sql查询从两个不同的表中获取两列的总和

Question

我有两张桌子。我想将表1中一列的所有值添加到表2的特定列的所有值。如何做？

例如

表A

Id Name  Salary 
1    A   20000 
2    B   30000

表B

Id Name   Salary 
1    A    30000 
2    B    40000

我希望结果为total salary= sum(salary of table A) + sum(salary of table B)

此结果应为120000

Answer 1

使用子查询执行此操作：

select a.s + b.s
from (select sum(salary) as s from a) cross join
     (select sum(salary) as s from b);

或者，如果其中一个表可能为空，union all会更好：

select sum(salary)
from (select id, name, salary from a union all
      select id, name, salary from b
     ) ab;

Answer 2

首先使用联盟。试试这个问题：

select sum(salary) from 
(
select sum(Salary) as salary from tableA
union 
select sum(Salary) as salary from tableB
)