The query below returns no rows in maria-5.3 even though the subquery returns an empty result and therefore the ALL predicate should evaluate to TRUE. Not influenced by optimizer_switches. Not repeatable with maria-5.2, mysql-5.1. Also please check the = ALL form, as it appears to return an incorrect result as well .

test case:

CREATE TABLE t1 (a int);
INSERT INTO t1 VALUES (0);

CREATE TABLE t2 ( b int, KEY (b) );
INSERT INTO t2 VALUES (0);

CREATE TABLE t3 ( c int) ;
INSERT INTO t3 VALUES (6);

CREATE TABLE t4 (d int) ;

SELECT * FROM t1
WHERE t1.a < ALL (
SELECT b FROM t2
WHERE EXISTS (
SELECT t3.c
FROM t4
LEFT JOIN t3 ON t3.c != 0
)
);

explain:

expected result:

------

------

------

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=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

bzr version-info
revision-id: <email address hidden>
date: 2011-07-20 11:56:28 +0400
build-date: 2011-07-20 15:58:31 +0300
revno: 3123
branch-nick: maria-5.3