在购买记录中，我想从基准日期开始生成+/- 12个月的序列
Client Date
Joe 2020-03-15
Maria 2019-11-01
所以期望的结果将是
Client Date
Joe 2019-03-15
Joe 2019-04-15
.
.
.
Joe 2020-03-15
.
.
.
Joe 2021-02-15
Joe 2021-03-15
Maria 2018-11-01
Maria 2018-12-01
.
.
.
Maria 2019-11-01
.
.
.
Maria 2020-10-01
Maria 2020-11-01
如何实现？
答案 0 :(得分：2)
一个选项使用递归查询：
with cte as (
select client, dateadd(month, -12, date) date, 0 lvl from mytbale
union all
select client, dateadd(month, 1, date), lvl + 1 from cte where lvl < 24
)
select * from cte order by client, date
答案 1 :(得分：2)
另一种选择是与CROSS JOIN配合使用的临时Tally表
示例
Select A.Client
,[Date] = date,DateAdd(MONTH,N,[Date])
From YourTable A
Cross Join ( Select Top (12+1) N=-1+Row_Number() Over (Order By (Select Null)) From master..spt_values n1) B
返回
Client Date
Joe 2020-03-15
Joe 2020-04-15
Joe 2020-05-15
Joe 2020-06-15
Joe 2020-07-15
Joe 2020-08-15
Joe 2020-09-15
Joe 2020-10-15
Joe 2020-11-15
Joe 2020-12-15
Joe 2021-01-15
Joe 2021-02-15
Joe 2021-03-15
Maria 2019-11-01
Maria 2019-12-01
Maria 2020-01-01
Maria 2020-02-01
Maria 2020-03-01
Maria 2020-04-01
Maria 2020-05-01
Maria 2020-06-01
Maria 2020-07-01
Maria 2020-08-01
Maria 2020-09-01
Maria 2020-10-01
Maria 2020-11-01
编辑：如果您希望+/- 12个月，则只需进行少量调整即可
...
Cross Join ( Select Top (24+1) N=-13+Row_Number() Over (Order By (Select Null)) From master..spt_values n1) B
答案 2 :(得分：2)
这是一个略有不同的解决方案，它使用了Tally表的本质。我之所以发布它，是因为他们的DBA不允许很多人使用master数据库中的东西，并且因为需要一系列值是很常见的事情。以下方法也不会在序列的生成中引起逻辑读取。
为了说清楚，“ Tally Table”经常被称为T-SQL的“瑞士军刀”。十分重要的是，十多年前，Erland Sommarskog通过MS“ CONNECT”（“ Feedback”的旧名称）请求了内置的序列发生器。不幸的是，MS除了使请求保持打开状态超过十年之外，什么也没做。
牢记这一点，这是我对Itzik Ben-Gan创建此类功能的出色工作的诠释。它非常有意地只能从“ 0”或“ 1”开始，但可以上升（实际上超过）您可能需要的任何正INT值。如果您需要它以不同于“ 0”或“ 1”的数字开头，则该函数之外的简单整数运算就可以实现。我之所以没有在功能中建立该功能，是因为最常见的用法是从“ 0”或“ 1”开始的序列，而且由于极端的用法，我不想牺牲一两毫秒的性能我把这个功能通过了。
这里是功能……每个人都应该在每个数据库或普通用户可以使用的“实用程序”数据库中拥有类似的东西。
CREATE FUNCTION [dbo].[fnTally]
/**********************************************************************************************************************
Purpose:
Return a column of BIGINTs from @ZeroOrOne up to and including @MaxN with a max value of 10 Quadrillion.
Usage:
--===== Syntax example
SELECT t.N
FROM dbo.fnTally(@ZeroOrOne,@MaxN) t
;
@ZeroOrOne will internally conver to a 1 for any number other than 0 and a 0 for a 0.
@MaxN has an operational domain from 0 to 4,294,967,296. Silent truncation occurs for larger numbers.
Please see the following notes for other important information
Notes:
1. This code works for SQL Server 2008 and up.
2. Based on Itzik Ben-Gan's cascading CTE (cCTE) method for creating a "readless" Tally Table source of BIGINTs.
Refer to the following URL for how it works.
https://www.itprotoday.com/sql-server/virtual-auxiliary-table-numbers
3. To start a sequence at 0, @ZeroOrOne must be 0. Any other value that's convertable to the BIT data-type
will cause the sequence to start at 1.
