- Архив списков рассылки pgsql-interfaces

Hello,
How can one differential between apparently duplicated usernames?
For example I have a postgres id 'www' present within my pg_shadow/pg_user.
I recently installed a package and inadvertantly created another 'www' user.
I have managed to remove the duplicate user by deleting it from pg_shadow by
identifying it via its usesysid field.

How can I

1) Ensure I canot in future create duplicate names?
2) If duplicate users are possible by what other means can the  various instances of them be referenced?

Stephen

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