Question

我有以下4个相同的选择，返回相同的列输出，结果不同。

类似的东西：

1）select a, count(*) from table a;

2）select a, count(*) from table b;

3）select a, count(*) from table c;

4）select a, count(*) from table d;

他们都输出如下内容：

=================
a     |count(*) (Table a)| 
=================
hi    | 2
hello | 3    
why   | 4

=================
a     |count(*) (Table b)| 
=================
hi    | 4
hello | 6
why   | 8

类似于表c和d。

我想在所有这四个表上进行连接，以便我可以获得一个表，其中相同的列被求和并分组并显示为一个，像这样的东西

=================
a     |count(*) (Table a & b union )| 
=================
hi    | 6
hello | 9
why   | 12

我已经找到了一个适用于两个表的查询，但是桌面上的其他联合不能很好地运行：

select a, sum(total) from (select a, count(*) from table a union all select a, count(*) from table b) as T group by a;

这适用于两张桌子但不超过我错过的内容。

Answer 1

select a,
   sum(total) from
    (select a, count(*) AS total from table a 
        union all 
    select a, count(*) AS total from table b
        union all
    select a, count(*) AS total from table c 
        union all 
    select a, count(*) AS total from table d 
        union all 
    )
    group by a

Answer 2

您需要在执行以下计算之前完成工作

select a, count(*) from
(
select a from table a 
union all 
select a from table b
union all 
select a from table c
union all 
select a from table d
) as T
group by a

将多个相同的select语句连接成一个（JOIN或UNION）？

2 个答案: