[GENERAL] foreign keys with constant part

[Marc Mamin]

Hello,

I have to define a foreign relation to something like a unique partial
index.
I could do achieve this  with triggers, but I already have too much of
them, which make the model hard to understand.
for now, I will just add a constant column which allows to define a
standard foreign key.

Would an extension of the foreign keys declaration like following make
sense, or does it too much break SQL standards ?

best regards,

Marc Mamin


create temp table t (
  a int, 
  b int,
  constraint t_pk primary key (a, b)
);
create unique index t_partial on t (a) where b=5;


create temp table f (
 a int
)

alter table f add constraint f_fk  FOREIGN KEY ( a, 5 ) REFERENCES t
(a,b);  --> t_pk
-- or
alter table f add constraint f_fk  FOREIGN KEY ( a ) REFERENCES t (a)
WHERE  t.b=5; --> t_partial


for now:

create temp table f (
 a int,
five  int default 5   -- :-(
)
alter table f add constraint f_fk  FOREIGN KEY ( a, five ) REFERENCES t
(a,b);