如何通过查询在sql中的日期列中添加循环？

Question

如果ID = 01234并且此 ID 在一个月内进行了 3 次交易，如下所示：

***DAY_no              Balance*** 
   1/1/2018              5000
   10/1/2018             10000
   15/1/2018             12000

我想要这样的数据：

***DAY_no              Balance*** 
   1/1/2018              5000
   2/1/2018              5000
   3/1/2018              5000
   4/1/2018              5000
   5/1/2018              5000
   6/1/2018              5000
   7/1/2018              5000
   8/1/2018              5000
   9/1/2018              5000
   10/1/2018             10000
   11/1/2018             10000
   12/1/2018             10000
   13/1/2018             10000
   14/1/2018             10000
   15/1/2018             12000
   16/1/2018             12000
   17/1/2018             12000
   18/1/2018             12000
   19/1/2018             12000
   20/1/2018             12000
   21/1/2018             12000
   22/1/2018             12000
   23/1/2018             12000
   24/1/2018             12000
   25/1/2018             12000
   26/1/2018             12000
   27/1/2018             12000
   28/1/2018             12000
   29/1/2018             12000
   30/1/2018             12000
   31/1/2018             12000

Answer 1

您可以使用日历表：

CREATE TABLE Calendar(cDate datetime, cDay int, cDayOfWeek int, cDayName varchar(20), cMonth int);

DECLARE @date date = '20180101';
WHILE @date <= '20180131'
BEGIN
    INSERT INTO Calendar VALUES (@date, 
                                 DAY(@date), 
                                 DATEPART(weekday, @date), 
                                 DATENAME(weekday, @date),
                                 MONTH (@date));
    SET @date = DATEADD(day, 1, @date);
END


CREATE TABLE Mov (Day_no date, Balance int);
INSERT INTO Mov VALUES
('20180101', 5000),
('20180110', 10000),
('20180115', 12000);
GO

34 行受影响

SELECT cDAte, (SELECT TOP 1 Balance
               FROM   Mov
               WHERE  Day_no <= cDate
               ORDER BY Day_no DESC) Balance
FROM   Calendar
WHERE cMonth = 1;
GO

日期 | 平衡
:------------------ | ------：
01/01/2018 00:00:00 | 5000
02/01/2018 00:00:00 | 5000
03/01/2018 00:00:00 | 5000
04/01/2018 00:00:00 | 5000
05/01/2018 00:00:00 | 5000
06/01/2018 00:00:00 | 5000
07/01/2018 00:00:00 | 5000
08/01/2018 00:00:00 | 5000
09/01/2018 00:00:00 | 5000
10/01/2018 00:00:00 | 10000
11/01/2018 00:00:00 | 10000
12/01/2018 00:00:00 | 10000
13/01/2018 00:00:00 | 10000
14/01/2018 00:00:00 | 10000
15/01/2018 00:00:00 | 12000
16/01/2018 00:00:00 | 12000
17/01/2018 00:00:00 | 12000
18/01/2018 00:00:00 | 12000
19/01/2018 00:00:00 | 12000
20/01/2018 00:00:00 | 12000
21/01/2018 00:00:00 | 12000
22/01/2018 00:00:00 | 12000
23/01/2018 00:00:00 | 12000
24/01/2018 00:00:00 | 12000
25/01/2018 00:00:00 | 12000
26/01/2018 00:00:00 | 12000
27/01/2018 00:00:00 | 12000
28/01/2018 00:00:00 | 12000
29/01/2018 00:00:00 | 12000
30/01/2018 00:00:00 | 12000
31/01/2018 00:00:00 | 12000

dbfiddle在这里

Answer 2

您应该始终有一个日历表来帮助解决此类问题（并且您应该尽量避免将 SQL Server 中的任何内容视为“循环”——它已针对集合进行了优化）。

-- this produces all the days from 2000-01-01 through 2099-12-31
CREATE TABLE dbo.Calendar(d date PRIMARY KEY);

DECLARE @s date = '20000101', @e date = '20991231';

INSERT dbo.Calendar(d) 
  SELECT DATEADD(DAY, r-1, @s)
  FROM ( SELECT TOP (DATEDIFF(DAY, @s, @e)+1)
           r = ROW_NUMBER() OVER (ORDER BY o.[object_id]) 
         FROM sys.all_objects AS o
         CROSS JOIN sys.all_objects AS c
       ) AS x;

一旦您设置了日历表，就可以轻松地使用查询LEFT JOIN来填补这样的空白。假设您有以下数据：

CREATE TABLE #sample
(
  DAY_no  date, 
  Balance int
);

INSERT #sample(DAY_no,Balance)
VALUES('20180101', 5000 ),
      ('20180110', 10000),
      ('20180115', 12000);

查询是（我什至使用了一个变量来定义您之后的月份）：

DECLARE @month date = DATEFROMPARTS(2018,1,1);

SELECT DAY_no = c.d,
       MAX(s.Balance)
    FROM dbo.Calendar AS c
    LEFT OUTER JOIN #sample AS s
    ON s.DAY_no <= c.d
    WHERE c.d >= @month
      AND c.d <  DATEADD(MONTH, 1, @month)
    GROUP BY c.d
    ORDER BY c.d;

当然，如果您的第一个数据点在本月的第一天之后，您将不得不使查询更加复杂，因为您需要从上个月提取最后一个已知余额。

有关日历表的更多信息，请参阅此提示。