select based on multi-column primary keys - Mailing list pgsql-sql

I have set up a table with a multi-column primary key constraint:

CREATE TABLE iopoints
( enclosureid numeric(3) NOT NULL, pointid char(4) NOT NULL, equipmentgroup varchar(64) NOT NULL, deviceid varchar(8),
devicetypevarchar(24), operationdesc varchar(64) NOT NULL, entrytime timestamp NOT NULL DEFAULT
('now'::text)::timestamp(6)with 
 
time zone, systemid numeric(3) NOT NULL, CONSTRAINT "ID" PRIMARY KEY (systemid, enclosureid, pointid)
)
WITHOUT OIDS;

If I had a row in the table where systemid=123, enclosureid=ab, 
pointid=56, I would have a Primary Key ("ID") of 123ab56 for that row.

I now want to run a select based on the Primary Key, something like:

SELECT * FROM iopoints WHERE ID = 123ab56

Is something like this even possible?  Or am I forced to do:

SELECT * FROM iopoints WHERE systemid=123 AND enclosureid=ab AND pointid=56

I have searched high and low but can not find a syntax example of how to 
select based on a multi-column primary key, any tips?

Thanks,

mawrya