如何对两个相关表中的列求和

Question

我有两张桌子。 Invoices 和 invoice_items。我试图为每个客户获取total_payment 的总和和quantity 的总和。我试过这个查询：

SELECT client_id,
sum(total_amount), sum(it.quantity) as days_hired
FROM  `invoices` `iv`
  join invoice_items it on  it.invoice_id=iv.invoice_id
group by client_id, it.invoice_id

但对于 client_id 14，我得到的总付款为 1908 而不是 636。看起来此列的总和对于每个 invoie_item 都会重复。任何帮助将不胜感激。

invoices

invoice_id    client_id    total_payment
    36        13           530
    38        14           636


invoice_items

invoice_id    user_id      quantity     
36            2            2
38            3            2
38            4            2
38            5            2

预期输出：

13     530       2
14     636       6

Answer 1

你可以试试下面-

SELECT client_id, sum(total_amount) as toal_amount, sum(it.quantity) as total_quantity
FROM  `invoices` `iv`
join
(
 select invoice_id,sum(quantity) as quantity from invoice_items group by invoice_id
)it on  it.invoice_id=iv.invoice_id
group by client_id, it.invoice_id

Answer 2

试试：

select i.*, ii.total_quantity
from invoices i
join (
  select invoice_id, sum(quantity) total_quantity from invoice_items
  group by invoice_id
) ii on i.invoice_id = ii.invoice_id