Bug#31990: MINUTE() and SECOND() return bogus results when used on a DATE

HOUR(), MINUTE(), ... returned spurious results when used on a DATE-cast.
This happened because DATE-cast object did not overload get_time() method
in superclass Item. The default method was inappropriate here and
misinterpreted the data.

Patch adds missing method; get_time() on DATE-casts now returns SQL-NULL
on NULL input, 0 otherwise. This coincides with the way DATE-columns
behave.

mysql-test/r/cast.result

@@ -414,4 +414,28 @@ NULL
 NULL
 20070719
 drop table t1;
+CREATE TABLE t1 (f1 DATE);
+INSERT INTO t1 VALUES ('2007-07-19'), (NULL);
+SELECT HOUR(f1),
+MINUTE(f1),
+SECOND(f1) FROM t1;
+HOUR(f1)	MINUTE(f1)	SECOND(f1)
+0	0	0
+NULL	NULL	NULL
+SELECT HOUR(CAST('2007-07-19' AS DATE)),
+MINUTE(CAST('2007-07-19' AS DATE)),
+SECOND(CAST('2007-07-19' AS DATE));
+HOUR(CAST('2007-07-19' AS DATE))	MINUTE(CAST('2007-07-19' AS DATE))	SECOND(CAST('2007-07-19' AS DATE))
+0	0	0
+SELECT HOUR(CAST(NULL AS DATE)),
+MINUTE(CAST(NULL AS DATE)),
+SECOND(CAST(NULL AS DATE));
+HOUR(CAST(NULL AS DATE))	MINUTE(CAST(NULL AS DATE))	SECOND(CAST(NULL AS DATE))
+NULL	NULL	NULL
+SELECT HOUR(NULL),
+MINUTE(NULL),
+SECOND(NULL);
+HOUR(NULL)	MINUTE(NULL)	SECOND(NULL)
+NULL	NULL	NULL
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/cast.test

@@ -246,4 +246,26 @@ INSERT INTO t1(d1) VALUES ('2007-07-19 08:30:00'), (NULL),
 SELECT cast(date(d1) as signed) FROM t1;
 drop table t1;
 
+#
+# Bug #31990: MINUTE() and SECOND() return bogus results when used on a DATE
+#
+
+# Show that HH:MM:SS of a DATE are 0, and that it's the same for columns
+# and typecasts (NULL in, NULL out).
+CREATE TABLE t1 (f1 DATE);
+INSERT INTO t1 VALUES ('2007-07-19'), (NULL);
+SELECT HOUR(f1),
+       MINUTE(f1),
+       SECOND(f1) FROM t1;
+SELECT HOUR(CAST('2007-07-19' AS DATE)),
+       MINUTE(CAST('2007-07-19' AS DATE)),
+       SECOND(CAST('2007-07-19' AS DATE));
+SELECT HOUR(CAST(NULL AS DATE)),
+       MINUTE(CAST(NULL AS DATE)),
+       SECOND(CAST(NULL AS DATE));
+SELECT HOUR(NULL),
+       MINUTE(NULL),
+       SECOND(NULL);
+DROP TABLE t1;
+
 --echo End of 5.0 tests

sql/item_timefunc.cc

@@ -2645,6 +2645,13 @@ bool Item_date_typecast::get_date(MYSQL_TIME *ltime, uint fuzzy_date)
 }
 
 
+bool Item_date_typecast::get_time(MYSQL_TIME *ltime)
+{
+  bzero((char *)ltime, sizeof(MYSQL_TIME));
+  return args[0]->null_value;
+}
+
+
 String *Item_date_typecast::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);

sql/item_timefunc.h

@@ -779,6 +779,7 @@ class Item_date_typecast :public Item_typecast_maybe_null
   const char *func_name() const { return "cast_as_date"; }
   String *val_str(String *str);
   bool get_date(MYSQL_TIME *ltime, uint fuzzy_date);
+  bool get_time(MYSQL_TIME *ltime);
   const char *cast_type() const { return "date"; }
   enum_field_types field_type() const { return MYSQL_TYPE_DATE; }
   Field *tmp_table_field(TABLE *t_arg)