BUG#20420: optimizer reports wrong keys on left join with IN

 The optimizer needs to evaluate whether predicates are better
 evaluated using an index. IN is one such predicate.
 To qualify an IN predicate must involve a field of the index
 on the left and constant arguments on the right.
 However whether an expression is a constant can be determined only
 by knowing the preceding tables in the join order. 
 Assuming that only IN predicates with expressions on the right that
 are constant for the whole query qualify limits the scope of 
 possible optimizations of the IN predicate (more specifically it
 doesn't allow the "Range checked for each record" optimization for
 such an IN predicate.
 Fixed by not pre-determining the optimizability of the IN predicate
 in the case when all right IN operands are not SQL constant expressions

mysql-test/r/func_in.result

@@ -351,4 +351,47 @@ some_id
 1
 2
 drop table t1;
+CREATE TABLE t1 (a int, b int, PRIMARY KEY (a));
+INSERT INTO t1 VALUES (1,1),(2,1),(3,1),(4,1),(5,1),(6,1);
+CREATE TABLE t2 (a int, b int, PRIMARY KEY (a));
+INSERT INTO t2 VALUES (3,2),(4,2);
+CREATE TABLE t3 (a int PRIMARY KEY);
+INSERT INTO t3 VALUES (1),(2),(3),(4);
+CREATE TABLE t4 (a int PRIMARY KEY);
+INSERT INTO t4 VALUES (1),(2);
+EXPLAIN SELECT STRAIGHT_JOIN * FROM t3 
+JOIN t1 ON t3.a=t1.a 
+JOIN t2 ON t3.a=t2.a
+JOIN t4 WHERE t4.a IN (t1.b, t2.b);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	index	PRIMARY	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	eq_ref	PRIMARY	PRIMARY	4	test.t3.a	1	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t3.a	1	
+1	SIMPLE	t4	ALL	PRIMARY	NULL	NULL	NULL	2	Range checked for each record (index map: 0x1)
+SELECT STRAIGHT_JOIN * FROM t3 
+JOIN t1 ON t3.a=t1.a 
+JOIN t2 ON t3.a=t2.a
+JOIN t4 WHERE t4.a IN (t1.b, t2.b);
+a	a	b	a	b	a
+3	3	1	3	2	1
+3	3	1	3	2	2
+4	4	1	4	2	1
+4	4	1	4	2	2
+EXPLAIN SELECT STRAIGHT_JOIN 
+(SELECT SUM(t4.a) FROM t4 WHERE t4.a IN (t1.b, t2.b)) 
+FROM t3, t1, t2
+WHERE t3.a=t1.a AND t3.a=t2.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t3	index	PRIMARY	PRIMARY	4	NULL	4	Using index
+1	PRIMARY	t1	eq_ref	PRIMARY	PRIMARY	4	test.t3.a	1	
+1	PRIMARY	t2	eq_ref	PRIMARY	PRIMARY	4	test.t3.a	1	
+2	DEPENDENT SUBQUERY	t4	index	NULL	PRIMARY	4	NULL	2	Using where; Using index
+SELECT STRAIGHT_JOIN 
+(SELECT SUM(t4.a) FROM t4 WHERE t4.a IN (t1.b, t2.b)) 
+FROM t3, t1, t2
+WHERE t3.a=t1.a AND t3.a=t2.a;
+(SELECT SUM(t4.a) FROM t4 WHERE t4.a IN (t1.b, t2.b))
+3
+3
+DROP TABLE t1,t2,t3,t4;
 End of 5.0 tests

mysql-test/t/func_in.test

@@ -254,5 +254,41 @@ select some_id from t1 where some_id not in(-4,-1,-4);
 select some_id from t1 where some_id not in(-4,-1,3423534,2342342);
 drop table t1;
 
+#
+# BUG#20420: optimizer reports wrong keys on left join with IN
+#
+CREATE TABLE t1 (a int, b int, PRIMARY KEY (a));
+INSERT INTO t1 VALUES (1,1),(2,1),(3,1),(4,1),(5,1),(6,1);
+
+CREATE TABLE t2 (a int, b int, PRIMARY KEY (a));
+INSERT INTO t2 VALUES (3,2),(4,2);
+
+CREATE TABLE t3 (a int PRIMARY KEY);
+INSERT INTO t3 VALUES (1),(2),(3),(4);
+
+CREATE TABLE t4 (a int PRIMARY KEY);
+INSERT INTO t4 VALUES (1),(2);
+
+EXPLAIN SELECT STRAIGHT_JOIN * FROM t3 
+  JOIN t1 ON t3.a=t1.a 
+  JOIN t2 ON t3.a=t2.a
+  JOIN t4 WHERE t4.a IN (t1.b, t2.b);
+
+SELECT STRAIGHT_JOIN * FROM t3 
+  JOIN t1 ON t3.a=t1.a 
+  JOIN t2 ON t3.a=t2.a
+  JOIN t4 WHERE t4.a IN (t1.b, t2.b);
+
+EXPLAIN SELECT STRAIGHT_JOIN 
+   (SELECT SUM(t4.a) FROM t4 WHERE t4.a IN (t1.b, t2.b)) 
+  FROM t3, t1, t2
+  WHERE t3.a=t1.a AND t3.a=t2.a;
+
+SELECT STRAIGHT_JOIN 
+   (SELECT SUM(t4.a) FROM t4 WHERE t4.a IN (t1.b, t2.b)) 
+  FROM t3, t1, t2
+  WHERE t3.a=t1.a AND t3.a=t2.a;
+
+DROP TABLE t1,t2,t3,t4;  
 
 --echo End of 5.0 tests

sql/item_cmpfunc.h

@@ -965,6 +965,10 @@ class Item_func_in :public Item_func_opt_neg
 {
 public:
   Item_result cmp_type;
+  /* 
+    an array of values when the right hand arguments of IN
+    are all SQL constant and there are no nulls 
+  */
   in_vector *array;
   cmp_item *in_item;
   bool have_null;
@@ -990,7 +994,7 @@ public:
     DBUG_VOID_RETURN;
   }
   optimize_type select_optimize() const
-    { return array ? OPTIMIZE_KEY : OPTIMIZE_NONE; }
+    { return OPTIMIZE_KEY; }
   void print(String *str);
   enum Functype functype() const { return IN_FUNC; }
   const char *func_name() const { return " IN "; }