sql help

["Smith, Mike" <Mike_Smith@xxxxxxxxxxxxxxxx>]

I have a file that has  a contract#, a flag that indicates if the file
is a master contract, and a master contract#
so i might have something like 
 
contract    flag    master
1                y
2                y
3                n        1
4                n        2
5                n        1
 
 
where contract 1 is a master contract with subordinate contracts 3 and 5
 
i'm trying to create an SQL statement that will list the master
contracts and the subordinate contracts. So far i haven't been able to
get this to work.  Can i do this in 1 statement. 
 
i want results such as 
 
 
contract    flag    master
1                y
3                n        1
5                n        1
2                y        
4                n        2