Querystring for Pulling data Into Webservice

Hi Guys I have a webservice using the following query it works absolutly
fine 

new iDB2Command("Select * from ctx4nthg where REF = '123456'"
,connDB2);

This works fine but I want it to return different results depending on
the value of something called filter

i have tried 
new iDB2Command("Select * from ctx4nthg where REF =" + @filter
,connDB2);
and 
new iDB2Command("Select * from ctx4nthg where REF =@filter" ,connDB2);
can anyone give me some tips

Rohan



______________________________________________________________________________
This message has been checked for viruses by Corpex
using the ArmourPlate Virus Scanning Service. To find out
how to protect your company visit http://www.armourplate.com
or call Corpex on +44 (0)207 430 8000.