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 程式師世界 >> 數據庫知識 >> 其他數據庫知識 >> 更多數據庫知識 >> 淺談MySQL數據庫中如何解決分組統計的問題

淺談MySQL數據庫中如何解決分組統計的問題

編輯:更多數據庫知識

 首先准備四張表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

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