Fixed the bug mdev-12673.

This patch corrects the fix for the bug mdev-10693.
It is critical for the function get_best_combination() not to call
create_ref_for_key() for constant tables.
This bug could manifest itself only in multi-table subqueries where
one of the tables is accessed by a constant primary key.

mysql-test/r/subselect_mat_cost_bugs.result

@@ -400,3 +400,45 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
 c1	c2
 drop table t1, t2;
+#
+# MDEV-12673: cost-based choice between materialization and in-to-exists
+#
+CREATE TABLE t1 (
+pk1 int, a1 varchar(3), b1 varchar(3), PRIMARY KEY (pk1), KEY(a1), KEY(b1)
+) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,'foo','bar'),(2,'bar','foo');
+CREATE TABLE t2 (pk2 INT PRIMARY KEY, a2 VARCHAR(3), KEY(a2)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,'abc'),(2,'xyz'),(3,'foo');
+SELECT 'qux' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+'qux' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 )
+0
+SELECT 'bar' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+'bar' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 )
+1
+EXPLAIN 
+SELECT 'bar' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+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
+2	SUBQUERY	t2	const	PRIMARY,a2	PRIMARY	4	const	1	
+2	SUBQUERY	t1	ref	a1,b1	b1	6	const	1	Using where
+DROP TABLE t1,t2;
+CREATE TABLE t1 (i1 INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1);
+CREATE TABLE t2 (i2 int, c2 varchar(3), KEY(i2,c2)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,'abc'),(2,'foo');
+CREATE TABLE t3 (pk3 int PRIMARY KEY, c3 varchar(3)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (1,'foo'),(2,'bar');
+SELECT * FROM t1 WHERE i1 NOT IN ( 
+SELECT i2 FROM t2 RIGHT JOIN t3 ON (c3 = c2) WHERE pk3 = i1 
+);
+i1
+1
+EXPLAIN
+SELECT * FROM t1 WHERE i1 NOT IN ( 
+SELECT i2 FROM t2 RIGHT JOIN t3 ON (c3 = c2) WHERE pk3 = i1 
+);
+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	t3	const	PRIMARY	PRIMARY	4	const	1	
+2	DEPENDENT SUBQUERY	t2	index	NULL	i2	11	NULL	2	Using where; Using index
+DROP TABLE t1,t2,t3;

mysql-test/t/subselect_mat_cost_bugs.test

@@ -424,3 +424,42 @@ explain select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
 select * from t1 where c1 = 'a2' and (c1, c2) not in (select * from t2);
 
 drop table t1, t2;
+
+--echo #
+--echo # MDEV-12673: cost-based choice between materialization and in-to-exists
+--echo #
+
+CREATE TABLE t1 (
+ pk1 int, a1 varchar(3), b1 varchar(3), PRIMARY KEY (pk1), KEY(a1), KEY(b1)
+) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,'foo','bar'),(2,'bar','foo');
+
+CREATE TABLE t2 (pk2 INT PRIMARY KEY, a2 VARCHAR(3), KEY(a2)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,'abc'),(2,'xyz'),(3,'foo');
+
+SELECT 'qux' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+SELECT 'bar' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+EXPLAIN 
+SELECT 'bar' IN ( SELECT a1 FROM t1 INNER JOIN t2 WHERE a2 = b1 AND pk2 = 3 );
+
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (i1 INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1);
+
+CREATE TABLE t2 (i2 int, c2 varchar(3), KEY(i2,c2)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1,'abc'),(2,'foo');
+
+CREATE TABLE t3 (pk3 int PRIMARY KEY, c3 varchar(3)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (1,'foo'),(2,'bar');
+
+SELECT * FROM t1 WHERE i1 NOT IN ( 
+  SELECT i2 FROM t2 RIGHT JOIN t3 ON (c3 = c2) WHERE pk3 = i1 
+);
+
+EXPLAIN
+SELECT * FROM t1 WHERE i1 NOT IN ( 
+  SELECT i2 FROM t2 RIGHT JOIN t3 ON (c3 = c2) WHERE pk3 = i1 
+);
+
+DROP TABLE t1,t2,t3;

sql/sql_select.cc

@@ -7844,12 +7844,14 @@ get_best_combination(JOIN *join)
   {
     if (j->bush_children)
       j= j->bush_children->start;
-      
+    
     used_tables|= j->table->map;
-    if ((keyuse= join->best_positions[tablenr].key) &&
-        create_ref_for_key(join, j, keyuse, TRUE, used_tables))
-     DBUG_RETURN(TRUE);              // Something went wrong
-
+    if (j->type != JT_CONST && j->type != JT_SYSTEM)
+    {
+      if ((keyuse= join->best_positions[tablenr].key) &&
+          create_ref_for_key(join, j, keyuse, TRUE, used_tables))
+        DBUG_RETURN(TRUE);              // Something went wrong
+    }
     if (j->last_leaf_in_bush)
       j= j->bush_root_tab;
   }