获取具有多个连接的多列总和时如何防止重复

Question

假设我有 3 个表：发票、费用和付款。 发票可以有多项费用，费用可以有多次付款。

做一个简单的连接，数据看起来像这样：

invoiceid  |   chargeid   |  charge   |  payment
----------------------------------
1          |      1       |    50     |   50
2          |      2       |    100    |   25
2          |      2       |    100    |   75
2          |      3       |    30     |   10
2          |      3       |    30     |   5

如果我加入总和，

select invoiceid, sum(charge), sum(payment)
from invoices i 
inner join charges c on i.invoiceid = c.invoiceid
inner join payments p on p.chargeid = c.chargeid
group by invoiceid

付款总和是正确的，但费用会重复：

invoiceid  |    charges   |   payments
--------------------------------------
1          |     50       |     50
2          |     260      |     115

我想要一个查询来获取发票列表，其中包含每张发票的付款总和和费用总和，如下所示：

invoiceid  |    charges   |   payments
--------------------------------------
1          |     50       |     50
2          |     130      |     115

有没有办法通过修改上面的查询而不使用子查询来做到这一点，因为在处理大量数据时子查询可能会非常慢？ 我觉得必须有一种方法可以只在总和中包含独特的费用。

Answer 1

一种方法是在连接分组值之前通过表进行聚合

SELECT i.invoiceid, SumOfCharge, SumOfInvoice
FROM  invoices i 
INNER JOIN  (SELECT InvoiceID, suM(charges) sumOfCharges 
            FROM charges c 
            GROUP BY Invoiceid) c
   on i.invoiceid = c.invoiceid
INNER JOIN (SELECT invoiceid, sum(payment) as SumOfPayment
            FROM charages c
            INNER JOIN payments p on p.chargeid = c.chargeid
            GROUP BY Invoiceid) P
   on i.invoiceID = p.invoiceid

另一种方法是使用相关性对每张发票进行内联

SELECT i.invoiceid
     , (SELECT SUM(charge) FROM charges c WHERE c.invoiceid = i.invoiceid) SumOfCharge
     , SUM(Payment) SumOfInvoice
FROM  invoices i 
INNER JOIN  charges c 
   on i.invoiceid = c.invoiceid
INNER JOIN payments p 
   on p.chargeid = c.chargeid
GROUP BY Invoiceid

Answer 2

您还可以通过使用 LATERAL JOINS 来实现此目的

   SELECT
     i.invoiceid,
     chgs.total_charges,
     pays.total_payments
   FROM
     invoices AS i
     JOIN LATERAL (
        SELECT
            SUM( charge ) AS total_charges
        FROM
            charges AS c
        WHERE
            c.invoiceid = i.invoiceid
     ) AS chgs ON TRUE
     JOIN LATERAL (
        SELECT
            SUM( payment ) AS total_payments
        FROM
            payments AS p
        WHERE
            p.chargeid = c.chargeid
     ) AS pays ON TRUE

Answer 3

我希望这将有所帮助。

select invoiceid, sum(distinct charge)as charges, sum(payment)as payments from yourtable group by invoiceid;