The following query:

SELECT * FROM t1
WHERE (a) IN (
SELECT a
FROM t2
JOIN t3 ON b = a
);

returns

------

when executed with semijoin+materialization and

------

when executed otherwise (which seems to be the correct result).

Offending explain:

minimal switch: semijoin=on,materialization=on
full 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=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=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

bzr version-info
revision-id: <email address hidden>
date: 2011-10-17 03:42:56 -0700
build-date: 2011-10-18 13:05:59 +0300
revno: 3239
branch-nick: maria-5.3

test case:

CREATE TABLE t1 ( a int) ;
INSERT INTO t1 VALUES (19),(19),(19),(20),(20),(20),(20),(20),(20);

CREATE TABLE t2 ( b int NOT NULL , c int NOT NULL , KEY (b,c)) ;
INSERT INTO t2 VALUES (14,1),(15,1),(16,1),(17,1),(18,1),(19,1),(20,1);

CREATE TABLE t3 ( a int, d int) ;
INSERT INTO t3 VALUES (19,1),(7,1),(3,1),(3,1),(20,1),(3,1),(16,1),(17,1),(9,1),(4,1),(6,1),(15,1),(17,1);

SET SESSION optimizer_switch='semijoin=ON,materialization=ON';
SELECT * FROM t1
WHERE (a) IN (
SELECT a
FROM t2
JOIN t3 ON b = a );