MDEV-5459 Illegal mix of collations for datetime

mysql-test/r/ctype_cp1251.result

@@ -3282,5 +3282,15 @@ SELECT COALESCE(IF(test1=1, NULL, 1), test2) FROM t1;
 COALESCE(IF(test1=1, NULL, 1), test2)
 DROP TABLE t1;
 #
+# MDEV-5459 Illegal mix of collations for datetime
+#
+SET NAMES cp1251;
+CREATE TABLE t1 (dt DATETIME);
+INSERT INTO t1 VALUES ('2014-01-02 10:20:30');
+SELECT date(dt) FROM t1 WHERE (CASE WHEN 1 THEN date(dt) ELSE null END >= '2013-12-01 00:00:00');
+date(dt)
+2014-01-02
+DROP TABLE t1;
+#
 # End of 5.5 tests
 #

mysql-test/t/ctype_cp1251.test

@@ -95,6 +95,14 @@ SELECT COALESCE(IF(test1=1, 1, NULL), test2) FROM t1;
 SELECT COALESCE(IF(test1=1, NULL, 1), test2) FROM t1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-5459 Illegal mix of collations for datetime
+--echo #
+SET NAMES cp1251;
+CREATE TABLE t1 (dt DATETIME);
+INSERT INTO t1 VALUES ('2014-01-02 10:20:30');
+SELECT date(dt) FROM t1 WHERE (CASE WHEN 1 THEN date(dt) ELSE null END >= '2013-12-01 00:00:00');
+DROP TABLE t1;
 
 --echo #
 --echo # End of 5.5 tests

sql/item_cmpfunc.cc

@@ -549,8 +549,8 @@ void Item_bool_func2::fix_length_and_dec()
   */
 
   DTCollation coll;
-  if (args[0]->result_type() == STRING_RESULT &&
-      args[1]->result_type() == STRING_RESULT &&
+  if (args[0]->cmp_type() == STRING_RESULT &&
+      args[1]->cmp_type() == STRING_RESULT &&
       agg_arg_charsets_for_comparison(coll, args, 2))
     return;