sql查询从两个不同的表中获取两列的总和

Question

I have two tables. I want to add all the values of one column from table 1 to all the values of a particular column of table 2. How to do that?

for example

table A

Id Name  Salary 
1    A   20000 
2    B   30000

table B

Id Name   Salary 
1    A    30000 
2    B    40000

I want the result as total salary= sum(salary of table A) + sum(salary of table B)

Here result should come as 120000

Answer 1

Do this with a subquery:

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

Or, if one of the tables could be empty, union all would be better:

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

Answer 2

Using a Union first. Try this query:

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