DECLARE @Dept AS INT
SET @Dept = 40 

SELECT * 
FROM plu_file_dates 
WHERE pluid IN (SELECT pluid 
                FROM plu_file 
                WHERE ToDept = 60 AND FromDept = CASE WHEN @Dept = 0 
                                                      THEN FromDept 
                                                      ELSE @Dept END
				);

DECLARE @Dept AS INT;
SET @Dept = 40;

IF @Dept = 0
BEGIN
    SELECT * 
    FROM plu_file_dates 
    WHERE pluid IN (SELECT pluid 
                    FROM plu_file 
                    WHERE ToDept = 60 
				    );
END
ELSE BEGIN
    SELECT * 
    FROM plu_file_dates 
    WHERE pluid IN (SELECT pluid 
                    FROM plu_file 
                    WHERE ToDept = 60 AND FromDept = @Dept
				    );
END