Fix LP BUG#777597

Analysis:
During optimization of the subquery, in the call chain:

update_ref_and_keys -> add_key_fields ->
merge_key_fields -> Item_direct_ref::is_null -> Item_cache::is_null

The call to Item_cache::is_null() returns TRUE, which is wrong.
This results in Item_null replacing the field 'f3' in the KEY_FIELD,
then this Item_null is used for index access, producing a wrong result.

The reason why Item_cache::is_null returns wrong result is that
this Item_cache object is a cache of the left operand of IN, and was
updated in Item_in_optimizer::val_int. In MWL#89 the latter method is
called during the execution phase, which is after we optimize the subquery.
Therefore during the optization phase the left operand cache of IN was
not updated.

Solution:
Update the left operand cache during optimization if it is a constant.

This bug fix also discoveres and fixes a wrong IF statement in
convert_constant_item().

mysql-test/r/subselect4.result

@@ -1317,7 +1317,7 @@ EXPLAIN
 SELECT i FROM t1 WHERE (1) NOT IN (SELECT i FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
-2	DEPENDENT SUBQUERY	t2	ref_or_null	k	k	5	const	2	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	k	k	5	const	2	Using index
 DROP TABLE t2;
 DROP TABLE t1;
 #
@@ -1743,3 +1743,22 @@ SELECT f2 FROM t1 WHERE ( f2 ) IN ( SELECT t3.f2 FROM t3 JOIN t2 ON t2.f1 = 1 )
 )
 NULL
 drop table t1, t2, t3;
+#                                                                                                                                                     
+# LP BUG#777597 Wrong result with multipart keys, in_to_exists=on, NOT IN in MWL#89
+#                                                                                                                                                     
+CREATE TABLE t1 ( f4 int);
+INSERT IGNORE INTO t1 VALUES (2),(2);
+CREATE TABLE t2 ( f3 int, f10 int, KEY (f10,f3) );
+INSERT IGNORE INTO t2 VALUES (6, 1), (6, 1);
+CREATE TABLE t3 ( f10 int );
+INSERT IGNORE INTO t3 VALUES (1);
+SET SESSION optimizer_switch='in_to_exists=on,materialization=off';
+EXPLAIN
+SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t2.f10);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
+2	DEPENDENT SUBQUERY	t3	system	NULL	NULL	NULL	NULL	1	
+2	DEPENDENT SUBQUERY	t2	ref_or_null	f10	f10	10	const,const	2	Using where; Using index
+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;

mysql-test/r/subselect_mat.result

@@ -1395,7 +1395,7 @@ SELECT * FROM t2 WHERE (SELECT f3a FROM t3) NOT IN (SELECT f1a FROM t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
 3	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
-2	SUBQUERY	t3	system	NULL	NULL	NULL	NULL	0	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 SELECT * FROM t2 WHERE (SELECT f3a FROM t3) NOT IN (SELECT f1a FROM t1);
 f2
 EXPLAIN
@@ -1403,7 +1403,7 @@ SELECT (SELECT f3a FROM t3) NOT IN (SELECT f1a FROM t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	SUBQUERY	t3	system	NULL	NULL	NULL	NULL	0	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 SELECT (SELECT f3a FROM t3) NOT IN (SELECT f1a FROM t1);
 (SELECT f3a FROM t3) NOT IN (SELECT f1a FROM t1)
 NULL
@@ -1412,7 +1412,7 @@ SELECT * FROM t2 WHERE (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
 3	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
-2	SUBQUERY	t3	system	NULL	NULL	NULL	NULL	0	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 SELECT * FROM t2 WHERE (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1);
 f2
 EXPLAIN
@@ -1420,7 +1420,7 @@ SELECT (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	SUBQUERY	t3	system	NULL	NULL	NULL	NULL	0	const row not found
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 SELECT (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1);
 (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1)
 NULL

mysql-test/t/subselect4.test

@@ -1412,3 +1412,25 @@ SELECT STRAIGHT_JOIN (
 );
 
 drop table t1, t2, t3;
+
+
+--echo #                                                                                                                                                     
+--echo # LP BUG#777597 Wrong result with multipart keys, in_to_exists=on, NOT IN in MWL#89
+--echo #                                                                                                                                                     
+
+CREATE TABLE t1 ( f4 int);
+INSERT IGNORE INTO t1 VALUES (2),(2);
+
+CREATE TABLE t2 ( f3 int, f10 int, KEY (f10,f3) );
+INSERT IGNORE INTO t2 VALUES (6, 1), (6, 1);
+
+CREATE TABLE t3 ( f10 int );
+INSERT IGNORE INTO t3 VALUES (1);
+
+SET SESSION optimizer_switch='in_to_exists=on,materialization=off';
+
+EXPLAIN
+SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t2.f10);
+SELECT * FROM t1 WHERE ( 6 ) NOT IN ( SELECT t2.f3 FROM t2 JOIN t3 ON t3.f10 = t2.f10);
+
+drop table t1,t2,t3;

sql/item_cmpfunc.cc

@@ -421,14 +421,12 @@ static bool convert_constant_item(THD *thd, Item_field *field_item,
     thd->count_cuted_fields= CHECK_FIELD_IGNORE;
 
     /*
-      Store the value of the field/constant if it references an outer field
-      because the call to save_in_field below overrides that value.
-      Don't save field value if no data has been read yet.
-      Outer constant values are always saved.
+      Store the value of the field/constant because the call to save_in_field
+      below overrides that value. Don't save field value if no data has been
+      read yet.
     */
-    bool save_field_value= (field_item->depended_from &&
-                            (field_item->const_item() ||
-                             !(field->table->status & STATUS_NO_RECORD)));
+    bool save_field_value= (field_item->const_item() ||
+                            !(field->table->status & STATUS_NO_RECORD));
     if (save_field_value)
       orig_field_val= field->val_int();
     if (!(*item)->is_null() && !(*item)->save_in_field(field, 1))
@@ -1743,7 +1741,10 @@ bool Item_in_optimizer::fix_left(THD *thd, Item **ref)
   with_sum_func= args[0]->with_sum_func;
   with_field= args[0]->with_field;
   if ((const_item_cache= args[0]->const_item()))
+  {
     cache->store(args[0]);
+    cache->cache_value();
+  }
   return 0;
 }