Details
Major
Description
The following test case
SET optimizer_switch = 'derived_merge=on'; CREATE TABLE t1 (a INT) ENGINE=MyISAM; INSERT INTO t1 VALUES (1),(2); CREATE TABLE t2 (b INT) ENGINE=MyISAM; INSERT INTO t2 VALUES (3),(4); CREATE TABLE t3 (c INT) ENGINE=MyISAM; INSERT INTO t3 VALUES (5),(6); SELECT * FROM ( SELECT c FROM ( t1 INNER JOIN t2 ) RIGHT JOIN t3 ON a = c ) AS alias;
returns NULLs:
c ------ NULL NULL
If the subquery is executed separately, it returns not null values, which is the correct result:
c ------ 5 6
The problem was either introduced or made visible with the revision http://bazaar.launchpad.net/~maria-captains/maria/5.3/revision/3574:
revno: 3574 committer: sanja@montyprogram.com branch nick: work-maria-5.3-MDEV-486 timestamp: Wed 2012-09-05 23:23:58 +0300 message: MDEV-486 LP BUG#1010116 fix. Link view/derived table fields to a real table to check turning the table record to null row. Item_direct_view_ref wrapper now checks if table is turned to null row.
Reproducible on current maria/5.3, maria/5.5, maria/10.0.
MySQL 5.6 and MariaDB 5.2 return the correct result.
Minimal optimizer_switch: derived_merge=on.
Also reproducible with the default 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
EXPLAIN with the default optimizer_switch (also wrong result):
id select_type table type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t3 ALL NULL NULL NULL NULL 2 100.00 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 100.00 Using where; Using join buffer (flat, BNL join) 1 SIMPLE t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (incremental, BNL join) Warnings: Note 1003 select `test`.`t3`.`c` AS `c` from `test`.`t3` left join (`test`.`t1` join `test`.`t2`) on((`test`.`t1`.`a` = `test`.`t3`.`c`)) where 1
EXPLAIN with the minimal optimizer_switch (also wrong result):
id select_type table type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t3 ALL NULL NULL NULL NULL 2 100.00 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 100.00 Using where 1 SIMPLE t2 ALL NULL NULL NULL NULL 2 100.00 Warnings: Note 1003 select `test`.`t3`.`c` AS `c` from `test`.`t3` left join (`test`.`t1` join `test`.`t2`) on((`test`.`t1`.`a` = `test`.`t3`.`c`)) where 1
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MDEV-486 LP:1010116 - Incorrect query results in subqueries
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The problem is that TABLE_LIST::get_real_join_table incorrectly finds first table - t1 in "( t1 INNER JOIN t2 ) RIGHT JOIN t3". Correct first table is t3.
Fix committed for review.
Pushed to 5.3
Assigned to Sanja because it relates to his commit, please reassign if necessary.