creating a foreign key referencing a non-primary key

Is there a way to create a foreign key that references a column that's not a primary key of the other table?

(it happens to be part of a composite primary key).

Example:
t1 (id, version, primary_key (id, version)) t2 (t1_id foreign_key on t1(id)) <- not allowed

--
Asya Kamsky

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