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';

1. 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 );

1. End of test case

1. Expected result:
2. a b c
3. -----------------
4. v v v
5. v v v
6. NULL w w
7. NULL t t

1. Actual result:
2. a b c
3. -----------------
4. NULL v v
5. NULL w w
6. NULL t t