Fixed LP bug #729039.

If join condition is of the form <t2.key>=<t1.no_key> then the server
performs no index look-ups when looking for matching rows of t2 for
the rows from t1 with t1.no_key=NULL. It happens because the function
add_not_null_conds() injects an additional condition of the form 
IS NOT NULL(<t1.no_key>) into the WHERE condition.
However if the join condition was of the form <t.key>=<outer_ref> no
additional null rejecting predicate was generated. This could lead
to extra records in the result set if the value of <outer_ref> happened
to be NULL.
The new code injects null rejecting predicates of the form 
IS NOT NULL(<outer_ref>) and evaluates them before the first row
the subquery is constructed.

mysql-test/r/subselect.result

@@ -5018,3 +5018,31 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	SUBQUERY	it2	ALL	NULL	NULL	NULL	NULL	4	
 2	SUBQUERY	it3	ALL	NULL	NULL	NULL	NULL	6	Using join buffer (flat, BNL join)
 DROP TABLE IF EXISTS ot1, ot4, it2, it3;
+#
+# Bug#729039: NULL keys used to evaluate subquery
+#
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (NULL), (1), (NULL), (2);
+CREATE TABLE t2 (a int, INDEX idx(a)) ;
+INSERT INTO t2 VALUES (NULL), (1), (NULL);
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX () WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX() WHERE t2.a = t1.a);
+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	ALL	NULL	NULL	NULL	NULL	3	Using where
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+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	ref	idx	idx	5	test.t1.a	2	Using index
+DROP TABLE t1,t2;

mysql-test/r/subselect_no_mat.result

@@ -5020,6 +5020,34 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	it3	ALL	NULL	NULL	NULL	NULL	6	Using join buffer (flat, BNL join)
 1	PRIMARY	ot4	ALL	NULL	NULL	NULL	NULL	8	Using where; End temporary; Using join buffer (flat, BNL join)
 DROP TABLE IF EXISTS ot1, ot4, it2, it3;
+#
+# Bug#729039: NULL keys used to evaluate subquery
+#
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (NULL), (1), (NULL), (2);
+CREATE TABLE t2 (a int, INDEX idx(a)) ;
+INSERT INTO t2 VALUES (NULL), (1), (NULL);
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX () WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX() WHERE t2.a = t1.a);
+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	ALL	NULL	NULL	NULL	NULL	3	Using where
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+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	ref	idx	idx	5	test.t1.a	2	Using index
+DROP TABLE t1,t2;
 set optimizer_switch=default;
 select @@optimizer_switch like '%materialization=on%';
 @@optimizer_switch like '%materialization=on%'

mysql-test/r/subselect_no_opts.result

@@ -5017,4 +5017,32 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	DEPENDENT SUBQUERY	it2	ALL	NULL	NULL	NULL	NULL	4	Using where
 2	DEPENDENT SUBQUERY	it3	ALL	NULL	NULL	NULL	NULL	6	Using where; Using join buffer (flat, BNL join)
 DROP TABLE IF EXISTS ot1, ot4, it2, it3;
+#
+# Bug#729039: NULL keys used to evaluate subquery
+#
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (NULL), (1), (NULL), (2);
+CREATE TABLE t2 (a int, INDEX idx(a)) ;
+INSERT INTO t2 VALUES (NULL), (1), (NULL);
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX () WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX() WHERE t2.a = t1.a);
+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	ALL	NULL	NULL	NULL	NULL	3	Using where
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+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	ref	idx	idx	5	test.t1.a	2	Using index
+DROP TABLE t1,t2;
 set optimizer_switch=default;

mysql-test/r/subselect_no_semijoin.result

@@ -5017,4 +5017,32 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	SUBQUERY	it2	ALL	NULL	NULL	NULL	NULL	4	
 2	SUBQUERY	it3	ALL	NULL	NULL	NULL	NULL	6	Using join buffer (flat, BNL join)
 DROP TABLE IF EXISTS ot1, ot4, it2, it3;
+#
+# Bug#729039: NULL keys used to evaluate subquery
+#
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (NULL), (1), (NULL), (2);
+CREATE TABLE t2 (a int, INDEX idx(a)) ;
+INSERT INTO t2 VALUES (NULL), (1), (NULL);
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX () WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 USE INDEX() WHERE t2.a = t1.a);
+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	ALL	NULL	NULL	NULL	NULL	3	Using where
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+a
+1
+EXPLAIN
+SELECT * FROM t1
+WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+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	ref	idx	idx	5	test.t1.a	2	Using index
+DROP TABLE t1,t2;
 set optimizer_switch=default;

mysql-test/t/subselect.test

@@ -4293,3 +4293,26 @@ eval explain $query;
 DROP TABLE IF EXISTS ot1, ot4, it2, it3;
 
