Backport of fix to bug #33629 into mysql-next-mr-bugfixing.

Bug #33629: last_day function can return null, but has 'not null' flag set for result

LAST_DAY and MAKEDATE functions are documented as
returning NULL value, but actually they was implemented
as returning NOT NULL typed values.

That caused a confusing error "ERROR 1048 (23000): Column
'...' cannot be null" on queries like: 

  SELECT 1 FROM (SELECT LAST_DAY('0')) a;


mysql-test/r/func_sapdb.result:
    Updated test case for bug #33629.
mysql-test/r/func_time.result:
    Updated test case for bug #33629.
mysql-test/r/type_date.result:
    Added test case for bug #33629.
mysql-test/t/type_date.test:
    Added test case for bug #33629.
sql/item_timefunc.h:
    Bug #33629: last_day function can return null, but has 'not null' flag set for result
    
    1. The Item_func_makedate::fix_length_and_dec method
       has been modified to declare MAKEDATE() as a function
       returning nullable value.
    2. The Item_func_last_day::fix_length_and_dec method
       has been overloaded for the same purpose.

mysql-test/r/func_sapdb.result

@@ -194,7 +194,7 @@ date("1997-12-31 23:59:59.000001") as f8,
 time("1997-12-31 23:59:59.000001") as f9;
 describe t1;
 Field	Type	Null	Key	Default	Extra
-f1	date	NO		0000-00-00	
+f1	date	YES		NULL	
 f2	datetime	YES		NULL	
 f3	time	YES		NULL	
 f4	time	YES		NULL	

mysql-test/r/func_time.result

@@ -814,7 +814,7 @@ create table t1 select last_day('2000-02-05') as a,
 from_days(to_days("960101")) as b;
 describe t1;
 Field	Type	Null	Key	Default	Extra
-a	date	NO		0000-00-00	
+a	date	YES		NULL	
 b	date	YES		NULL	
 select * from t1;
 a	b

mysql-test/r/type_date.result

@@ -276,3 +276,25 @@ a
 0000-00-01
 drop table t1;
 End of 5.1 tests
+#
+# Bug #33629: last_day function can return null, but has 'not null'
+#             flag set for result
+#
+SELECT 1 FROM (SELECT LAST_DAY('0')) a;
+1
+1
+Warnings:
+Warning	1292	Incorrect datetime value: '0'
+SELECT 1 FROM (SELECT MAKEDATE(2011,0)) a;
+1
+1
+CREATE TABLE t1 AS
+SELECT LAST_DAY('1970-01-01') AS f1,
+MAKEDATE(1970, 1)      AS f2;
+DESCRIBE t1;
+Field	Type	Null	Key	Default	Extra
+f1	date	YES		NULL	
+f2	date	YES		NULL	
+DROP TABLE t1;
+#
+End of 6.0 tests

mysql-test/t/type_date.test

@@ -247,3 +247,21 @@ select * from t1 where a between '0000-00-01' and '0000-00-02';
 drop table t1;
 
 --echo End of 5.1 tests
+
+--echo #
+--echo # Bug #33629: last_day function can return null, but has 'not null'
+--echo #             flag set for result
+--echo #
+
+SELECT 1 FROM (SELECT LAST_DAY('0')) a;
+SELECT 1 FROM (SELECT MAKEDATE(2011,0)) a;
+
+CREATE TABLE t1 AS
+  SELECT LAST_DAY('1970-01-01') AS f1,
+         MAKEDATE(1970, 1)      AS f2;
+DESCRIBE t1;
+DROP TABLE t1;
+
+--echo #
+
+--echo End of 6.0 tests

sql/item_timefunc.h

@@ -871,6 +871,7 @@ class Item_func_makedate :public Item_date_func
   { 
     decimals=0;
     max_length=MAX_DATE_WIDTH*MY_CHARSET_BIN_MB_MAXLEN;
+    maybe_null= 1;
   }
   longlong val_int();
 };
@@ -1025,4 +1026,9 @@ class Item_func_last_day :public Item_date
   Item_func_last_day(Item *a) :Item_date(a) {}
   const char *func_name() const { return "last_day"; }
   bool get_date(MYSQL_TIME *res, uint fuzzy_date);
+  void fix_length_and_dec()
+  { 
+    Item_date::fix_length_and_dec();
+    maybe_null= 1;
+  }
 };