[SQL] Constraint on 2 column possible?

[Andrei Bintintan]

Hi,   I have a table: CREATE TABLE werke1( id SERIAL, id_hr int4 NOT NULL, id_wk int4 NOT NULL );   CREATE TABLE contact( id SERIAL, type varchar(20), );     Now id_hr and id_wk are all referencing the same table contact(id). In the contact table I have another column called type. How can I write a constraint that checks that id_hr references contact(id) and the contact(type='t1') and that id_wk references contact(id) and the contact(type='t2').   More explicit: the id_hr shows to the id from contact, and this line from contact must have the line type='t1'. The same for id_wk just the type is another.   I can write: CREATE TABLE werke1( id SERIAL, id_hr int4 NOT NULL references contact(id), id_wk int4 NOT NULL references contact(id) ); but how do I check also the type column?   Best regards, Andy.