sql - Oracle相关子查询问题

Question

我有以下架构

Invoices
=================
invoice_number
account_id
invoice_amount
invoice_date
status ("Paid","Not Paid")

我正在尝试编写查询以获取包含以下信息的所有发票...

• 发票号码
• 发票日期
• 帐户ID
• 发票金额
• 此帐户 ID 的最后支付发票金额（此行的发票日期之前）

我对最后一项（最后支付的发票金额）有疑问。到目前为止，我已经...

select 
inv2.invoice_number,
inv2.invoice_date,
inv2.account_id,
inv2.invoice_amount,
(
select * from (
    select inv.invoice_amount
      from invoices inv
      where inv.account_id = inv2.account_id
      and inv.status = 'PAID'
      and inv.invoice_date < inv2.invoice_date
      order by inv.invoice_date desc
    )
where rownum <=1
) as last_paid_amount
from
invoices inv2

我正在尝试重构它以不使用相关子查询，因为我的数据集的大小使得这非常昂贵。如何重构以使用不相关的子查询。这甚至可能吗？

谢谢你

Answer 1

我可能在这里搞砸了order by子句，因为我现在没有机会测试它，但想法是使用 LAG 函数：

select 
  inv2.invoice_number,
  inv2.invoice_date,
  inv2.account_id,
  inv2.invoice_amount,
  lag(invoice_amount) over(
    partiton by account_id 
    order by invoice_date, decode(status, 'PAID', 1, 0)  
  ) last_paid_amount
from
invoices inv2

Answer 2

select a.*, case when rnk = 1 then invoice_amount end as last_paid_amount
from(select 
inv2.invoice_number,
inv2.invoice_date,
inv2.account_id,
inv2.invoice_amount,
row_number() over(partition by invoice_number, account_id, (case when status = 'PAID' then 0 else 1 end), invoice_date desc) as rnk
from
invoices inv2) a

顺便说一句，我不确定 LAG 是否会在这里工作。