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Fix bug lp:858038

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Analysis:
The cause of the bug was the changed meaning of
subselect_partial_match_engine::has_covering_null_row.
Previously it meant that there is row with NULLs in
all nullable fields of the materialized subquery table.
Later it was changed to mean a row with NULLs in all
fields of this table.

At the same time there was a shortcut in
subselect_rowid_merge_engine::partial_match() that
detected a special case where:
- there is no match in any of the columns with NULLs, and
- there is no NULL-only row that covers all columns with
  NULLs.
With the change in the meaning of has_covering_null_row,
the condition that detected this special case was incomplete.
This resulted in an incorrect FALSE, when the result was a
partial match.

Solution:
Expand the condition that detected the special case with the
correct test for the existence of a row with NULL values in
all columns that contain NULLs (a kind of parially covering
NULL-row).
This commit is contained in:
unknown 2011-10-03 22:48:15 +03:00
commit ada0850c04
3 changed files with 58 additions and 1 deletions
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23
mysql-test/t/subselect_mat_cost_bugs.test
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@ -385,3 +385,26 @@ WHERE t3.b > ALL (
set @@optimizer_switch='default';
drop table t3, t4, t5;
--echo #
--echo # LP BUG#858038 The result of a query with NOT IN subquery depends on the state of the optimizer switch
--echo #
create table t1 (c1 char(2) not null, c2 char(2));
create table t2 (c3 char(2), c4 char(2));
insert into t1 values ('a1', 'b1');
insert into t1 values ('a2', 'b2');
insert into t2 values ('x1', 'y1');
insert into t2 values ('a2', null);
set @@optimizer_switch='in_to_exists=off,materialization=on,partial_match_rowid_merge=off,partial_match_table_scan=on';
explain select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
set @@optimizer_switch='in_to_exists=off,materialization=on,partial_match_rowid_merge=on,partial_match_table_scan=off';
explain select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
drop table t1, t2;