Question

我有一张表，其记录仅对应于贷款的具体日期和贷款 - 即每笔贷款两笔记录。

Loans

Loan ID | Month     | Rate  | Action
--------------------------------
1       | 5/1/2000  | 5.50% | New
1       | 9/1/2000  | 6.00% | Closed
2       | 3/1/2000  | 5.25% | New
2       | 5/2/2000  | 5.50% | Closed

我还有另一个关于每个日期利率的记录。

Interest rates

Month       | Rate
--------------------
1/1/2000    | 5.00%
2/1/2000    | 5.25%
3/1/2000    | 5.25%
4/1/2000    | 5.25%
5/1/2000    | 5.50%
6/1/2000    | 5.50%
7/1/2000    | 5.50%
8/1/2000    | 6.00%
9/1/2000    | 6.00%
10/1/2000   | 6.50%

我想在取出和偿还给定贷款之间插入贷款表中缺少日期的行（以及相应的利率）。鉴于需要为每笔贷款插入中间日期，我无法通过LEFT JOIN，MERGE等解决这个问题。

预期结果：

Loan ID | Month     | Rate  | Action
---------------------------------
1       | 5/1/2000  | 5.50% | New
1       | 6/1/2000  | 5.50% | NULL
1       | 7/1/2000  | 5.50% | NULL
1       | 8/1/2000  | 6%    | NULL
1       | 9/1/2000  | 6%    | Closed
2       | 3/1/2000  | 5.25% | New
2       | 4/1/2000  | 5.25% | NULL
2       | 5/1/2000  | 5.50% | Closed

Answer 1

你的设计很难做到，你没有说出你正在使用的数据库。这是SQL服务器的示例（查询也适用于postgreSQL）：

<a href="firebug-2.0.18-fx.xpi"
hash="sha1:C7AF7F925C611EC88979FD905943584A2A891420"
onclick="return install(event);">Install Extension!</a>

Answer 2

当您需要为一系列日期生成行时，Numbers表通常很有用。它只是一个包含大量整数的表。您可以阅读有关如何创建一个here（以及其他地方）的信息。完成后，您可以使用这样的查询（这适用于SQL Server）：

;with cteLoan as(
select t1.LoanID, min(t1.Month) StartDate, max(t1.Month) EndDate
from Table1 t1
group by t1.LoanID
)

select c.LoanID, dateadd(month, n.Number, c.StartDate) Month, t2.Rate, null Action
from Numbers n
cross join cteLoan c
join Table2 t2 on t2.Month = dateadd(month, n.Number, c.StartDate)
where n.Number >= 0 and n.number < DATEDIFF(month, c.StartDate, c.EndDate) 

union

select t1.LoanID, t1.Month, t1.Rate, t1.Action
from Table1 t1
order by LoanID, Month

要将结果插入另一个表，您应该能够：

insert into Results(LoadID, Month, Rate, Action)
select c.LoanID, dateadd(month, n.Number, c.StartDate) Month, t2.Rate, null Action
from Numbers n
cross join cteLoan c
join Table2 t2 on t2.Month = dateadd(month, n.Number, c.StartDate)
where n.Number >= 0 and n.number < DATEDIFF(month, c.StartDate, c.EndDate) 

union

select t1.LoanID, t1.Month, t1.Rate, t1.Action
from Table1 t1
order by LoanID, Month

SQL在现有记录之间插入行

2 个答案: