Fix LP BUG#778413

Analysis:
The subquery is evaluated first during ref-optimization of the outer
query because the subquery is considered constant from the perspective
of the outer query. Thus an attempt is made to evaluate the MAX subquery
and use the new constant to drive an index nested loops join.
During this evaluation the inner-most subquery replaces the JOIN_TAB
with a new one that fetches the data from a temp table.
The function select_describe crashes at the lines:
        TABLE_LIST *real_table= table->pos_in_table_list; 
	item_list.push_back(new Item_string(real_table->alias,
					    strlen(real_table->alias),
					    cs));
because 'table' is a temp table, and it has no corresponding table
reference. This 'real_table' is NULL, and real_table->alias results
in a crash.

Solution:
In the spirit of MWL#89 prevent the evaluation of expensive predicates
during optimization. This patch prevents the evaluation of expensive
predicates during ref optimization.


sql/item_subselect.h:
  Remove unused class member. Not needed for the fix, but noticed now and removed.

mysql-test/r/group_min_max.result

@@ -2412,7 +2412,7 @@ EXPLAIN SELECT 1 FROM t1 AS t1_outer1 JOIN t1 AS t1_outer2
 ON t1_outer1.a = (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) 
 AND t1_outer1.b = t1_outer2.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1_outer1	ref	a	a	5	const	1	Using where; Using index
+1	PRIMARY	t1_outer1	ref	a	a	5	const	1	Using index
 1	PRIMARY	t1_outer2	index	NULL	a	10	NULL	15	Using where; Using index; Using join buffer (flat, BNL join)
 2	SUBQUERY	t1	range	NULL	a	5	NULL	8	Using index for group-by
 EXPLAIN SELECT (SELECT (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) x

mysql-test/r/subselect.result

@@ -370,7 +370,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37		1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where 1) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where 1
+Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -549,7 +549,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1'))
+Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1') and ('3' = 3))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);

mysql-test/r/subselect4.result

@@ -1762,3 +1762,23 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t2.f10);
 f4
 drop table t1,t2,t3;
+#                                                                                                                                                     
+# LP BUG#778413 Third crash in select_describe() in maria-5.3-mwl89
+#                                                                                                                                                     
+CREATE TABLE t1 ( f11 int) ;
+INSERT INTO t1 VALUES (1),(1);
+CREATE TABLE t2 ( f1 int NOT NULL) ;
+INSERT INTO t2 VALUES (20);
+CREATE TABLE t3 (f3 int) ;
+INSERT INTO t3 VALUES (2),(2);
+EXPLAIN SELECT * FROM t2
+WHERE t2.f1 = (
+SELECT MAX( f3 ) FROM t3
+WHERE EXISTS (
+SELECT DISTINCT f11
+FROM t1));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	system	NULL	NULL	NULL	NULL	1	
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	2	
+3	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary
+drop table t1, t2, t3;

mysql-test/r/subselect_no_mat.result

@@ -374,7 +374,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37		1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where 1) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where 1
+Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -553,7 +553,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1'))
+Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1') and ('3' = 3))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);

mysql-test/r/subselect_no_opts.result

@@ -371,7 +371,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37		1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where 1) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where 1
+Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -550,7 +550,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1'))
+Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1') and ('3' = 3))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);

mysql-test/r/subselect_no_semijoin.result

@@ -371,7 +371,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37		1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where 1) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where 1
+Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -550,7 +550,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1'))
+Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1') and ('3' = 3))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);

mysql-test/t/subselect4.test

@@ -1434,3 +1434,26 @@ SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t
 SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t2.f10);
 
 drop table t1,t2,t3;
+
+
+--echo #                                                                                                                                                     
+--echo # LP BUG#778413 Third crash in select_describe() in maria-5.3-mwl89
+--echo #                                                                                                                                                     
+
+CREATE TABLE t1 ( f11 int) ;
+INSERT INTO t1 VALUES (1),(1);
+
+CREATE TABLE t2 ( f1 int NOT NULL) ;
+INSERT INTO t2 VALUES (20);
+
+CREATE TABLE t3 (f3 int) ;
+INSERT INTO t3 VALUES (2),(2);
+
+EXPLAIN SELECT * FROM t2
+WHERE t2.f1 = (
+        SELECT MAX( f3 ) FROM t3
+        WHERE EXISTS (
+                SELECT DISTINCT f11
+                FROM t1));
+
+drop table t1, t2, t3;

sql/item_cmpfunc.cc

@@ -5755,7 +5755,7 @@ void Item_equal::update_const()
   Item *item;
   while ((item= it++))
   {
-    if (item->const_item())
+    if (item->const_item() && !item->is_expensive())
     {
       if (item == equal_items.head())
         with_const= TRUE;

sql/item_subselect.h

@@ -619,7 +619,6 @@ class subselect_engine: public Sql_alloc
 class subselect_single_select_engine: public subselect_engine
 {
   bool prepared; /* simple subselect is prepared */
-  bool optimized; /* simple subselect is optimized */
   bool executed; /* simple subselect is executed */
   st_select_lex *select_lex; /* corresponding select_lex */
   JOIN * join; /* corresponding JOIN structure */

sql/sql_select.cc

@@ -9469,7 +9469,7 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
     Item *orig_field_item= 0;
     if (left_item->type() == Item::FIELD_ITEM &&
         !((Item_field*)left_item)->depended_from &&
-        right_item->const_item())
+        right_item->const_item() && !right_item->is_expensive())
     {
       orig_field_item= left_item;
       field_item= (Item_field *) left_item;
@@ -9477,7 +9477,7 @@ static bool check_simple_equality(Item *left_item, Item *right_item,
     }
     else if (right_item->type() == Item::FIELD_ITEM &&
              !((Item_field*)right_item)->depended_from &&
-             left_item->const_item())
+             left_item->const_item() && !left_item->is_expensive())
     {
       orig_field_item= right_item;
       field_item= (Item_field *) right_item;