SQL遞歸計算的日期

Question

我有一個SQL Server表：

CREATE TABLE [Workflow].[MilestoneDate](
[MilestoneDateId] [int] IDENTITY(1,1) NOT NULL, 
[SpecifiedDate] [datetime] NULL, 
[RelativeDays] [int] NULL, 
[RelativeMilestoneDateId] [int] NULL, 
CONSTRAINT [PK_MilestoneDate] PRIMARY KEY CLUSTERED 
(
[MilestoneDateId] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 
ALTER TABLE [Workflow].[MilestoneDate] WITH CHECK ADD CONSTRAINT [FK_MilestoneDate_MilestoneDate] FOREIGN KEY([RelativeMilestoneDateId]) 
REFERENCES [Workflow].[MilestoneDate] ([MilestoneDateId]) 
GO 
ALTER TABLE [Workflow].[MilestoneDate] CHECK CONSTRAINT [FK_MilestoneDate_MilestoneDate] 

，它有可能像數據：

Id  Date       RelDays RelId 
49  2010-03-04 00:00:00.000  NULL NULL 
746 NULL       6  46 
747 NULL       20  746 
46  2010-02-18 00:00:00.000  NULL NULL 
48  2010-04-04 00:00:00.000  NULL NULL 
47  2010-05-04 00:00:00.000  NULL NULL 
748 NULL       14  48 

我需要能夠做的是讓計算日期如果有一個日期，或者是「父」項的日期（使用RelId）加上RelDays（可以是遞歸的），則該日期是每行的日期。

因此，例如，計算日期ID 747是20天+6天+ 2010-02-18，因此2010-03-16。

Answer 1

試試這個（使用CTE這是隻有SQL Server 2005和高達上可用）：

DECLARE @YourTable table (Id int, Date datetime, RelDays int, RelId int) 
INSERT @YourTable VALUES (49 ,'2010-03-04 00:00:00.000',NULL ,NULL) 
INSERT @YourTable VALUES (746, NULL     ,6 ,46) 
INSERT @YourTable VALUES (747, NULL     ,20 ,746) 
INSERT @YourTable VALUES (46 ,'2010-02-18 00:00:00.000',NULL ,NULL) 
INSERT @YourTable VALUES (48 ,'2010-04-04 00:00:00.000',NULL ,NULL) 
INSERT @YourTable VALUES (47 ,'2010-05-04 00:00:00.000',NULL ,NULL) 
INSERT @YourTable VALUES (748, NULL     ,14 ,48) 

;WITH R AS 
(
    SELECT id,Date,RelDays,RelId --get all parents 
    FROM @YourTable 
    WHERE RelId IS NULL 
    UNION ALL --recursive go through all children, adding the days on 
    SELECT 
     y.id,r.Date+y.RelDays,y.RelDays,y.RelId 
     FROM @YourTable y 
      INNER JOIN R ON y.RelId=r.Id 
) 
select * from R 

OUTPUT：

id   Date     RelDays  RelId 
----------- ----------------------- ----------- ----------- 
49   2010-03-04 00:00:00.000 NULL  NULL 
46   2010-02-18 00:00:00.000 NULL  NULL 
48   2010-04-04 00:00:00.000 NULL  NULL 
47   2010-05-04 00:00:00.000 NULL  NULL 
748   2010-04-18 00:00:00.000 14   48 
746   2010-02-24 00:00:00.000 6   46 
747   2010-03-16 00:00:00.000 20   746 

(7 row(s) affected)