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MYSQL 中的 浅谈MySQL数据库中如何解决分组统计的问题
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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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