Question

按月计算公司利润，计算公司利润如下： sum of incoming minus outgoing。

表：

传入（金额，月份）
传出（金额，月份）

数据类型：

月整数，范围1-12
金额整数

我试过

SELECT month,tsum-bsum FROM
(SELECT month,SUM(amount) tsum FROM incoming GROUP BY month
FULL OUTER JOIN
    (SELECT month,SUM(amount) bsum FROM outgoing GROUP BY month)
)
ON incoming.month=outgoing.month;

但是加入后月份可以为空，这会导致tsum-bsum出现问题。

Answer 1

这里是示例查询

SELECT COALESCE(in.month, out.month) as month, sum(COALESCE(in.amount,0) - COALESCE(out.amount,0)) as profit
FROM
    incoming as in
FULL OUTER JOIN
    outgoing as out
ON in.month = out.month;
GROUP BY COALESCE(in.month, out.month)

Answer 2

使用coalesce()：

SELECT coalesce(i.month, o.month) as month, i.tsum - o.bsum
FROM (SELECT month, SUM(amount) as tsum FROM incoming GROUP BY month) i
     FULL OUTER JOIN
     (SELECT month, SUM(amount) as bsum FROM outgoing GROUP BY month) o
     ON i.month = o.month;

请注意，如果值为NULL，差异可能为NULL，因此您可能需要：

SELECT coalesce(i.month, o.month) as month,
       coalesce(i.tsum, 0) - coalesce(o.bsum, 0) as diff
FROM (SELECT month, SUM(amount) as tsum FROM incoming GROUP BY month) i
     FULL OUTER JOIN
     (SELECT month, SUM(amount) as bsum FROM outgoing GROUP BY month) o
     ON i.month = o.month;

完全外部联接与group by query

2 个答案: