MySQL数据库中如何解决分组统计的问题 - MySQL

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

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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

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