Made TIMESTAMP NULL columns without explicit DEFAULT value to be always

treated as DEFAULT NULL columns (independently from their position in
table).

(still to be discussed with Monty, Brian, Trudy et al. before push)


mysql-test/r/type_timestamp.result:
  Update test after making TIMESTAMP NULL columns without explicit 
  DEFAULT value to be always treated as DEFAULT NULL columns 
  (independently from their position in table).
mysql-test/t/type_timestamp.test:
  Update test after making TIMESTAMP NULL columns without explicit 
  DEFAULT value to be always treated as DEFAULT NULL columns 
  (independently from their position in table).
sql/sql_parse.cc:
  add_field_to_list(): made TIMESTAMP NULL columns without explicit 
  DEFAULT value to be always treated as DEFAULT NULL columns (independently
  from their position in table). This also simplifies code a bit.

mysql-test/r/type_timestamp.result

@@ -369,7 +369,7 @@ create table t1 (a timestamp null, b timestamp null);
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` timestamp NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
+  `a` timestamp NULL default NULL,
   `b` timestamp NULL default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 insert into t1 values (NULL, NULL);
@@ -378,7 +378,22 @@ insert into t1 values ();
 select * from t1;
 a	b
 NULL	NULL
-2001-09-09 04:46:57	NULL
+NULL	NULL
+drop table t1;
+create table t1 (a timestamp null default current_timestamp on update current_timestamp, b timestamp null);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` timestamp NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
+  `b` timestamp NULL default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+insert into t1 values (NULL, NULL);
+SET TIMESTAMP=1000000018;
+insert into t1 values ();
+select * from t1;
+a	b
+NULL	NULL
+2001-09-09 04:46:58	NULL
 drop table t1;
 create table t1 (a timestamp null default null, b timestamp null default '2003-01-01 00:00:00');
 show create table t1;

mysql-test/t/type_timestamp.test

@@ -236,9 +236,10 @@ drop table t1;
 
 #
 # Test for TIMESTAMP columns which are able to store NULLs
-# (Auto-set property should work for them and NULL values
-#  should be OK as default values)
 #
+
+# Unlike for default TIMESTAMP fields we don't interpret first field
+# in this table as TIMESTAMP with DEFAULT NOW() ON UPDATE NOW() properties.
 create table t1 (a timestamp null, b timestamp null);
 show create table t1;
 insert into t1 values (NULL, NULL);
@@ -247,6 +248,16 @@ insert into t1 values ();
 select * from t1;
 drop table t1;
 
+# But explicit auto-set properties still should be OK.
+create table t1 (a timestamp null default current_timestamp on update current_timestamp, b timestamp null);
+show create table t1;
+insert into t1 values (NULL, NULL);
+SET TIMESTAMP=1000000018;
+insert into t1 values ();
+select * from t1;
+drop table t1;
+
+# It is also OK to specify NULL as default explicitly for such fields.
 create table t1 (a timestamp null default null, b timestamp null default '2003-01-01 00:00:00');
 show create table t1;
 insert into t1 values (NULL, NULL);

sql/sql_parse.cc

@@ -4142,12 +4142,7 @@ bool add_field_to_list(THD *thd, char *field_name, enum_field_types type,
     }
     else if (default_value->type() == Item::NULL_ITEM)
     {
-      /*
-        TIMESTAMP type should be able to distingush non-specified default
-        value and default value NULL later.
-      */
-      if (type != FIELD_TYPE_TIMESTAMP)
-        default_value= 0;
+      default_value= 0;
       if ((type_modifier & (NOT_NULL_FLAG | AUTO_INCREMENT_FLAG)) ==
 	  NOT_NULL_FLAG)
       {
@@ -4357,19 +4352,27 @@ bool add_field_to_list(THD *thd, char *field_name, enum_field_types type,
       else
         new_field->unireg_check= (on_update_value?Field::TIMESTAMP_UN_FIELD:
                                                   Field::NONE);
-
-      if (default_value->type() == Item::NULL_ITEM)
-        new_field->def= 0;
     }
     else
     {
-      /* 
-        We are setting TIMESTAMP_OLD_FIELD here only temporary, we will 
-        replace this value by TIMESTAMP_DNUN_FIELD or NONE later when 
+      /*
+        If we have default TIMESTAMP NOT NULL column without explicit DEFAULT
+        or ON UPDATE values then for the sake of compatiblity we should treat
+        this column as having DEFAULT NOW() ON UPDATE NOW() (when we don't
+        have another TIMESTAMP column with auto-set option before this one)
+        or DEFAULT 0 (in other cases).
+        So here we are setting TIMESTAMP_OLD_FIELD only temporary, and will
+        replace this value by TIMESTAMP_DNUN_FIELD or NONE later when
         information about all TIMESTAMP fields in table will be availiable.
+
+        If we have TIMESTAMP NULL column without explicit DEFAULT value
+        we treat it as having DEFAULT NULL attribute.
       */
-      new_field->unireg_check= on_update_value?Field::TIMESTAMP_UN_FIELD:
-                                               Field::TIMESTAMP_OLD_FIELD;
+      new_field->unireg_check= on_update_value ?
+                               Field::TIMESTAMP_UN_FIELD :
+                               (new_field->flags & NOT_NULL_FLAG ?
+                                Field::TIMESTAMP_OLD_FIELD:
+                                Field::NONE);
     }
     break;
   case FIELD_TYPE_DATE:				// Old date type