首先准備四張表A、B、C、D，
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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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下面我們需要用一條sql語句將A表所有的列，B表對與A表a字段相關聯的列求count,通過C表,將D表與A表關聯起來，得到的結果如下：
1 1 3 1
2 2 1 2
3 4 0 3
4 6 0 4
Mysql語句解決：
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
