I might play with some possibilities, but here's an option that doesn't need concatenation.

IF OBJECT_ID('dbo.SubstringIndex') IS NOT NULL

DROP FUNCTION dbo.SubstringIndex

GO

CREATE FUNCTION dbo.SubstringIndex(

@SourceString varchar(8000),

@delim char(1),

@idx int

)

RETURNS TABLE WITH SCHEMABINDING

RETURN

WITH

E(n) AS(

SELECT n FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0))E(n)

),

E2(n) AS(

SELECT a.n FROM E a, E b

),

E4(n) AS(

SELECT a.n FROM E2 a, E2 b

),

cteTally(n) AS(

SELECT TOP(LEN(@SourceString)) ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) n

FROM E4

),

ctePosition(n) AS(

SELECT TOP( @idx) n

FROM cteTally

WHERE SUBSTRING(@SourceString, n, 1) = @delim

)

SELECT LEFT( @SourceString, MAX(n) - 1) String

FROM ctePosition;

go

declare @SourceStr varchar(8000) = 'www.mytestpage.info',

@delim char(1) = '.',

@idx int = 2;

select * from dbo.SubstringIndex(@SourceStr,@delim,@idx);