Backport into build-201006221614-5.1.46sp1

> ------------------------------------------------------------
> revno: 3351.41.1
> revision-id: alexey.kopytov@sun.com-20100430111048-jdls6ofn4kkmpt09
> parent: sergey.glukhov@sun.com-20100329134249-03wyhzp5k92dzhcb
> committer: Alexey Kopytov <Alexey.Kopytov@Sun.com>
> branch nick: my51-bug48419
> timestamp: Fri 2010-04-30 15:10:48 +0400
> message:
>   Bug #48419: another explain crash..
>   
>   WHERE predicates containing references to empty tables in a
>   subquery were handled incorrectly by the optimizer when
>   executing EXPLAIN. As a result, the optimizer could try to
>   evaluate such predicates rather than just stop with
>   "Impossible WHERE noticed after reading const tables" as 
>   it would do in a non-subquery case. This led to valgrind 
>   errors and crashes.
>   
>   Fixed the code checking the above condition so that subqueries
>   are not excluded and hence are handled in the same way as top
>   level SELECTs.

mysql-test/r/explain.result

@@ -226,4 +226,16 @@ Warnings:
 Note	1276	Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
 Note	1003	select (select 1 from `test`.`t2` where (`test`.`t2`.`d` = NULL)) AS `(SELECT 1 FROM t2 WHERE d = c)` from `test`.`t1`
 DROP TABLE t1, t2;
+#
+# Bug #48419: another explain crash..
+#
+CREATE TABLE t1 (a INT);
+CREATE TABLE t2 (b BLOB, KEY b(b(100)));
+INSERT INTO t2 VALUES ('1'), ('2'), ('3');
+FLUSH TABLES;
+EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT 1 FROM t1 t JOIN t2 WHERE b <= 1 AND t.a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+DROP TABLE t1, t2;
 End of 5.1 tests.

mysql-test/r/ps.result

@@ -155,24 +155,24 @@ execute stmt1 ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 6	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
-5	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
-4	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
+5	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+4	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 execute stmt1 ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 6	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
-5	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
-4	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
+5	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+4	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 explain SELECT (SELECT SUM(c1 + c12 + 0.0) FROM t2 where (t1.c2 - 0e-3) = t2.c2 GROUP BY t1.c15 LIMIT 1) as scalar_s, exists (select 1.0e+0 from t2 where t2.c3 * 9.0000000000 = t1.c4) as exists_s, c5 * 4 in (select c6 + 0.3e+1 from t2) as in_s, (c7 - 4, c8 - 4) in (select c9 + 4.0, c10 + 40e-1 from t2) as in_row_s FROM t1, (select c25 x, c32 y from t2) tt WHERE x * 1 = c25;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 6	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
-5	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
-4	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
+5	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+4	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 deallocate prepare stmt1;

mysql-test/t/explain.test

@@ -198,4 +198,19 @@ INSERT INTO t2 VALUES (NULL), (0);
 EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;
 DROP TABLE t1, t2;
 
+
+--echo #
+--echo # Bug #48419: another explain crash..
+--echo #
+
+CREATE TABLE t1 (a INT);
+CREATE TABLE t2 (b BLOB, KEY b(b(100)));
+INSERT INTO t2 VALUES ('1'), ('2'), ('3');
+
+FLUSH TABLES;
+
+EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT 1 FROM t1 t JOIN t2 WHERE b <= 1 AND t.a);
+
+DROP TABLE t1, t2;
+
 --echo End of 5.1 tests.

sql/sql_select.cc

@@ -1107,8 +1107,7 @@ JOIN::optimize()
   }
 
   if (conds && const_table_map != found_const_table_map &&
-      (select_options & SELECT_DESCRIBE) &&
-      select_lex->master_unit() == &thd->lex->unit) // upper level SELECT
+      (select_options & SELECT_DESCRIBE))
   {
     conds=new Item_int((longlong) 0,1);	// Always false
   }