Is an index automatically created when creating a foreign key in PostgreSQL 10?

Question

PostgreSQL

Hello.
Is an index automatically created when creating a foreign key in PostgreSQL 10?
Or does it need to be created manually?

Answer 1

No, it is not created. On the table to which the FK index refers, a unique one must already be created, on the table that refers to the presence of the index is not checked in any way and is not even required. It is only necessary to understand that FK - for each row triggers and without an index there will be N seqscan tables.
Usually the index is created manually. Sometimes intentionally not created.