（mysql）我怎样才能得到总和？答案

【问题标题】：(mysql) how can i get sum of sum?（mysql）我怎样才能得到总和？
【发布时间】：2021-05-15 19:29:28
【问题描述】：

(select sum(serreq_totalamount)
                from servicerequirement
                    group by key_id)+
            (select sum(facreq_totalamount)
                from facilityrequirement
                    group by key_id)+
            (select sum(resorder_totalamount)
                from restaurantorder
                    group by key_id)

我想得到总和。如我所愿。

如何创建一个将这三个表的总和列相加的列？

首先，3太难了，所以我试了2个表，但是报错了。

select (
(select sum(serreq_totalamount)
        from servicerequirement
            group by servicerequirement.key_id)+
(select sum(facreq_totalamount)
        from facilityrequirement
            group by facilityrequirement.key_id));

Error Code: 1242. Subquery returns more than 1 row  0.000 sec

连接也是如此。

(select
(select sum(serreq_totalamount)
        from servicerequirement
            group by servicerequirement.key_id),
    (select sum(facreq_totalamount)
        from facilityrequirement
            group by facilityrequirement.key_id)
        from servicerequirement
    inner join facilityrequirement
    on servicerequirement.key_id=facilityrequirement.key_id);

Error Code: 1242. Subquery returns more than 1 row  0.000 sec

如果有人帮助我，我会很高兴。

【问题讨论】：

标签： mysql sum subquery

【解决方案1】：

您必须进行 suqueries 并通过 key_id 加入它们

然后你可以添加它们

SELECT t1.key_id,s1+s2+s3
FROM
(select key_id,sum(serreq_totalamount) s1
                from servicerequirement
                    group by key_id) t1
INNER JOIN 
            (select key_id,sum(facreq_totalamount) s2
                from facilityrequirement
                    group by key_id) t2 ON t1.key_id = t2.key_id
INNER JOIN
            (select key_id,sum(resorder_totalamount)
                from restaurantorder
                    group by key_id) t3 ON t2.key_id = t3.key_id

【讨论】：