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分类: Mysql/postgreSQL

2008-05-14 16:01:22

 来自:
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
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