select * from B as bwhere b.BillNum in (select b.BillNum from Bgroup by b.BillNum having count(1) > 1)
--------------------------------------
id(int) cost(int) des Autoid(id)
--------------------------------------
1 10 aaaa 1
1 15 bbbb 2
1 20 cccc 3
2 80 aaaa 4
2 100 bbbb 5
2 60 dddd 6
3 500 dddd 7
--------------------------------------
取每一类id中cost最大的纪录
在上一节中我们们安装了mysql以及navicat，并掌握了如何创建库、创建表、修改表和插入、删除以及更新
数据
。这一节我们将继续学习SQL的简单
查询
语句。一、基本的
查询
语句1、select子句和from子句select <列名1>,<列名2>...
from <表名>；
select *
from <表名>；（查看全部列）
查询
语句的运行过程如图2、...
select count(*) as U from (select count(*) as c from test.user group by b)as t where t.c >=2;
select count(*) from (select count(*) from test.`user` group by b having count(*)>=2) as t ;
