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Fix bug lp:809266

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Analysis:
This is a bug in MWL#68, where it was incorrectly assumed
that if there is a match in the only non-null key, then
if there is a covering NULL row on all remaining NULL-able
columns there is a partial match. However, this is not the case,
because even if there is such a null-only sub-row, it is not
guaranteed to be part of the matched sub-row. The matched sub-row
and the NULL-only sub-row may be parts of different rows.

In fact there are two cases:
- there is a complete row with only NULL values, and
- all nullable columns contain only NULL values.

These two cases were incorrectly mixed up in the class member
  subselect_partial_match_engine::covering_null_row_width.


Solution:
The solution is to:
- split covering_null_row_width into two members:
  has_covering_null_row, and has_covering_null_columns, and
- take into account each state during initialization and
  execution.
This commit is contained in:
unknown 2011-07-14 00:15:07 +03:00
commit 1e6bd6b4df
4 changed files with 153 additions and 53 deletions
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46
mysql-test/r/subselect_partial_match.result
View file

@ -99,4 +99,50 @@ FROM t3 LEFT JOIN t2 ON t3.a = t2.a);
d
r
drop table t1, t2, t3;
#
# LP BUG#809266 Diverging results with partial_match_rowid_merge=on
#
CREATE TABLE t1 (c int) ;
INSERT INTO t1 VALUES (0),(0);
CREATE TABLE t2 (a int, b int) ;
INSERT INTO t2 VALUES (6,3), (9,NULL);
set @@optimizer_switch='materialization=on,partial_match_rowid_merge=on,partial_match_table_scan=off,in_to_exists=off';
EXPLAIN
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT b, a FROM t2);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT b, a FROM t2);
c
0
0
EXPLAIN
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT a, b FROM t2);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT a, b FROM t2);
c
0
0
set @@optimizer_switch='materialization=off,in_to_exists=on';
EXPLAIN
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT b, a FROM t2);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2
2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT b, a FROM t2);
c
0
0
EXPLAIN
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT a, b FROM t2);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2
2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
SELECT * FROM t1 WHERE (6, 4 ) NOT IN (SELECT a, b FROM t2);
c
0
0
drop table t1, t2;
set @@optimizer_switch=@save_optimizer_switch;