SQL Server string substring with d iterations - sql-server

Question

I have a string:
#TempCol = sigma_x1,sigma_x2,...,sigma_xd,XX,YY,ZZ
I want to get a substring to get the string sigma_x1,sigma_x2,...,sigma_xd.
d is a variable, so it can be 1, 3, 20, ..., etc.
I know the value of d, but what I don't know is how to get the substring of the original string with d terms.
I tried this:
#L = ''
SET #ColumnNo = 0
WHILE #ColumnNo <= #d
BEGIN
SET #L = #L + ' ' + SUBSTRING(#TempCol, 1, CHARINDEX(',',#TempCol)-1 )
SET #TempCol = REPLACE ( #TempCol, LTRIM(RTRIM(#L) ) ,'')
Set #ColumnNo = #ColumnNo + 1
PRINT #L
END
but I do not know how to get the expected result.

Answer 1

DECLARE #TempCol varchar(max), #d int, #p int, #Result varchar(max);
SET #TempCol = 'item1,item2,itemA,itemB,item#,item$';
SET #d = 3;
SET #p = 1;
WHILE #d > 0 AND #p > 0 BEGIN
SET #p = CHARINDEX(',', #TempCol, #p);
IF #p > 0 SET #p = #p + 1;
SET #d = #d - 1;
END;
IF #p = 0
SET #Result = #TempCol
ELSE
SET #Result = SUBSTRING(#TempCol, 1, #p - 2);
SELECT #Result;
Basically, the loop just searches for the final position to cut at. The substring is extracted after the loop.
If you specify too large #d then the result will simply be all of #TempCol, otherwise you get the desired number of items.

Answer 2

What you need is a split function (shown at the bottom).
With SplitItems As
(
Select Position, Value
, Row_Number() Over ( Order By Position ) As ItemNum
From dbo.udf_Split( #TempCol, ',' )
)
Select Value
From SplitItems
Where ItemNum <= #d
If you want the assembled string up to a given point you would simply do:
With SplitItems As
(
Select Position, Value
, Row_Number() Over ( Order By Position ) As ItemNum
From dbo.udf_Split( #TempCol, ',' )
)
Select ',' + Value
From SplitItems
Where ItemNum <= #d
Order By ItemNum
For Xml Path('')
Split function:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
Create FUNCTION [dbo].[udf_Split]
(
#DelimitedList nvarchar(max)
, #Delimiter nvarchar(2) = ','
)
RETURNS TABLE
AS
RETURN
(
With CorrectedList As
(
Select Case When Left(#DelimitedList, Len(#Delimiter)) <> #Delimiter Then #Delimiter Else '' End
+ #DelimitedList
+ Case When Right(#DelimitedList, Len(#Delimiter)) <> #Delimiter Then #Delimiter Else '' End
As List
, Len(#Delimiter) As DelimiterLen
)
, Numbers As
(
Select TOP( Coalesce(DataLength(#DelimitedList)/2,0) ) Row_Number() Over ( Order By c1.object_id ) As Value
From sys.columns As c1
Cross Join sys.columns As c2
)
Select CharIndex(#Delimiter, CL.list, N.Value) + CL.DelimiterLen As Position
, Substring (
CL.List
, CharIndex(#Delimiter, CL.list, N.Value) + CL.DelimiterLen
, CharIndex(#Delimiter, CL.list, N.Value + 1)
- ( CharIndex(#Delimiter, CL.list, N.Value) + CL.DelimiterLen )
) As Value
From CorrectedList As CL
Cross Join Numbers As N
Where N.Value <= DataLength(CL.List) / 2
And Substring(CL.List, N.Value, CL.DelimiterLen) = #Delimiter
)