Conditional PostgreSQL foreign key -


is possible in postgresql conditionally add foreign key?

something like:alter table table1 add foreign key (some_id) references other_table some_id not in (0,-1) , some_id not null;

specifically, reference table has positive integers (1+) table need add foreign key can contain 0 (0), null , negative 1 (-1) instead, meaning different.

notes:

i aware poor table design, clever trick built 10+ years ago when features , resources have available @ point did not exist. system running hundreds of retail stores going , changing method @ point take months don't have.

i can not use trigger, this must done foreign key.

you can add "shadow" column table1 holds cleaned values (i.e. 0 , -1). use column referential integrity checks. shadow column updated/filled simple trigger on table1 writes values 0 , -1 shadow column. both 0 , -1 mapped null.

then have reference integrity , unchanged original column. downside: have little trigger , redundant data. alas, fate of legacy schema!


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