51.71. pg_group
The view pg_group exists for backwards compatibility: it emulates a catalog that existed in PostgreSQL before version 8.1. It shows the names and members of all roles that are marked as not rolcanlogin, which is an approximation to the set of roles that are being used as groups.
Table 51.72. pg_group Columns
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https://www.postgresql.org/docs/12/view-pg-group.html