database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-08-08 11:22:35 +03:00
Code Activity

Fixed bug lp:800679

Browse Source 
Analysis:
  The failed assert ensured that the choice of subquery strategy
  is performed only for queries with at least one table. If there
  is a LIMIT 0 clause all tables are removed, and the subquery is
  neither optimized, nor executed during actual optimization. However,
  if the query is EXPLAIN-ed, the EXPLAIN execution path doesn't remove
  the query tables if there is a LIMIT 0 clause. As a result, the
  subquery optimization code is called, which violates the ASSERT
  condition.
  
Solution:
  Transform the assert into a condition, and if the outer query
  has no tables assume that there will be at most one subquery
  execution.
  
  There is potentially a better solution by reengineering the
  EXPLAIN/optimize code, so that subquery optimization is not
  done if not needed. Such a solution would be a lot bigger and
  more complex than a bug fix.
This commit is contained in:
unknown
2011-06-28 15:48:44 +03:00
parent 95cba1043e
commit 78fa331eaa
3 changed files with 45 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
mysql-test/r/subselect_mat_cost_bugs.result
View File

@@ -295,3 +295,24 @@ id select_type table type possible_keys key key_len ref rows Extra
select c1 from t1 where c1 in (select kp1 from t2 where kp2 = 10 and c2 = 4) or c1 > 7;
c1
drop table t1, t2;
#
# LP BUG#800679: Assertion `outer_join->table_count > 0' failed in
# JOIN::choose_subquery_plan() with materialization=on,semijoin=off
#
CREATE TABLE t1 ( f1 int);
insert into t1 values (1),(2);
CREATE TABLE t2 ( f1 int);
insert into t2 values (1),(2);
SET @@optimizer_switch='materialization=on,semijoin=off';
EXPLAIN
SELECT * FROM t1
WHERE (f1) IN (SELECT f1 FROM t2)
LIMIT 0;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
SELECT * FROM t1
WHERE (f1) IN (SELECT f1 FROM t2)
LIMIT 0;
f1
drop table t1, t2;

23
mysql-test/t/subselect_mat_cost_bugs.test
View File

@@ -326,3 +326,26 @@ select c1 from t1 where c1 in (select kp1 from t2 where kp2 = 10 and c2 = 4) or
select c1 from t1 where c1 in (select kp1 from t2 where kp2 = 10 and c2 = 4) or c1 > 7;
drop table t1, t2;
--echo #
--echo # LP BUG#800679: Assertion `outer_join->table_count > 0' failed in
--echo # JOIN::choose_subquery_plan() with materialization=on,semijoin=off
--echo #
CREATE TABLE t1 ( f1 int);
insert into t1 values (1),(2);
CREATE TABLE t2 ( f1 int);
insert into t2 values (1),(2);
SET @@optimizer_switch='materialization=on,semijoin=off';
EXPLAIN
SELECT * FROM t1
WHERE (f1) IN (SELECT f1 FROM t2)
LIMIT 0;
SELECT * FROM t1
WHERE (f1) IN (SELECT f1 FROM t2)
LIMIT 0;
drop table t1, t2;

3
sql/opt_subselect.cc
View File

@@ -4360,7 +4360,7 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
by the IN predicate.
*/
outer_join= unit->outer_select() ? unit->outer_select()->join : NULL;
if (outer_join)
if (outer_join && outer_join->table_count > 0)
{
/*
The index of the last JOIN_TAB in the outer JOIN where in_subs is
@@ -4373,7 +4373,6 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
JOIN_TAB, and their join_tab_idx remains MAX_TABLES. Such predicates
are evaluated for each complete row of the outer join.
*/
DBUG_ASSERT(outer_join->table_count > 0);
max_outer_join_tab_idx= (in_subs->get_join_tab_idx() == MAX_TABLES) ?
outer_join->table_count - 1:
in_subs->get_join_tab_idx();