4. If @ZeroOrOne = 1 and @MaxN = 0, no rows will be returned.
5. If @MaxN is negative or NULL, a "TOP" error will be returned.
6. @MaxN must be a positive number from >= the value of @ZeroOrOne up to and including 4,294,967,296. If a larger
number is used, the function will silently truncate after that max. If you actually need a sequence with that many
or more values, you should consider using a different tool. ;-)
7. There will be a substantial reduction in performance if "N" is sorted in descending order. If a descending sort is
required, use code similar to the following. Performance will decrease by about 27% but it's still very fast
especially compared with just doing a simple descending sort on "N", which is about 20 times slower.
If @ZeroOrOne is a 0, in this case, remove the "+1" from the code.
DECLARE @MaxN BIGINT;
SELECT @MaxN = 1000;
SELECT DescendingN = @MaxN-N+1
FROM dbo.fnTally(1,@MaxN);
8. There is no performance penalty for sorting "N" in ascending order because the output is implicity sorted by
ROW_NUMBER() OVER (ORDER BY (SELECT NULL))
9. This will return 1-10,000,000 to a bit-bucket variable in about 986ms.
This will return 0-10,000,000 to a bit-bucket variable in about 1091ms.
This will return 1-4,294,967,296 to a bit-bucket variable in about 9:12( mi:ss).
Revision History:
Rev 00 - Unknown - Jeff Moden
- Initial creation with error handling for @MaxN.
Rev 01 - 09 Feb 2013 - Jeff Moden
- Modified to start at 0 or 1.
Rev 02 - 16 May 2013 - Jeff Moden
- Removed error handling for @MaxN because of exceptional cases.
Rev 03 - 07 Sep 2013 - Jeff Moden
- Change the max for @MaxN from 10 Billion to 10 Quadrillion to support an experiment.
This will also make it much more difficult for someone to actually get silent truncation in the future.
Rev 04 - 04 Aug 2019 - Jeff Moden
- Enhance performance by making the first CTE provide 256 values instead of 10, which limits the number of
CrossJoins to just 2. Notice that this changes the maximum range of values to "just" 4,294,967,296, which
is the entire range for INT and just happens to be an even power of 256. Because of the use of the VALUES
clause, this code is "only" compatible with SQLServer 2008 and above.
- Update old link from "SQLMag" to "ITPro". Same famous original article, just a different link because they
changed the name of the company (twice, actually).
- Update the flower box notes with the other changes.
**********************************************************************************************************************/
(@ZeroOrOne BIT, @MaxN BIGINT)
RETURNS TABLE WITH SCHEMABINDING AS
RETURN WITH
H2(N) AS ( SELECT 1
FROM (VALUES
(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
,(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
)V(N)) --16^2 or 256 rows
, H4(N) AS (SELECT 1 FROM H2 a, H2 b) --16^4 or 65,536 rows
, H8(N) AS (SELECT 1 FROM H4 a, H4 b) --16^8 or 4,294,967,296 rows
SELECT N = 0 WHERE @ZeroOrOne = 0 UNION ALL
SELECT TOP(@MaxN)
N = ROW_NUMBER() OVER (ORDER BY N)
FROM H8
;
p.s。我通常不对对象使用“匈牙利符号”，但是我也有一个提示表，并且不能有两个名称相同的对象。
一旦有了类似的东西，需要数字序列的问题就变得容易，快速且廉价。例如，这是我使用此功能编写解决OP问题解决方案的方法。
--===== Solve the problem using the fnTally function as a numeric sequence generator starting
-- at 0 and ending at the +/- 12 month differences for each Client's base date.
DECLARE @OffsetMonths INT = 12 --Just to make it a bit more flexible
;
SELECT d.Client
,[Date] = DATEADD(mm,t.N-@OffsetMonths,d.[Date])
FROM #TestTable d
CROSS APPLY dbo.fnTally(0,@OffsetMonths*2) t
ORDER BY d.Client,[Date]
;
如果您要测试该代码，这就是我为测试表构建的代码。
--===== Create and populate a test table.
-- This is NOT a part of the solution.
-- We're just creating test data here.
DROP TABLE IF EXISTS #TestTable
;
CREATE TABLE #TestTable
(
Client VARCHAR(20)
,[Date] DATE
)
;
INSERT INTO #TestTable
(Client,[Date])
VALUES ('Joe','2020-03-15')
,('Maria','2019-11-01')
;
如果您想了解更多有关“理货表格”和相关功能如何工作的信息，请点击此处，链接到我的文章，该文章的发布时间太长了。
The "Numbers" or "Tally" Table: What it is and how it replaces a loop