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The following query
SELECT STRAIGHT_JOIN * FROM t1 AS alias1, t1 AS alias2
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WHERE EXISTS ( SELECT 1 FROM t1 WHERE b < alias2.b AND a = alias1.a )
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on the test data produces 4 rows if it's run with exists_to_in=on, and 1 row otherwise. 1 row is the correct result.
bzr version-info
revision-id: sanja@askmonty.org-20120718105902-imt07qp0v913sqa4
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date: 2012-07-18 13:59:02 +0300
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build-date: 2012-07-19 21:33:12 +0400
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revno: 3466
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Reproducible with MyISAM, Aria, InnoDB.
Minimal optimizer_switch:
exists_to_in=on,in_to_exists=on
Full optimizer_switch (default + exists_to_in=on):
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=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,extended_keys=off,exists_to_in=on
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EXPLAIN with the minimal optimizer_switch (exists_to_in=on,in_to_exists=on, everything else OFF):
id select_type table type possible_keys key key_len ref rows filtered Extra
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1 PRIMARY alias1 ALL NULL NULL NULL NULL 2 100.00 Using where
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1 PRIMARY alias2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
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2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 100.00 Using where
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Warnings:
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Note 1276 Field or reference 'test.alias2.b' of SELECT #2 was resolved in SELECT #1
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Note 1276 Field or reference 'test.alias1.a' of SELECT #2 was resolved in SELECT #1
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Note 1003 select straight_join `test`.`alias1`.`a` AS `a`,`test`.`alias1`.`b` AS `b`,`test`.`alias2`.`a` AS `a`,`test`.`alias2`.`b` AS `b` from `test`.`t1` `alias1` join `test`.`t1` `alias2` where <in_optimizer>(`test`.`alias1`.`a`,<exists>(select `test`.`t1`.`a` from `test`.`t1` where ((`test`.`t1`.`b` < `test`.`alias2`.`b`) and (<cache>(`test`.`alias1`.`a`) = `test`.`t1`.`a`))))
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EXPLAIN with the default optimizer_switch + exists_to_in=on:
id select_type table type possible_keys key key_len ref rows filtered Extra
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1 PRIMARY alias1 ALL NULL NULL NULL NULL 2 100.00 Using where
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1 PRIMARY alias2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
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2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 100.00 Using where
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Warnings:
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Note 1276 Field or reference 'test.alias2.b' of SELECT #2 was resolved in SELECT #1
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Note 1276 Field or reference 'test.alias1.a' of SELECT #2 was resolved in SELECT #1
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Note 1003 select straight_join `test`.`alias1`.`a` AS `a`,`test`.`alias1`.`b` AS `b`,`test`.`alias2`.`a` AS `a`,`test`.`alias2`.`b` AS `b` from `test`.`t1` `alias1` join `test`.`t1` `alias2` where <expr_cache><`test`.`alias1`.`a`,`test`.`alias2`.`b`>(<in_optimizer>(`test`.`alias1`.`a`,<exists>(select `test`.`t1`.`a` from `test`.`t1` where ((`test`.`t1`.`b` < `test`.`alias2`.`b`) and (<cache>(`test`.`alias1`.`a`) = `test`.`t1`.`a`)))))
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Test case:
SET optimizer_switch = 'exists_to_in=on,in_to_exists=on';
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CREATE TABLE t1 (a INT, b VARCHAR(1) NOT NULL);
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INSERT INTO t1 VALUES (1,'s'),(2,'e');
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SELECT STRAIGHT_JOIN * FROM t1 AS alias1, t1 AS alias2
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WHERE EXISTS ( SELECT 1 FROM t1 WHERE b < alias2.b AND a = alias1.a );
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Expected result:
Actual result:
a b a b
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1 s 1 s
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2 e 1 s
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1 s 2 e
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2 e 2 e
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Please note that removing 'NOT NULL' option from the column definition makes the same query return an empty result, which is also incorrect.
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