如何使用while循环遍历表并创建具有所需值的另一个表

如何解决如何使用while循环遍历表并创建具有所需值的另一个表

我有两个表：MainTable和MyTable。 MyTable具有唯一的ControlNo和ID。我需要根据EffDate和MainTable从MyTable到ID首先添加ControlNo。

为此，我需要查看PreviousID列，然后查看PreviousID是否在ID列中，依此类推。

所需的输出应如下所示：

---

下面是一个通过提供EffDate值来获取正确的ID的伪数据的示例。它可以工作，但是如何遍历整个MainTable，检索ID和EffDate到单独的表中，然后将该表连接到MyTable？

-- function returns PreviousID based on ID
CREATE FUNCTION [dbo].[GetPriorQuoteID](@ID varchar(50))
RETURNS varchar(50)
AS
BEGIN
    DECLARE @RetVal varchar(50)
    SET @RetVal = NULL
    
    SELECT TOP 1 @RetVal = MainTable.PreviousID
    FROM         MainTable
    WHERE        MainTable.ID = @ID
    
    RETURN @RetVal
END

    -- create sample table
    IF OBJECT_ID('MainTable') IS NOT NULL DROP TABLE MainTable;
    select 3333 as ControlNo,'QuoteID3' as ID,'QuoteID2' as PreviousID,'2020-08-25' as EffDate 
    into MainTable
    union all select 2222 as COntrolNo,'QuoteID2','QuoteID1','2019-08-25'
    union all select 1111 as COntrolNo,NULL,'2018-08-25'
    union all select 7777 as COntrolNo,'QuoteID6','QuoteID5','2020-02-10'
    union all select 6666 as COntrolNo,'2019-02-10'
    select * from MainTable
    
    
    DECLARE @PriorQuote varchar(50)
    DECLARE @RetVal VARCHAR(50) = ''
    DECLARE @ControlNo INT
    DECLARE @ID varchar(50) = 'QuoteID3'
    
    SELECT TOP 1 @ControlNo = MainTable.ControlNo FROM MainTable WHERE MainTable.ID = @ID
    Set @PriorQuote = @ID
    
    SELECT TOP 1 @PriorQuote = MainTable.ID FROM MainTable WHERE MainTable.ControlNo = @ControlNo 
    
    WHILE dbo.GetPriorQuoteID(@PriorQuote) IS NOT NULL AND dbo.GetPriorQuoteID(@PriorQuote)<> @PriorQuote
    BEGIN
            SET @PriorQuote = dbo.GetPriorQuoteID(@PriorQuote)
        END
    
    
    SELECT TOP 1 @RetVal = CONVERT(VARCHAR(10),MainTable.EffDate,101)
    FROM         MainTable
    WHERE        MainTable.ID = @PriorQuote
    SELECT @RetVal
    
    -- clean up
    drop table MainTable
    drop function GetPriorQuoteID

更新：添加虚拟数据表

-- create sample table #MainTable
IF OBJECT_ID('tempdb..#MainTable') IS NOT NULL DROP TABLE #MainTable;
create table #MainTable (ControlNo int,ID varchar(50),PreviousID varchar(50),EffDate date)
insert into #MainTable values
(3333,'QuoteID3','2020-08-25'),(2222,'2019-08-25'),(1111,'2018-08-25'),(7777,'2020-02-10'),(6666,'2019-02-10')
--select * from #MainTable

-- create sample table #MyTable
IF OBJECT_ID('tempdb..#MyTable') IS NOT NULL DROP TABLE #MyTable;
create table #MyTable (ControlNo int,EffDate date)
insert into #MyTable values 
(3333,NULL),NULL)
--select * from #MyTable

解决方法

使用如下所示的CTE，您可以获得预期的结果。 See live demo

详细了解递归CTE here

 ; with cte as 
   (
       select EffDate,ControlNo,ID,Level=1 from MainTable
       where PreviousID is NULL
       union all
       select C.EffDate,M.ControlNo,M.ID,Level=Level+1 from MainTable AS M
       join cte as C on C.ID=M.PreviousID
     )
     
    select MyTable.*,cte.EffDate from cte join MyTable on Mytable.ID=cte.ID

,

您可以使用递归查询遍历层次结构。

我将从将原始表与主表连接开始，这将路径限制为仅对我们感兴趣的行。然后，您可以向父表递归。最后，我们需要对每个路径的父级进行过滤：top()和row_number()对此非常有用。

考虑：

with cte as (
    select t.controlno,t.id,m.previousid,m.effdate,1 lvl 
    from #maintable m
    inner join #mytable t on t.controlno = m.controlno and t.id = m.id
    union all
    select c.controlno,c.id,c.lvl + 1
    from cte c
    inner join #maintable m on m.id = c.previousid
)
select top(1) with ties controlno,id,effdate
from cte 
order by row_number() over(partition by controlno,id order by lvl desc)

Demo on DB Fiddle ：

controlno | id       | effdate   
--------: | :------- | :---------
     3333 | QuoteID3 | 2018-08-25
     7777 | QuoteID6 | 2019-02-10

,

您可以为此使用递归CTE：

WITH cte 
AS
(

SELECT m.ID,m.PreviousID
FROM MainTable m
JOIN MainTable m2
     ON m.previousID = m2.ID
WHERE m2.previousID IS NULL

UNION ALL

SELECT m2.ID,cte.previousID
FROM cte
JOIN MainTable m2
     ON m2.previousID = cte.ID

)

SELECT *
FROM cte;

,

下面是提供的表格的CTE方法的工作示例

;with recur_cte(ControlNo,PreviousID,EffDate,HLevel) as (
    select mt.ControlNo,cast(null as varchar(100)),mt.PreviousID,mt.EffDate,1
    from MainTable mt
    where not exists(select 1 
                     from MainTable mt_in
                     where mt.ID=mt_in.PreviousID)
    union all
    select rc.ControlNo,rc.ID,rc.HLevel+1
    from recur_cte rc
         join MainTable mt on rc.PreviousID=mt.ID and rc.EffDate>mt.EffDate)
select * from recur_cte;

结果

ControlNo   ID  PreviousID  EffDate HLevel
3333    NULL    QuoteID2    2020-08-25  1
7777    NULL    QuoteID5    2020-02-10  1
7777    NULL    NULL        2019-02-10  2
3333    NULL    QuoteID1    2019-08-25  2
3333    NULL    NULL        2018-08-25  3