T-SQL（三）创建触发器

数据源
pubs 示例数据库

目标
创建 authors 表的日志表，记录修改city 列时的用户、新值、旧值、时间

代码

-- 创建修改日志
create table authors_log(
  username varchar(50),
  before_city varchar(20),
  after_city varchar(20),
  update_time datetime
)

-- 创建触发器
create trigger authors_update_trigger on authors
  for update
  as
  declare @t_before_city varchar(20);
  declare @t_after_city varchar(20);
  begin
    if(update(city))
      begin
        select @t_before_city = city from deleted;
        select @t_after_city = city from inserted;
        insert into authors_log values(user, @t_before_city, @t_after_city, getdate());
      end
  end

-- 测试触发器
update authors set city = 'changchun' where city = 'changchun'