with_null IS NULL;
COUNT(*)
192
SELECT COUNT(*) FROM t1 WHERE ID_better=1;
COUNT(*)
2
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null IS NULL AND ID2_with_null=3 ;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null=3 AND ID2_with_null=3 IS NULL ;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null IS NULL AND ID2_with_null IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
DROP INDEX idx1 ON t1;
CREATE UNIQUE INDEX idx1 ON t1(ID1_with_null,ID2_with_null);
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null IS NULL AND ID2_with_null=3 ;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null=3 AND ID2_with_null IS NULL ;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null IS NULL AND ID2_with_null IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
EXPLAIN SELECT * FROM t1
WHERE ID_better=1 AND ID1_with_null IS NULL AND
(ID2_with_null=1 OR ID2_with_null=2);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref idx1,idx2 idx2 4 const 1 Using where
DROP TABLE t1;