Details
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Type:
Bug
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Status: Closed
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Priority:
Critical
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
The following query
SELECT *
FROM t1 RIGHT JOIN t2 ON ( a = c )
WHERE ( b, c ) IN
( SELECT b, c FROM t2 )
on the test data returns wrong result (less rows and in one row a NULL instead of a value) with join_cache_level>2, and correct result otherwise.
bzr version-info
revision-id: <email address hidden>
date: 2012-02-16 20:15:57 +0400
build-date: 2012-02-17 21:10:34 +0400
revno: 3424
EXPLAIN with join_cache_level=3 (wrong result):
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t2 ALL b NULL NULL NULL 3 100.00
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 10 func,func 1 100.00
1 PRIMARY t1 hash_index a #hash#a:a 4:4 test.t2.c 4 50.00 Using where; Using join buffer (flat, BNLH join)
2 MATERIALIZED t2 ALL b NULL NULL NULL 3 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` semi join (`test`.`t2`) left join `test`.`t1` on(((`test`.`t1`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`c` is not null))) where 1
EXPLAIN with join_cache_level=2 (correct result):
d select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t2 ALL b NULL NULL NULL 3 100.00
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 10 func,func 1 100.00
1 PRIMARY t1 ref a a 4 test.t2.c 2 100.00 Using where; Using index
2 MATERIALIZED t2 ALL b NULL NULL NULL 3 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` semi join (`test`.`t2`) left join `test`.`t1` on(((`test`.`t1`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`c` is not null))) where 1
Minimal optimizer_switch: materialization=on,semijoin=on,join_cache_hashed=on
(and join_cache_level>=3)
Full 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=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on
Test case:
SET optimizer_switch = 'materialization=on,semijoin=on,join_cache_hashed=on';
- join_cache_level >= 3
SET SESSION join_cache_level = 3;
CREATE TABLE t1 ( a VARCHAR(1), KEY(a) );
INSERT INTO t1 VALUES ('v'),('v'),('s'),('j');
CREATE TABLE t2 ( b VARCHAR(1), c VARCHAR(1), KEY(b) );
INSERT INTO t2 VALUES ('v','v'),('w','w'),('t','t');
SELECT *
FROM t1 RIGHT JOIN t2 ON ( a = c )
WHERE ( b, c ) IN
( SELECT b, c FROM t2 );
- End of test case
- Expected result:
- a b c
- -----------------
- v v v
- v v v
- NULL w w
- NULL t t
- Actual result:
- a b c
- -----------------
- NULL v v
- NULL w w
- NULL t t
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Re: Wrong result (missing rows, wrong values) with materialization+semijoin+join_cache_hashed, join_cache_level>2, RIGHT JOIN, IN subquery
The first plan shows that the key is copied from table t, rather then from the materialized table. The last record in table t is ('t','t'). So the key to access table t1 always is built over this record. This explains why we have a wrong result for the first plan.
Re: Wrong result (missing rows, wrong values) with materialization+semijoin+join_cache_hashed, join_cache_level>2, RIGHT JOIN, IN subquery
Fix released with 5.3.5-ga.
Launchpad bug id: 934342
Re: Wrong result (missing rows, wrong values) with materialization+semijoin+join_cache_hashed, join_cache_level>2, RIGHT JOIN, IN subquery
The bug is reproducible with LEFT JOIN as well.
With Elena's settings and
set join_cache_level = 6
I get the following execution plan:
MariaDB [test]> EXPLAIN EXTENDED SELECT * FROM t2 LEFT JOIN t1 ON ( a = c ) WHERE ( b, c ) IN ( SELECT b, c FROM t2 t );
---
--------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------I get a wrong result set when executing by this plan.
If I use
set join_cache_level = 0;
I get the execution plan:
MariaDB [test]> EXPLAIN EXTENDED SELECT * FROM t2 LEFT JOIN t1 ON ( a = c ) WHERE ( b, c ) IN ( SELECT b, c FROM t2 t );
---
--------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------4 rows in set, 1 warning (0.00 sec)
I get the right result set when executing by this plan.
The plans differ only in line 3:
the first plan uses test.t.c to build the key to access table t1,
while the second plan uses test.t2.c for this purpose.