Return a value if no rows match

Question

The [authorityID] (TinyInt) column will never be null.

What I want is to return a 15 if there are no rows. With the query below I

Answer 1

SELECT  authorityId = isnull(( SELECT   [authorityID]
                               FROM     [docAuthority] WITH ( NOLOCK )
                               WHERE    [grpID] = 0
                                        AND [sID] = 42
                             ), 15)