composite foreign key relationship

Follow this example

if object_id('DET','U') is not null drop table DET
if object_id('TST','U') is not null drop table TST
go
create table TST (numrif int not null, datrif date not null)
alter table TST add constraint PK_TST primary key (numrif, datrif)

create table DET (numrif int not null, datrif date not null, numdet int not null)
alter table DET add constraint PK_DET primary key (numrif, datrif, numdet)

alter table DET add constraint FK_DET_TST foreign key (numrif, datrif) 
                               references TST(numrif, datrif)

--insert some data into TST
insert into TST select 1, '1 Jan 2012'
insert into TST select 2, '1 Feb 2012'
insert into TST select 3, '1 Mar 2012'

--insert some data into DET, enforcing the FK
insert into DET select 1, '1 Jan 2012', 10
insert into DET select 1, '1 Jan 2012', 20
insert into DET select 2, '1 Feb 2012', 100

--this will fail the FK
insert into DET select 3, '1 Feb 2012', 999