alter table table1 add order_date datetime null;

 

mysql> select * from table1;+----------+------------+-----+------------+| name_new | transactor | pid | order_date |+----------+------------+-----+------------+| 1hahha   | 1xiaohong  |   1 | NULL       || 2hahha   | 2xiaohong  |   2 | NULL       || 3hahha   | 3xiaohong  |   3 | NULL       || 4hahha   | 4xiaohong  |   4 | NULL       || 3hahha   | bob        |   5 | NULL       || 3hahha   | lee        |   6 | NULL       |+----------+------------+-----+------------+6 rows in set (0.00 sec)