How can I add a serial number for the following query

How can I add a serial number for the following query. I want final result to be displayed with the serial number.

select
  EP.FirstName
, Ep.LastName
, [dbo].[GetBookingRoleName](ES.UserId,EP.BookingRole) as RoleName
from [3rdi_EventParticipants] as EP
inner join [3rdi_EventSignup] as ES on EP.SignUpId = ES.SignUpId
where EP.EventId =13
and开发者_JS百科 userid in (
select distinct userid from userroles
where roleid not in(19, 20, 21, 22) and roleid not in(1,2))

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Here is the query that tags a serial row number based on the First Name:

SELECT Row_number() OVER(ORDER BY (SELECT 1))  AS 'Row Number', 
       ep.firstname, 
       ep.lastname, 
       [dbo].[Getbookingrolename](es.userid, ep.bookingrole) AS rolename 
FROM   [3rdi_EventParticipants] AS ep 
       INNER JOIN [3rdi_EventSignup] AS es 
         ON ep.signupid = es.signupid 
WHERE  ep.eventid = 13 
       AND userid IN (SELECT DISTINCT userid 
                      FROM   userroles 
                      WHERE  roleid NOT IN( 19, 20, 21, 22 ) 
                             AND roleid NOT IN( 1, 2 )) 

EDIT: Removed the ORDER BY on EP.FirstName, Ep.LastName