Merge mysql.com:/home/hf/work/mrg/mysql-4.1-opt

into  mysql.com:/home/hf/work/mrg/mysql-5.0-opt

mysql-test/r/type_datetime.result

@@ -168,6 +168,9 @@ dt
 0000-00-00 00:00:00
 0000-00-00 00:00:00
 drop table t1;
+select cast('2006-12-05 22:10:10' as datetime) + 0;
+cast('2006-12-05 22:10:10' as datetime) + 0
+20061205221010.000000
 CREATE TABLE t1(a DATETIME NOT NULL);
 INSERT INTO t1 VALUES ('20060606155555');
 SELECT a FROM t1 WHERE a=(SELECT MAX(a) FROM t1) AND (a="20060606155555");

mysql-test/t/type_datetime.test

@@ -113,6 +113,12 @@ insert into t1 values ("00-00-00"), ("00-00-00 00:00:00");
 select * from t1;
 drop table t1;
 
+#
+# Bug #16546 DATETIME+0 not always coerced the same way 
+#
+select cast('2006-12-05 22:10:10' as datetime) + 0;
+
+
 # End of 4.1 tests
 
 #

sql/item_timefunc.h

@@ -847,12 +847,19 @@ public:
   String *val_str(String *str);
   const char *cast_type() const { return "datetime"; }
   enum_field_types field_type() const { return MYSQL_TYPE_DATETIME; }
+  void fix_length_and_dec()
+  {
+    Item_typecast_maybe_null::fix_length_and_dec();
+    decimals= DATETIME_DEC;
+  }
+
   Field *tmp_table_field(TABLE *t_arg)
   {
     return (new Field_datetime(maybe_null, name, t_arg, &my_charset_bin));
   }
   bool result_as_longlong() { return TRUE; }
   longlong val_int();
+  double val() { return (double) val_int(); }
   my_decimal *val_decimal(my_decimal *decimal_value)
   {
     DBUG_ASSERT(fixed == 1);