references table(multiple columns go here)

Hi folks, 

how do I define a referene from 2 columns in 1 table to 2 columns in another.

I have:

create table ranks (
rid     	int4 default nextval('ranks_rid_seq'::text) unique not null,
rdid		character references depts(did), -- department
rrank		int4 not null,		-- departmental rank
rdesc		character varying(40)	-- Rank Description
);
create unique index "ranks_drank_index" on ranks using btree ("rdid", 
"rrank");

copy "ranks" from stdin;
1	O	1	Trainee TTI
2	O	2	TTI
3	M	1	Cleaner
4	M	2	Passed Cleaner
5	M	3	Fireman.
\.

I would now like to define the following table so that inserts can only happen 
if jdid matches rdid and jrank matches rrank.

create table jobtypes (
jid     	int4 default nextval('jobs_jid_seq'::text) unique not null,
jdid		character references ranks(rdid),	-- This joint reference
jrank		int4 not null references ranks(rrank),	-- needs sorting
jdesc		character varying(40)	-- job description
);

copy "jobtypes" from stdin;
1	M	3	Charge Cleaner
2	O	3	Lock Carriages
\.

(I want the first row to work and the second to be rejected)
-- 
Gary Stainburn
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