Consider these two very similar schemas:
Schema 1:
CREATE TABLE foo (
id serial PRIMARY KEY,
frobnitz character(varying 100) NOT NULL UNIQUE
);
CREATE TABLE bar (
id serial PRIMARY KEY,
foo_id int REFERENCES foo(id)
)
Schema 2:
CREATE TABLE foo (
frobnitz character(varying 100) PRIMARY KEY
);
CREATE TABLE bar (
id serial PRIMARY KEY,
frobnitz character(varying 100) REFERENCES foo(frobnitz)
)
The two situations are semantically identical: each record in table bar refers to a record in table foo. The difference is that in the first schema, this referencing is done through an "artificial" serial-integer primary key, while in the second schema this reference is done through a data field that happens to be unique and not null, so it can serve as primary key.
I find Schema 1 awkward and unnatural; more specifically,
foo.id seems unnecessary in light of the non-null uniqueness of foo.frobnitz. But I remember once reading that "long" fields like foo.frobnitz did not make good primary keys.
Is the field
foo.id in Schema 1 superfluous? For example, wouldn't the referencing from bar to foo really be done "behind the scenes" through some hidden field (oid?) instead of through the frobnitz text field? Which of the two schemas would give better perfornance?
Thanks!
kj
