2012-04-05 09:43:32.947833+00:00
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https://bugs.launchpad.net/bugs/825075
Philip Stoev
Timour Katchaounov
Maria 5.2
Wrong result with GROUP BY + multipart key + MIN/MAX loose scan
Confirmed
High
2011-08-12 09:20:57.394133+00:00
( SELECT a FROM t2 WHERE a = 0 )
GROUP BY b;
does not return as many rows as if the subquery is replaced with a constant.
explain:
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 range NULL b 10 NULL 10 Using where; Using index for group-by
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
optimizer switch:
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on
test case:
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 (a int) ;
INSERT INTO t2 VALUES (0),(1);
SELECT MIN(a), b
FROM t1
WHERE a > ( SELECT a FROM t2 WHERE a = 0 )
GROUP BY b;
returns:
MIN(a) b
1 0
SELECT MIN(a), b
FROM t1
WHERE a > 0
GROUP BY b;
returns:
MIN(a) b
1 0
9 99
bzr version-info:
revision-id:
date: 2011-08-11 22:34:41 -0700
build-date: 2011-08-12 12:20:36 +0300
revno: 3151
branch-nick: maria-5.3
Repeatable on maria-5.3. Not repeatable on maria-5.2, mysql-5.5. Not repeatable with other subquery operators. Does not involve NULLs or constant tables.]]>
bug
Philip Stoev
added bug
maria: milestone
Philip Stoev
maria: assignee
Timour Katchaounov
maria: milestone
Igor Babaev
maria: importance
Oleksandr "Sanja" Byelkin
maria: importance
Oleksandr "Sanja" Byelkin
maria: milestone
Oleksandr "Sanja" Byelkin
maria: status
Oleksandr "Sanja" Byelkin
maria: importance
Oleksandr "Sanja" Byelkin
maria: milestone
Oleksandr "Sanja" Byelkin
maria: assignee
Sergey Petrunia
maria: status
Timour Katchaounov
summary
Timour Katchaounov
maria: status
Timour Katchaounov
maria: status
Timour Katchaounov
maria: status
Timour Katchaounov
summary
Elena Stepanova
tags
Elena Stepanova
maria: status
Timour Katchaounov
Philip Stoev
( SELECT a FROM t2 WHERE a = 0 )
GROUP BY b;
does not return as many rows as if the subquery is replaced with a constant.
explain:
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 range NULL b 10 NULL 10 Using where; Using index for group-by
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
optimizer switch:
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on
test case:
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 (a int) ;
INSERT INTO t2 VALUES (0),(1);
SELECT MIN(a), b
FROM t1
WHERE a > ( SELECT a FROM t2 WHERE a = 0 )
GROUP BY b;
returns:
MIN(a) b
1 0
SELECT MIN(a), b
FROM t1
WHERE a > 0
GROUP BY b;
returns:
MIN(a) b
1 0
9 99
bzr version-info:
revision-id: igor@askmonty.org-20110812053441-rrax06kfhjlmkq45
date: 2011-08-11 22:34:41 -0700
build-date: 2011-08-12 12:20:36 +0300
revno: 3151
branch-nick: maria-5.3
Repeatable on maria-5.3. Not repeatable on maria-5.2, mysql-5.5. Not repeatable with other subquery operators. Does not involve NULLs or constant tables.]]>
Oleksandr "Sanja" Byelkin
(select `test`.`t2`.`a` from `test`.`t2` where (`test`.`t2`.`a` = 0))) group by `test`.`t1`.`b`
If reduce test suite table to INSERT INTO t1 VALUES (0,99),(9,99),(4,0),(7,0),(99,0),(7,0),(8,0),(99,0),(1,0); it works correctly with other explain:
+id select_type table type possible_keys key key_len ref rows filtered Extra
+1 PRIMARY t1 index NULL b 10 NULL 6 100.00 Using where; Using index
+2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 100.00 Using where
+Warnings:
+Note 1003 select min(`test`.`t1`.`a`) AS `MIN(a)`,`test`.`t1`.`b` AS `b` from `test`.`t1` where (`test`.`t1`.`a` > (select `test`.`t2`.`a` from `test`.`t2` where (`test`.`t2`.`a` = 0))) group by `test`.`t1`.`b`]]>
Philip Stoev
Philip Stoev
Oleksandr "Sanja" Byelkin
Sergey Petrunia
Timour Katchaounov