在 SQL 服务器上使用 T-SQL 将 CRON 表达式转换为下一个日期时间

Question

我有一列包含 CRON 表达式，表示用户必须执行任务的频率。我想构建一个视图，列出给定用户的日期和要做的事情。但是我需要在 T-SQL 的日期时间计算我的下一个 CRON 出现。如何在 SQL 中解释我的表达式 CRON？

示例：列值 = [0 30 8 1 *?]

我会写： SELECT CrontabSchedule ( '0 30 8 1 *?', GETDATE ()) FROM dbo.UserTasks

有人有解决方案吗？

Answer 1

也许这个链接可以给你一个提示：https://ask.sqlservercentral.com/questions/117285/tsql-sql-function-for-a-cron-expression.html

链接中提供的UDF如下：

CREATE PROCEDURE Q117285.CreateJobScheduleFromCronExpression
     @CronExpression varchar(200)
     , @FieldDelimiterCharacter char(1) -- any whitespace character
 AS
 BEGIN;
     DECLARE @CronExpressionArray TABLE
     (
         Seconds varchar(50)
         , Minutes varchar(50)
         , Hours varchar(50)
         , DayOfMonth varchar(50)
         , Month varchar(50)
         , DayOfWeek varchar(50)
         , Year varchar(50)
     );
     INSERT @CronExpressionArray
         SELECT
               [Seconds]    = [1]
             , [Minutes]    = [2]
             , [Hours]      = [3]
             , [DayOfMonth] = [4]
             , [Month]      = [5]
             , [DayOfWeek]  = [6]
             , [Year]       = [7]
         FROM
         (
             SELECT ds.ItemNumber, ds.Item
             FROM dbo.DelimitedSplit8K(@CronExpression, @FieldDelimiterCharacter) ds
         ) pSrc
         PIVOT
         (
             MAX(pSrc.Item)
             FOR pSrc.ItemNumber IN
                 ([1], [2], [3], [4], [5], [6], [7])
         ) pvt
     ;
     SELECT * FROM @CronExpressionArray;
 END;

DelimitedSplit8K UDF 摘自文章： http: //www.sqlservercentral.com/articles/Tally+Table/72993/

CREATE FUNCTION [dbo].[DelimitedSplit8K]
--===== Define I/O parameters
        (@pString VARCHAR(8000), @pDelimiter CHAR(1))
--WARNING!!! DO NOT USE MAX DATA-TYPES HERE!  IT WILL KILL PERFORMANCE!
RETURNS TABLE WITH SCHEMABINDING AS
 RETURN
--===== "Inline" CTE Driven "Tally Table" produces values from 1 up to 10,000...
     -- enough to cover VARCHAR(8000)
  WITH E1(N) AS (
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
                ),                          --10E+1 or 10 rows
       E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows
       E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max
 cteTally(N) AS (--==== This provides the "base" CTE and limits the number of rows right up front
                     -- for both a performance gain and prevention of accidental "overruns"
                 SELECT TOP (ISNULL(DATALENGTH(@pString),0)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4
                ),
cteStart(N1) AS (--==== This returns N+1 (starting position of each "element" just once for each delimiter)
                 SELECT 1 UNION ALL
                 SELECT t.N+1 FROM cteTally t WHERE SUBSTRING(@pString,t.N,1) = @pDelimiter
                ),
cteLen(N1,L1) AS(--==== Return start and length (for use in substring)
                 SELECT s.N1,
                        ISNULL(NULLIF(CHARINDEX(@pDelimiter,@pString,s.N1),0)-s.N1,8000)
                   FROM cteStart s
                )
--===== Do the actual split. The ISNULL/NULLIF combo handles the length for the final element when no delimiter is found.
 SELECT ItemNumber = ROW_NUMBER() OVER(ORDER BY l.N1),
        Item       = SUBSTRING(@pString, l.N1, l.L1)
   FROM cteLen l
;