SQL Select Return Default Value If Null

Two things:

1. Use left outer join instead of inner join to get all the listings, even with missing pictures.

2. Use coalesce to apply the default

   SELECT Listing.Title
       , Listing.MLS
       , Pictures.PictureTH
       , coalesce(Pictures.Picture, 'default.jpg') as Picture
       , Listing.ID  
   FROM Listing 
   LEFT OUTER JOIN Pictures 
       ON Listing.ID = Pictures.ListingID 
   

EDIT To limit to one row:

SELECT Listing.Title
    , Listing.MLS
    , Pictures.PictureTH
    , coalesce(Pictures.Picture, 'default.jpg') as Picture
    , Listing.ID  
FROM Listing 
LEFT OUTER JOIN Pictures 
    ON Listing.ID = Pictures.ListingID 
WHERE Pictures.ID is null
OR Pictures.ID = (SELECT MIN(ID) 
    FROM Pictures 
    WHERE (ListingID = Listing.ID)))