Not repeatable with maria-5.3, mysql 5.1 . Not influenced by optimizer switches. The following query:

SELECT t3.b FROM t2 LEFT JOIN t3 ON ( 6 ) IN ( SELECT a FROM t1 );

returns t3.b = 0 even though the ON clause is FALSE and therefore there are no records to be joined between the two tables.

explain:

actual result:

mysql> SELECT t3.b FROM t2 LEFT JOIN t3 ON ( 6 ) IN ( SELECT a FROM t1 );
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expected result:

SELECT t3.b FROM t2 LEFT JOIN t3 ON ( 6 ) IN ( SELECT a FROM t1 );
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test case:

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 ( a int);
INSERT INTO t1 VALUES (0),(0);

DROP TABLE IF EXISTS t2;
CREATE TABLE t2 (b int);
INSERT INTO t2 VALUES (0);

DROP TABLE IF EXISTS t3;
CREATE TABLE t3 (b int);
INSERT INTO t3 VALUES (0);

SELECT t3.b FROM t2 LEFT JOIN t3 ON ( 6 ) IN ( SELECT a FROM t1 );

bzr version-info

revision-id: <email address hidden>
date: 2011-07-20 11:56:28 +0400
build-date: 2011-07-20 14:25:55 +0300
revno: 3123
branch-nick: maria-5.3

optimizer switch in effect:

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=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=off,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