Question

我们假设我们有3个表A，B和C，其中列district，population。{
我需要在单个查询中找到所有表中所有population的总和我对查询并不太熟悉，并且尚未建立结构，但想知道下面的查询是否有效。

select Sum(SUM1+SUM2+SUM3) 
from tableA A, tableB B, tableC C 
where SUM1 = sum(A.population) 
  and SUM2 = sum(B.population) 
  and SUM3 = sum(C.population) ;

欢迎任何其他建议。

Answer 1

您可以使用union all：

select sum(t.population)
from (
   select population from table A
   union all
   select population from table B
   union all
   select population from table A
) t

Answer 2

尝试：

SELECT COALESCE((SELECT SUM(population) FROM TableA),0) + 
       COALESCE((SELECT SUM(population) FROM TableB),0) +
       COALESCE((SELECT SUM(population) FROM TableC),0) AS TotalPopulation

Demo here

查找不同表格

2 个答案: