Manually merged

mysql-test/t/func_in.test:
  Auto merged

mysql-test/r/func_in.result

@@ -202,6 +202,27 @@ select count(*) from t1 where id not in (1,2);
 count(*)
 1
 drop table t1;
+create table t1 (f1 char(1), f2 int);
+insert into t1 values (1,0),('a',1),('z',2);
+select f1 from t1 where f1 in (1,'z');
+f1
+1
+z
+select f2 from t1 where f2 in (1,'z');
+f2
+0
+1
+select f1 from t1 where 'z' in (1,f1);
+f1
+z
+select * from t1 where 'z' in (f2,f1);
+f1	f2
+z	2
+select * from t1 where 1 in (f2,f1);
+f1	f2
+1	0
+a	1
+drop table t1;
 CREATE TABLE t1 (a int PRIMARY KEY);
 INSERT INTO t1 VALUES (44), (45), (46);
 SELECT * FROM t1 WHERE a IN (45);

mysql-test/t/func_in.test

@@ -109,6 +109,18 @@ select count(*) from t1 where id not in (1);
 select count(*) from t1 where id not in (1,2);
 drop table t1;
 
+#
+# Bug#18360 Incorrect type coercion in IN() results in false comparison
+#
+create table t1 (f1 char(1), f2 int);
+insert into t1 values (1,0),('a',1),('z',2);
+select f1 from t1 where f1 in (1,'z');
+select f2 from t1 where f2 in (1,'z');
+select f1 from t1 where 'z' in (1,f1);
+select * from t1 where 'z' in (f2,f1);
+select * from t1 where 1 in (f2,f1);
+drop table t1;
+
 # End of 4.1 tests
 
 #

sql/item_cmpfunc.cc

@@ -76,11 +76,19 @@ static void agg_cmp_type(THD *thd, Item_result *type, Item **items, uint nitems)
     field= NULL;
 
   type[0]= items[0]->result_type();
-  for (i= 1; i < nitems; i++)
+  /* Reset to 0 on first occurence of non-const item. 1 otherwise */
+  bool is_const= items[0]->const_item();
+
+  for (i= 1 ; i < nitems ; i++)
   {
-    type[0]= item_cmp_type(type[0], items[i]->result_type());
-    if (field && convert_constant_item(thd, field, &items[i]))
-      type[0]= INT_RESULT;
+    if (!items[i]->const_item())
+    {
+      type[0]= is_const ? items[i]->result_type() :
+                 item_cmp_type(type[0], items[i]->result_type());
+      is_const= 0;
+    }
+    else if (is_const)
+      type[0]= item_cmp_type(type[0], items[i]->result_type());
   }
 }