存在actor表，包含如下列信息：

    1. CREATE TABLE IF NOT EXISTS actor (
    2. actor_id smallint(5) NOT NULL PRIMARY KEY,
    3. first_name varchar(45) NOT NULL,
    4. last_name varchar(45) NOT NULL,
    5. last_update timestamp NOT NULL DEFAULT (datetime('now','localtime')));

    现在在last_update后面新增加一列名字为create_date, 类型为datetime, NOT NULL，默认值为’0000-00-00 00:00:00’

    1. alter table actor 
    2. add
    3. create_date datetime NOT NULL default '0000-00-00 00:00:00'