Select duplicated values

Lets say that the primary key column is A.  I am trying to select all
the rows with duplicated values in columns B, C, and D.

I am not too experienced in SQL syntax, and I've used the following:
select A from table_name where B+C+D in (select B+C+D from table_name
group by B+C+D having count(*)>1  )

I'm looking for a better way, since I am just adding the three columns
together right now.

Jeffrey