我有两个应收帐款表＆
表：应收款
tranId roll month amount
1 1111 October-2019 10
2 1112 October-2019 10
3 1113 October-2019 10
4 1114 October-2019 10
5 1115 October-2019 10
表格：接收
tranId roll month amount
1 1111 October-2019 10
2 1111 September-2019 10
3 1113 October-2019 10
4 1114 October-2019 10
5 1115 October-2019 10
6 1116 October-2019 10
7 1117 October-2019 10
8 1118 October-2019 10
9 1119 October-2019 10
10 1120 October-2019 10
在两个表月份列中都是字符串，并且表接收卷+月份列是唯一的。我想从诸如此类的表格中创建一个学生的应收账款和收款报表（其中roll = 1111）。
预期结果：
month rcvamount rcvvmonth rcvvamount
---------------------------------------------------------
October-2019 10 October-2019 10
---------------------------------------------------------
September-2019 10 - -
我的查询是：
SELECT receive.month, sum(receive.amount) AS rcvamount, receivable.month AS rcvvmonth,
receivable.amount AS rcvvamount
FROM receive
LEFT JOIN receivable ON receive.month = receivable.month
WHERE receive.roll = 1111
GROUP BY receive.month
结果是：
month rcvamount rcvvmonth rcvvamount
----------------|-------|----------------------------------
October-2019 | 50 | October-2019 10
----------------|-------|----------------------------------
September-2019 10 - -
2019年10月的revmount应该是接收表中的10。
答案 0 :(得分：1)
您可以在加入之前 进行汇总。或使用union all进行汇总：
SELECT month, SUM(ramount) AS rcvamount,
SUM(raamount) AS rcvvamount
FROM ((SELECT month, amount as ramount, null as raamount
FROM receive
WHERE roll = 1111
) UNION ALL
(SELECT month, NULL as ramount, amount as raamount
FROM receiveable
WHERE roll = 1111
)
) r
GROUP BY month;
UNION ALL的一个不错的功能是它可以处理任一表中的丢失数据。