CREATE FUNCTION [dbo].[Fn_StringClean](
                @String varchar(255),
                @Excp varchar(100))
RETURNS varchar(255)
AS
BEGIN
DECLARE @Return varchar(255)

SET @Return = '' 

SELECT @Return = @Return + SUBSTRING(@String,N,1)
FROM Tally
WHERE N <= Len(@String)
      AND SUBSTRING(@String,N,1) LIKE @Excp -- Exceptions
RETURN Ltrim(Rtrim(REPLACE(REPLACE(@Return,'  ',' '),'  ',' '))) -- Remove spaces.
END

GO

select top 1000
Fn_StringClean(CustDetail.last_name + CustDetail.first_name,'[a-z]') 
from customertbl

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[Dbo].[Tally]') AND type in (N'U'))
DROP TABLE [Dbo].[Tally]
GO

/****** Object:  Table [Dbo].[Tally]    Script Date: 08/12/2010 11:49:24 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

--===== Create and populate the Tally table on the fly 

SELECT TOP 11000 --equates to more than 30 years of dates        
IDENTITY(INT,1,1) AS N   
INTO dbo.Tally   
FROM Master.dbo.SysColumns sc1,        
Master.dbo.SysColumns sc2

--===== Add a Primary Key to maximize performance  
ALTER TABLE dbo.Tally    
ADD CONSTRAINT PK_Tally_N         
PRIMARY KEY CLUSTERED (N) 
WITH FILLFACTOR = 100

SELECT TOP 1000 CleanString
FROM customertbl
CROSS APPLY
  (
  SELECT SUBSTRING(last_name + first_name, N, 1)
  FROM Tally
  WHERE N <= LEN(last_name + first_name)
  AND SUBSTRING(last_name + first_name, N, 1) LIKE '[a-z]' FOR XML PATH('')
  ) AS Z (CleanString)