如何在同一查询中添加两条select命令的结果

Question

我目前有两条select命令，如下所示。我想要做的是将结果一起添加到SQL查询中，而不是代码中的变量。

select sum(hours) from resource; 
select sum(hours) from projects-time; 

是否有可能在同一个SQL中输出两个结果的总和？

Answer 1

是的。这是可能:D

SELECT SUM(totalHours) totalHours 
FROM 
     ( 
      select sum(hours) totalHours from resource 
      UNION ALL 
      select sum(hours) totalHours from projects-time 
     ) s 

一点题外话，表名projects-time必须限定，以避免语法错误。分隔符符号在您使用的RDBMS上有所不同。

Answer 2

一些简单的像这样可以在select子句中使用子查询来完成：

select ((select sum(hours) from resource) + 
     (select sum(hours) from projects-time) 
     ) as totalHours 

对于这样一个简单的查询，因为这，这样子查询是合理的。

在某些数据库中，您可能需要为查询编译添加from dual。

如果你想输出的每个单独：

select (select sum(hours) from resource) as ResourceHours, 
     (select sum(hours) from projects-time) as ProjectHours 

如果你想同时和的总和，一个子查询方便：

select ResourceHours, ProjectHours, (ResourceHours+ProjecctHours) as TotalHours 
from (select (select sum(hours) from resource) as ResourceHours, 
      (select sum(hours) from projects-time) as ProjectHours 
    ) t 

Answer 3

UNION ALL一次，一次聚集：

SELECT sum(hours) AS total_hours 
FROM (
    SELECT hours FROM resource 
    UNION ALL 
    SELECT hours FROM "projects-time" -- illegal name without quotes in most RDBMS 
    ) x 

Answer 4

重复多个聚合li柯 SELECT SUM（数量）从TOTAL_AMOUNT（ SELECT量TABLE_1 UNION ALL SELECT 量TABLE_2 UNION ALL SELECT 从ASSURED_SUM TABLE_3 .... ）

Answer 5

如果你想多操作使用

select (sel1.s1+sel2+s2) 

(select sum(hours) s1 from resource) sel1 
join 
(select sum(hours) s2 from projects-time)sel2 
on sel1.s1=sel2.s2