select 'REASSIGN OWNED BY "'||usename||'" TO postgres;' from pg_user order by usename;
select 'DROP OWNED BY "'||usename||'";' from pg_user order by usename;
select 'DROP user "'||usename||'";' from pg_user order by usename;
postgres=# DROP user acc_data;
ERROR: role "acc_data" cannot be dropped because some objects depend on it
DETAIL: privileges for function pg_stat_statements_reset()
1. Before going to solution, list all privileges of a role (grantee)