如何获得多行的 table a 和 table b 的总和

Question

我有两个表：

表 1 作为

id	date	customer	amount
1	2021-04-08	a	2
2	2021-04-08	a	3

表 2 作为 b

id	orderid	money
1	1	50
2	1	60
3	2	10
4	2	20

现在我想要日期、客户和表 1 中的金额总和以及表 2 中的金额总和。这意味着，结果应如下所示：

date	customer	amount	money
2021-04-08	a	5	140

但是通过以下查询我得到了 10 的数量：

 select
      a.date,
      a.customer,
      sum(b.money) as money,       
      sum(a.amount) as amount
  from table1 a
    left join table2 b on a.id = b.orderid   
  group by date, customer

不知道怎么解决。

Answer 1

这很棘手。您需要聚合 before joining:

select a.date, a.num_customer, a.a_amount, b.b_amount
from (select a.date, count(*) as num_customer, sum(a.amount) as a_amount
      from table1 a
      group by a.date
     ) a left join
     (select a.date, sum(b.amount) as b_amount
      from table1 a join
           table2 b
           on a.id = b.orderid
      group by a.date
     ) b
     on a.date = b.date;

另一种方法是先通过orderid聚合第二个table，然后再次加入并聚合：

select a.date, count(*) as num_customer, sum(a.amount),
       sum(b.b_amount)
from table1 a left join
     (select b.orderid, sum(b.amount) as b_amount
      from table2 b
      group by b.orderid
     ) b
     on a.id = b.orderid
group by a.date

如何获得多行的 table a 和 table b 的总和

How to get sum of table a and sum of table b with multiple rows

sql

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