MySql 怎么实现级联查询

首先能实现目的的语法是这么写：

select id,name,a_rankfrom table_a,(select a_id,count(*) as a_rankfrom table_bgroup by a_id)where table_a.id = table_b.a_idorder by a_rank

mysql:

1、先给B表添加主键列

alter table tableB add constraint b_PK primary key(date,channel)

2、将B表的组合主键关联到A表的外键组合键中

alter table tableB add constraint tableB_fk foreign key(date,channel) references tableA (date,channel) on DELETE CASCADE

3 delete from tableA where date =? and channel =? 就出发相关记录··~

create trigger update_id on a

for delete

as

Declare @qqlx_bid varchar(20)

Declare @qqlx_cid varchar(20)

--获得删除记录

select @qqlx_bid=bid,@qqlx_cid=cid from deleted

update b set bid=0 where bid=@qqlx_bid

update c set cid=0 where cid=@qqlx_cid

end

go

---