MySQL 触发器

• trigger
• new与old
  • 指代新数据
  • insert只有new是合法的；
  • delete只有old才合法；
  • update可同时使用。
• 语句
  • show triggers [from schema_name];
  • drop trigger [if exists] [schema_name.]trigger_name
• 例1

  • # 当更新表tb1的name字段时，更新表tb2 field1加上name的长度create trigger tr1
    after                   # before, after
    insert on tb1           # insert, update, delete
    for each row
    update tb2 set field1 = field1+char_length(new.name);
        

• 例2

  • # UPDATE同时使用NEW和OLD
    create trigger tr1
    before update on t22
    for each row
    begin
    set @old = old.s1;
    set @new = new.s1;
    end;