Retrieve data from two tables where table 2 has multiple entries for one value
Provided customer_users has ID and the order needed is customers.customerid , customer_users.ID you may ask sql server to show NULL in all but first row in a partition. Adjust ordering as needed.

SELECT '' AS campaigndaysremaining, COUNT(*) OVER () AS totalrecordcount, *,
  [show CustomerId]=CASE ROW_NUMBER() OVER (PARTITION BY C.customerid ORDER BY CU.ID) WHEN 1 THEN C.customerid END
FROM customers C 
LEFT OUTER JOIN customer_users CU ON C.customerid = CU.customerid 
WHERE C.customerid &gt; 0
ORDER BY C.customerid , CU.ID


Getting only one user is a bit different task. First option is OUTER APPLY to get this only user 

SELECT '' as campaigndaysremaining, * 
FROM customers C 
OUTER APPLY (
  SELECT TOP(1) cu.userid, cu.request, cu.regionid, cu.primaryrep, cu.dateadded ,
     COUNT(*) OVER () AS totalrecordcount
  FROM customer_users CU 
  WHERE C.customerid = CU.customerid 
  ORDER BY cu.userid -- change ordering as needed
) CU
WHERE C.customerid &gt; 0 AND (C.company like '%blue%' OR c.altcompanyname like '%blue%') AND status = 0 
ORDER BY C.company ASC