MDEV-17299 Assertion `maybe_null' failed in make_sortkey

mysql-test/r/type_date.result

@@ -854,5 +854,30 @@ d	COUNT(*)
 NULL	2
 DROP TABLE t1;
 #
+# MDEV-17299 Assertion `maybe_null' failed in make_sortkey
+#
+CREATE TABLE t1 (pk int NOT NULL, d1 date, d2 date NOT NULL);
+INSERT INTO t1 values (1,'2018-06-22','2018-06-22'),(2,'2018-07-11','2018-07-11');
+CREATE VIEW v1 AS SELECT * FROM t1;
+SELECT group_concat(d1/(CASE 'b' WHEN 'j' THEN 'c' END))
+FROM v1 GROUP BY greatest(pk, 0, d2);
+group_concat(d1/(CASE 'b' WHEN 'j' THEN 'c' END))
+NULL
+Warnings:
+Warning	1292	Incorrect datetime value: '1' for column 'pk' at row 1
+Warning	1292	Incorrect datetime value: '2' for column 'pk' at row 1
+Warning	1292	Incorrect datetime value: '1' for column 'pk' at row 1
+Warning	1292	Incorrect datetime value: '1' for column 'pk' at row 1
+Warning	1292	Incorrect datetime value: '2' for column 'pk' at row 2
+CREATE TABLE t2 AS SELECT greatest(pk, 0, d2) AS c1 FROM t1 LIMIT 0;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `c1` date DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+DROP VIEW v1;
+DROP TABLE t1;
+#
 # End of 10.1 tests
 #

mysql-test/t/type_date.test

@@ -585,6 +585,20 @@ INSERT INTO t1 VALUES ('1985-05-13'),('1989-12-24');
 SELECT d, COUNT(*) FROM t1 GROUP BY d WITH ROLLUP HAVING CASE d WHEN '2017-05-25' THEN 0 ELSE 1 END;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-17299 Assertion `maybe_null' failed in make_sortkey
+--echo #
+
+CREATE TABLE t1 (pk int NOT NULL, d1 date, d2 date NOT NULL);
+INSERT INTO t1 values (1,'2018-06-22','2018-06-22'),(2,'2018-07-11','2018-07-11');
+CREATE VIEW v1 AS SELECT * FROM t1;
+SELECT group_concat(d1/(CASE 'b' WHEN 'j' THEN 'c' END))
+  FROM v1 GROUP BY greatest(pk, 0, d2);
+CREATE TABLE t2 AS SELECT greatest(pk, 0, d2) AS c1 FROM t1 LIMIT 0;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+DROP VIEW v1;
+DROP TABLE t1;
 
 --echo #
 --echo # End of 10.1 tests

sql/item_func.cc

@@ -2794,6 +2794,8 @@ void Item_func_min_max::fix_length_and_dec()
   switch (tmp_cmp_type) {
   case TIME_RESULT:
     // At least one temporal argument was found.
+    if (temporal_type_count < arg_count)
+      maybe_null= true; // Non-temporal-to-temporal conversion can return NULL
     collation.set_numeric();
     set_handler_by_field_type(temporal_field_type);
     if (is_temporal_type_with_time(temporal_field_type))