MySQL数据库中分组统计的问题

首先准备四张表A、B、C、D，

--------------------------------

A　     |　B　 |　C　  |　D

a   b   |   a   c   |   a   d   |   d   e

1   1   |   1   1   |   1   A   |   A   1

2   2   |   1   3   |   2   B   |   B   2

3   4   |   1   4   |   3   C   |   C   3

4   6   |   2   1   |   4   D   |   D   4

--------------------------------

下面我们需要用一条sql语句将A表所有的列，B表对与A表a字段相关联的列求count,通过C表,将D表与A表关联起来，得到的结果如下：

1   1   3   1

2   2   1   2

3   4   0   3

4   6   0   4

Mysql语句解决：

select A.a,A.b,IFNULL(c,0) as c,D.a

from (select 1 as a,2 as b union all

select 2 as a,2 as b union all

select 3 as a,4 as b union all

select 4 as a,6 as b) as A

left outer join

(select a,count(a) as c from(

select 1 as a,3 as c union all

select 1 as a,3 as c union all

select 1 as a,3 as c union all

select 2 as a,3 as c ) B group by a) as B

on A.a=B.a

join

(select 1 as a,'A' as d union all

select 2 as a,'B' as d union all

select 3 as a,'C' as d union all

select 4 as a,'D' as d ) as C

on A.a=C.a

join(select 1 as a,'A' as d union all

select 2 as a,'B' as d union all

select 3 as a,'C' as d union all

select 4 as a,'D' as d ) as D

on D.d=C.d

本文作者:相关阅读:

ASP3.0高级编程(二)

jQuery实现原理的模拟代码 -6 代码下载

两难的选择:充满Trick的CSS

让IE6、IE7、IE8支持CSS3的脚本

Microsoft SQL Server 2008 Express版本

JSP由浅入深(6)—— JSP声明

Linux下磁盘设备文件(sda,sdb,sdc….)变化问题

日期 时间js控件

保存CSS中的图片的几种方法

Sun&MySQL全球巡展中国站正式启动

简单的ASP分页代码(测试正确)

PHP中通过语义URL防止网站被攻击的方法分享

聊天室实现私聊(三)

AMD显卡最新Linux系统版本驱动大幅更新(图)