 
+--echo #
+--echo # Bug#729039: NULL keys used to evaluate subquery
+--echo #
+
+CREATE TABLE t1 (a int) ;
+INSERT INTO t1 VALUES (NULL), (1), (NULL), (2);
+
+CREATE TABLE t2 (a int, INDEX idx(a)) ;
+INSERT INTO t2 VALUES (NULL), (1), (NULL);
+
+SELECT * FROM t1
+  WHERE EXISTS (SELECT a FROM t2 USE INDEX () WHERE t2.a = t1.a);
+EXPLAIN
+SELECT * FROM t1
+  WHERE EXISTS (SELECT a FROM t2 USE INDEX() WHERE t2.a = t1.a);
+
+SELECT * FROM t1
+  WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+EXPLAIN
+SELECT * FROM t1
+  WHERE EXISTS (SELECT a FROM t2 WHERE t2.a = t1.a);
+
+DROP TABLE t1,t2;

sql/sql_select.cc

@@ -6891,7 +6891,7 @@ static void add_not_null_conds(JOIN *join)
             UPDATE t1 SET t1.f2=(SELECT MAX(t2.f4) FROM t2 WHERE t2.f3=t1.f1);
             not_null_item is the t1.f1, but it's referred_tab is 0.
           */
-          if (!referred_tab || referred_tab->join != join)
+          if (!referred_tab)
             continue;
           if (!(notnull= new Item_func_isnotnull(not_null_item)))
             DBUG_VOID_RETURN;
@@ -6908,9 +6908,14 @@ static void add_not_null_conds(JOIN *join)
                                            QT_ORDINARY););
           if (!tab->first_inner)
 	  {
-            COND *new_cond= referred_tab->select_cond;
+            COND *new_cond= referred_tab->join == join ? 
+                              referred_tab->select_cond :
+                              join->outer_ref_cond;
             add_cond_and_fix(&new_cond, notnull);
-            referred_tab->set_select_cond(new_cond, __LINE__);
+            if (referred_tab->join == join)
+              referred_tab->set_select_cond(new_cond, __LINE__);
+            else 
+              join->outer_ref_cond= new_cond;
           }
           else
             add_cond_and_fix(tab->first_inner->on_expr_ref, notnull);
@@ -7127,6 +7132,15 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	  DBUG_PRINT("info",("Found impossible WHERE condition"));
 	  DBUG_RETURN(1);	 // Impossible const condition
         }
+
+        COND *outer_ref_cond= make_cond_for_table(cond, 
+                                                  OUTER_REF_TABLE_BIT,
+                                                  (table_map) 0, FALSE, FALSE);
+        if (outer_ref_cond)
+	{
+          add_cond_and_fix(&outer_ref_cond, join->outer_ref_cond);
+          join->outer_ref_cond= outer_ref_cond;
+        }
       }
     }
 
@@ -13393,7 +13407,10 @@ do_select(JOIN *join,List<Item> *fields,TABLE *table,Procedure *procedure)
   else
   {
     DBUG_ASSERT(join->tables);
-    error= join->first_select(join,join_tab,0);
+    if (join->outer_ref_cond && !join->outer_ref_cond->val_int())
+      error= NESTED_LOOP_NO_MORE_ROWS;
+    else
+      error= join->first_select(join,join_tab,0);
     if (error == NESTED_LOOP_OK || error == NESTED_LOOP_NO_MORE_ROWS)
       error= join->first_select(join,join_tab,1);
     if (error == NESTED_LOOP_QUERY_LIMIT)

sql/sql_select.h

@@ -798,6 +798,7 @@ class JOIN :public Sql_alloc
   ORDER *order, *group_list, *proc_param; //hold parameters of mysql_select
   COND *conds;                            // ---"---
   Item *conds_history;                    // store WHERE for explain
+  COND *outer_ref_cond;       ///<part of conds containing only outer references
   TABLE_LIST *tables_list;           ///<hold 'tables' parameter of mysql_select
   List<TABLE_LIST> *join_list;       ///< list of joined tables in reverse order
   COND_EQUAL *cond_equal;
@@ -903,6 +904,7 @@ class JOIN :public Sql_alloc
 
     no_const_tables= FALSE;
     first_select= sub_select;
+    outer_ref_cond= 0;
   }
 
   int prepare(Item ***rref_pointer_array, TABLE_LIST *tables, uint wind_num,