MySQL数据库中分组统计的问题_MySQL

首先准备四张表A、B、C、D，

<p>--------------------------------     <br>A　     |　B　 |　C　  |　D     <br>a   b   |   a   c   |   a   d   |   d   e     <br>1   1   |   1   1   |   1   A   |   A   1     <br>2   2   |   1   3   |   2   B   |   B   2     <br>3   4   |   1   4   |   3   C   |   C   3     <br>4   6   |   2   1   |   4   D   |   D   4     <br>--------------------------------<br></p>

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：

<p>1   1   3   1     <br>2   2   1   2     <br>3   4   0   3     <br>4   6   0   4<br></p>

 

Mysql语句解决：

<p>select A.a,A.b,IFNULL(c,0) as c,D.a <br>from (select 1 as a,2 as b union all<br>select 2 as a,2 as b union all<br>select 3 as a,4 as b union all<br>select 4 as a,6 as b) as A <br>left outer join     <br>(select a,count(a) as c from(<br>select 1 as a,3 as c union all<br>select 1 as a,3 as c union all<br>select 1 as a,3 as c union all<br>select 2 as a,3 as c ) B group by a) as B<br>on A.a=B.a <br>join <br>(select 1 as a,'A' as d union all<br>select 2 as a,'B' as d union all<br>select 3 as a,'C' as d union all<br>select 4 as a,'D' as d ) as C <br>on A.a=C.a <br>join(select 1 as a,'A' as d union all<br>select 2 as a,'B' as d union all<br>select 3 as a,'C' as d union all<br>select 4 as a,'D' as d ) as D<br>on D.d=C.d<br></p>