Wrong result with DISTINCT + multipart keys after WL#106

[Philip Stoev]

Not repeatable before WL#106. Not repeatable with mysql-5.5 . Not repeatable without views. Not influenced by any optimizer switches.

Even after the fix for 806097 the following query:

SELECT DISTINCT t1.b FROM t2 JOIN ( t1 JOIN t3 ON t3.a = t1.d) ;

does not return all rows if executed with a derived table or a view.

explain:

| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 2 | |
| 2 | DERIVED | t2 | system | NULL | NULL | NULL | NULL | 1 | Using temporary |
| 2 | DERIVED | t3 | ALL | NULL | NULL | NULL | NULL | 2 | Using where; Distinct |
| 2 | DERIVED | t1 | ref | d | d | 5 | bug.t3.a | 1 | Using where; Distinct |

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=on,derived_with_keys=on,firstmatch=off,loosescan=off,materialization=on,in_to_exists=on,semijoin=off,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=on,table_elimination=on

bzr version-info:

revision-id: <email address hidden>
date: 2011-07-11 10:56:48 -0700
build-date: 2011-07-12 12:09:03 +0300
revno: 3100
branch-nick: maria-5.3

test case:

CREATE TABLE t1 ( b int , c int, d int , KEY (d,c) ) ;
INSERT INTO t1 VALUES (28,0,'j'),(29,8,'c');

CREATE TABLE t2 ( a int) ;
INSERT INTO t2 VALUES (0);

CREATE TABLE t3 ( a varchar(32)) ;
INSERT INTO t3 VALUES ('j'),('c');

SELECT * FROM ( SELECT DISTINCT t1.b FROM t2 JOIN ( t1 JOIN t3 ON t3.a = t1.d) ) AS a1;

[Philip Stoev (pstoev-askmonty)]

Here is another example without multipart keys, requires join_cache_level=0:

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

DROP TABLE IF EXISTS t2;
CREATE TABLE t2 (a int) ;
INSERT INTO t2 VALUES (NULL),(NULL),(NULL),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0);

SET SESSION join_cache_level=0;

SELECT DISTINCT t2.a FROM t1 , t2;
SELECT * FROM ( SELECT DISTINCT t2.a FROM t1 , t2 ) AS alias1 ;