Fixed bug #28375: a query with an NOT IN subquery predicate may cause

a crash when the left operand of the predicate is evaluated to NULL.
It happens when the rows from the inner tables (tables from the subquery)
are accessed by index methods with key values obtained by evaluation of
the left operand of the subquery predicate. When this predicate is
evaluated to NULL an alternative access with full table scan is used
to check whether the result set returned by the subquery is empty or not.
The crash was due to the fact the info about the access methods used for
regular key values was not properly restored after a switch back from the
full scan access method had occurred.
The patch restores this info properly.
The same problem existed for queries with IN subquery predicates if they
were used not at the top level of the queries.

mysql-test/r/subselect3.result

@@ -711,3 +711,34 @@ a
 1
 4
 DROP TABLE t1,t2;
+CREATE TABLE t1 (id int);
+CREATE TABLE t2 (id int PRIMARY KEY);
+CREATE TABLE t3 (id int PRIMARY KEY, name varchar(10));
+INSERT INTO t1 VALUES (2), (NULL), (3), (1);
+INSERT INTO t2 VALUES (234), (345), (457);
+INSERT INTO t3 VALUES (222,'bbb'), (333,'ccc'), (111,'aaa');
+EXPLAIN
+SELECT * FROM t1
+WHERE t1.id NOT IN (SELECT t2.id FROM t2,t3 
+WHERE t3.name='xxx' AND t2.id=t3.id);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where
+2	DEPENDENT SUBQUERY	t2	eq_ref	PRIMARY	PRIMARY	4	func	1	Using where; Using index; Full scan on NULL key
+2	DEPENDENT SUBQUERY	t3	eq_ref	PRIMARY	PRIMARY	4	func	1	Using where; Full scan on NULL key
+SELECT * FROM t1
+WHERE t1.id NOT IN (SELECT t2.id FROM t2,t3 
+WHERE t3.name='xxx' AND t2.id=t3.id);
+id
+2
+NULL
+3
+1
+SELECT (t1.id IN (SELECT t2.id FROM t2,t3 
+WHERE t3.name='xxx' AND t2.id=t3.id)) AS x
+FROM t1;
+x
+0
+0
+0
+0
+DROP TABLE t1,t2,t3;

mysql-test/t/subselect3.test

@@ -546,3 +546,28 @@ SELECT a FROM t1, t2 WHERE a=b AND (b NOT IN (SELECT a FROM t1));
 SELECT a FROM t1, t2 WHERE a=b AND (b NOT IN (SELECT a FROM t1 WHERE a > 4));
 
 DROP TABLE t1,t2;
+
+#
+# Bug #28375: crash for NOT IN subquery predicate when left operand becomes NULL  
+#
+
+CREATE TABLE t1 (id int);
+CREATE TABLE t2 (id int PRIMARY KEY);
+CREATE TABLE t3 (id int PRIMARY KEY, name varchar(10));
+INSERT INTO t1 VALUES (2), (NULL), (3), (1);
+INSERT INTO t2 VALUES (234), (345), (457);
+INSERT INTO t3 VALUES (222,'bbb'), (333,'ccc'), (111,'aaa');
+
+EXPLAIN
+SELECT * FROM t1
+  WHERE t1.id NOT IN (SELECT t2.id FROM t2,t3 
+                        WHERE t3.name='xxx' AND t2.id=t3.id);
+SELECT * FROM t1
+  WHERE t1.id NOT IN (SELECT t2.id FROM t2,t3 
+                        WHERE t3.name='xxx' AND t2.id=t3.id);
+
+SELECT (t1.id IN (SELECT t2.id FROM t2,t3 
+                    WHERE t3.name='xxx' AND t2.id=t3.id)) AS x
+  FROM t1;
+
+DROP TABLE t1,t2,t3;   

sql/item_subselect.cc

@@ -1829,6 +1829,8 @@ int subselect_single_select_engine::exec()
             if (cond_guard && !*cond_guard)
             {
               /* Change the access method to full table scan */
+              tab->save_read_first_record= tab->read_first_record;
+              tab->save_read_record= tab->read_record.read_record;
               tab->read_first_record= init_read_record_seq;
               tab->read_record.record= tab->table->record[0];
               tab->read_record.thd= join->thd;
@@ -1849,8 +1851,8 @@ int subselect_single_select_engine::exec()
       JOIN_TAB *tab= *ptab;
       tab->read_record.record= 0;
       tab->read_record.ref_length= 0;
-      tab->read_first_record= join_read_always_key_or_null;
-      tab->read_record.read_record= join_read_next_same_or_null;
+      tab->read_first_record= tab->save_read_first_record; 
+      tab->read_record.read_record= tab->save_read_record;
     }
     executed= 1;
     thd->where= save_where;

sql/sql_select.h

@@ -159,6 +159,13 @@ typedef struct st_join_table {
   Read_record_func read_first_record;
   Next_select_func next_select;
   READ_RECORD	read_record;
+  /* 
+    Currently the following two fields are used only for a [NOT] IN subquery
+    if it is executed by an alternative full table scan when the left operand of
+    the subquery predicate is evaluated to NULL.
+  */  
+  Read_record_func save_read_first_record;/* to save read_first_record */ 
+  int (*save_read_record) (READ_RECORD *);/* to save read_record.read_record */
   double	worst_seeks;
   key_map	const_keys;			/* Keys with constant part */
   key_map	checked_keys;			/* Keys checked in find_best */