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>