SQL 在现有记录之间插入行

Question

我有一张表，其中包含仅在贷款和偿还的特定日期与贷款相对应的记录 - 即每笔贷款有两条记录。

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

我有另一个记录，每个日期的利率。

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%

我想在贷款表中插入缺失日期的行（以及相应的利率），在给定贷款被取出和偿还之间。鉴于需要为每笔贷款插入中间日期，我无法通过 LEFT JOIN、MERGE 等解决此问题。

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

当您需要为一系列日期生成行时，数字表通常很有用。它只是一个包含大量整数的表。您可以阅读有关如何创建here（以及其他地方）的信息。一旦你有了它，你可以使用这样的查询（这是针对 SQL Server 的）：

;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

Answer 2

您的设计很难，但您没有说明您使用的是什么数据库。这是一个 SQL 服务器示例（查询也适用于 postgreSQL）：

DECLARE @loans TABLE
    (
      LoanID INT ,
      [Month] DATETIME ,
      Rate DECIMAL(4, 2) ,
      [Action] VARCHAR(10)
    );

INSERT  @loans
        ( LoanID, Month, Rate, Action )
VALUES  ( 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 ' );


DECLARE @rates TABLE
    (
      Month DATETIME ,
      Rate DECIMAL(4, 2)
    );
INSERT  @rates
        ( Month, Rate )
VALUES  ( '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 );

WITH    loanStart
          AS ( SELECT   *
               FROM     @loans
               WHERE    Action = 'New'
             ),
        loanEnd
          AS ( SELECT   *
               FROM     @loans
               WHERE    Action = 'Closed'
             ),
        loanRanges ( loanId, lStart, lEnd )
          AS ( SELECT   ls.LoanID ,
                        ls.Month ,
                        le.Month
               FROM     loanStart ls
                        INNER JOIN loanEnd le ON ls.LoanID = le.LoanID
             )
    SELECT  lr.loanId ,
            r.Month ,
            r.Rate ,
            COALESCE(ls.Action, le.Action) AS action
    FROM    @rates r
            INNER JOIN loanRanges lr ON r.Month >= lr.lStart
                                        AND r.Month <= lr.lEnd
            LEFT JOIN loanStart ls ON ls.LoanID = lr.loanId
                                      AND YEAR(ls.Month) = YEAR(r.Month)
                                      AND MONTH(ls.Month) = MONTH(r.Month)
            LEFT JOIN loanEnd le ON le.LoanID = lr.loanId
                                    AND YEAR(le.Month) = YEAR(r.Month)
                                    AND MONTH(le.Month) = MONTH(r.Month)
    ORDER BY lr.loanId ,
            r.Month;