创建一个actor表，包含如下列信息

create table actor (
    actor_id smallint(5) not null primary key,
    first_name varchar(45) not null,
    last_name varchar(45) not null,
    last_update timestamp not null default (datetime('now','localtime'))
)

create table actor (
    actor_id smallint(5) not null primary key comment '主键id',
    first_name varchar(45) not null comment '名字',
    last_name varchar(45) not null comment '姓氏',
    last_update timestamp not null comment '最后更新时间，默认是系统的当前时间'
)