On 22.06.18 00:35, PG Doc comments form wrote:
> because 0::OID does not reference a valid pg_collation.oid.
>
> In the IRC, Zr40 helpfully pointed out that the latest documentation readily
> clarifies: "For each column in the index key, this contains the OID of the
> collation to use for the index, or zero if the column is not of a collatable
> data type."
It's a standard convention in the PostgreSQL system catalogs that OID
zero means "none". There are likely many places where this is not
explicitly documented.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services