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Bug #43029: FORCE INDEX FOR ORDER BY is ignored when join

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buffering is used

FORCE INDEX FOR ORDER BY now prevents the optimizer from 
using join buffering. As a result the optimizer can use
indexed access on the first table and doesn't need to 
sort the complete resultset at the end of the statement.
This commit is contained in:
Georgi Kodinov
2009-10-07 18:03:42 +03:00
parent 9226c847f5
commit 1a48dd4e2b
8 changed files with 116 additions and 12 deletions
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31
mysql-test/r/order_by.result
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@ -1557,3 +1557,34 @@ a
2001
1991
DROP TABLE t1;
#
# Bug #43029: FORCE INDEX FOR ORDER BY is ignored when join buffering
# is used
#
CREATE TABLE t1 (a INT, b INT, KEY (a));
INSERT INTO t1 VALUES (0, NULL), (1, NULL), (2, NULL), (3, NULL);
INSERT INTO t1 SELECT a+4, b FROM t1;
INSERT INTO t1 SELECT a+8, b FROM t1;
CREATE TABLE t2 (a INT, b INT);
INSERT INTO t2 VALUES (0,NULL), (1,NULL), (2,NULL), (3,NULL), (4,NULL);
INSERT INTO t2 SELECT a+4, b FROM t2;
# shouldn't have "using filesort"
EXPLAIN
SELECT * FROM t1 FORCE INDEX FOR ORDER BY (a), t2 WHERE t1.a < 2 ORDER BY t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 2 Using where
1 SIMPLE t2 ALL NULL NULL NULL NULL 10
# should have "using filesort"
EXPLAIN
SELECT * FROM t1 USE INDEX FOR ORDER BY (a), t2 WHERE t1.a < 2 ORDER BY t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 2 Using where; Using temporary; Using filesort
1 SIMPLE t2 ALL NULL NULL NULL NULL 10 Using join buffer
# should have "using filesort"
EXPLAIN
SELECT * FROM t1 FORCE INDEX FOR JOIN (a), t2 WHERE t1.a < 2 ORDER BY t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 2 Using where; Using temporary; Using filesort
1 SIMPLE t2 ALL NULL NULL NULL NULL 10 Using join buffer
DROP TABLE t1, t2;
End of 5.1 tests