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Fix for MDEV-4140

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Analysis:
Range analysis detects that the subquery is expensive and doesn't
build a range access method. Later, the applicability test for loose
scan doesn't take that into account, and builds a loose scan method
without a range scan on the min/max column. As a result loose scan
fetches the first key in each group, rather than the first key that
satisfies the condition on the min/max column.

Solution:
Since there is no SEL_ARG tree to be used for the min/max column,
it is not possible to use loose scan if the min/max column is compared
with an expensive scalar subquery. Make the test for loose scan
applicability to be in sync with the range analysis code by testing if
the min/max argument is compared with an expensive predicate.
This commit is contained in:
unknown 2013-02-13 11:58:16 +02:00
parent 3a0b25bb07
commit d4b1e8f31a
3 changed files with 59 additions and 1 deletions
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36
mysql-test/r/group_min_max.result
View file

@ -3243,4 +3243,40 @@ d 4
f 7
g 8
drop table t1;
#
# MDEV-4140 Wrong result with GROUP BY + multipart key + MIN/MAX loose scan and a subquery
#
CREATE TABLE t1 (a int, b int, KEY (b, a)) ;
INSERT INTO t1 VALUES (0,99),(9,99),(4,0),(7,0),(99,0),(7,0),(8,0),(99,0),(1,0);
CREATE TABLE t2 (c int) ;
INSERT INTO t2 VALUES (0),(1);
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > 0 GROUP BY b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL b 10 NULL 10 Using where; Using index for group-by
SELECT MIN(a), b FROM t1 WHERE a > 0 GROUP BY b;
MIN(a) b
1 0
9 99
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT c FROM t2 WHERE c = 0 ) GROUP BY b;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 index NULL b 10 NULL 9 Using where; Using index
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT c FROM t2 WHERE c = 0 ) GROUP BY b;
MIN(a) b
1 0
9 99
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT min(c) FROM t2, t1 t1a, t1 t1b WHERE c = 0 ) GROUP BY b;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 index NULL b 10 NULL 9 Using where; Using index
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
2 SUBQUERY t1a index NULL b 10 NULL 9 Using index; Using join buffer (flat, BNL join)
2 SUBQUERY t1b index NULL b 10 NULL 9 Using index; Using join buffer (incremental, BNL join)
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT min(c) FROM t2, t1 t1a, t1 t1b WHERE c = 0 ) GROUP BY b;
MIN(a) b
1 0
9 99
drop table t1, t2;
End of 5.3 tests

22
mysql-test/t/group_min_max.test
View file

@ -1239,4 +1239,26 @@ SELECT b, min(a) FROM t1 WHERE (a > '0' AND (a > '1' OR b = 'd')) GROUP BY b;
drop table t1;
--echo #
--echo # MDEV-4140 Wrong result with GROUP BY + multipart key + MIN/MAX loose scan and a subquery
--echo #
CREATE TABLE t1 (a int, b int, KEY (b, a)) ;
INSERT INTO t1 VALUES (0,99),(9,99),(4,0),(7,0),(99,0),(7,0),(8,0),(99,0),(1,0);
CREATE TABLE t2 (c int) ;
INSERT INTO t2 VALUES (0),(1);
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > 0 GROUP BY b;
SELECT MIN(a), b FROM t1 WHERE a > 0 GROUP BY b;
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT c FROM t2 WHERE c = 0 ) GROUP BY b;
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT c FROM t2 WHERE c = 0 ) GROUP BY b;
# this test is for 5.5 to ensure that the subquery is expensive
EXPLAIN
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT min(c) FROM t2, t1 t1a, t1 t1b WHERE c = 0 ) GROUP BY b;
SELECT MIN(a), b FROM t1 WHERE a > ( SELECT min(c) FROM t2, t1 t1a, t1 t1b WHERE c = 0 ) GROUP BY b;
drop table t1, t2;
--echo End of 5.3 tests

2
sql/opt_range.cc
View file

@ -12236,7 +12236,7 @@ check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
&has_min_max, &has_other))
DBUG_RETURN(FALSE);
}
else if (cur_arg->const_item())
else if (cur_arg->const_item() && !cur_arg->is_expensive())
{
/*
For predicates of the form "const OP expr" we also have to check 'expr'