Question

我有一个SQL表，其中包含以下列：发票ID，债务人ID，发票日期和发票金额。发票ID是唯一的。

我正在尝试创建一个具有平均发票金额的额外列。因此，我希望每行要债务人的平均发票金额，但只需要发票日期<=列的发票日期的发票。

我不确定从哪里开始，欢迎所有想法

Answer 1

尝试一下-

SELECT 
A.Invoice_ID, 
A.debtor_ID, 
A.invoice_date,
A.invoice_amount,
(
    SELECT AVG(B.invoice_amount) 
    FROM your_table B 
    WHERE B.debtor_ID = A.debtor_ID
    AND B.invoice_date <= A.invoice_date
) AS average_invoice_amount
FROM your_table A

Answer 2

You want to use window functions:

select t.*,
       avg(invoice_amount) over (partition by debtor_id order by invoice_date) as running_average
from t;

I strongly recommend this over a correlated subquery because it should be much faster -- even if you attempt to optimize the correlated subquery with indexes.

选择每个债务人的AVG（发票金额），其中date <日期行

2 个答案: