MDEV-9374 having '2015-01-01 01:00:00.000001' > coalesce(NULL) returns true

The problem was earlier fixed by the patch for MDEV-9521.
Adding tests only.

mysql-test/r/type_datetime.result

@@ -834,5 +834,13 @@ a	b	a	b
 DEALLOCATE PREPARE stmt1;
 DROP TABLE t1,t2;
 #
+# MDEV-9374 having '2015-01-01 01:00:00.000001' > coalesce(NULL) returns true
+#
+CREATE TABLE t1 (c1 DATETIME(0));
+INSERT INTO t1 VALUES (NULL);
+SELECT * FROM t1 HAVING '2015-01-01 01:00:00.000001' > COALESCE(c1);
+c1
+DROP TABLE t1;
+#
 # End of 5.5 tests
 #

mysql-test/t/type_datetime.test

@@ -610,6 +610,14 @@ EXECUTE stmt1;
 DEALLOCATE PREPARE stmt1;
 DROP TABLE t1,t2;
 
+--echo #
+--echo # MDEV-9374 having '2015-01-01 01:00:00.000001' > coalesce(NULL) returns true
+--echo #
+CREATE TABLE t1 (c1 DATETIME(0));
+INSERT INTO t1 VALUES (NULL);
+SELECT * FROM t1 HAVING '2015-01-01 01:00:00.000001' > COALESCE(c1);
+DROP TABLE t1;
+
 --echo #
 --echo # End of 5.5 tests
 --echo #