postgres=# \d pg_stat_activity;
          View "pg_catalog.pg_stat_activity"
    Column     |           Type           | Modifiers
---------------+--------------------------+-----------
 datid         | oid                      |
 datname       | name                     |
 procpid       | integer                  |
 usesysid      | oid                      |
 usename       | name                     |
 current_query | text                     |
 waiting       | boolean                  |
 xact_start    | timestamp with time zone |
 query_start   | timestamp with time zone |
 backend_start | timestamp with time zone |
 client_addr   | inet                     |
 client_port   | integer                  |
View definition:
 SELECT s.datid, d.datname, s.procpid, s.usesysid, u.rolname AS usename, s.curre
nt_query, s.waiting, s.xact_start, s.query_start, s.backend_start, s.client_addr
, s.client_port
   FROM pg_database d, pg_stat_get_activity(NULL::integer) s(datid, procpid, use
sysid, current_query, waiting, xact_start, query_start, backend_start, client_ad
dr, client_port), pg_authid u
  WHERE s.datid = d.oid AND s.usesysid = u.oid;


postgres=# SELECT usename  pg_stat_activity;
ERROR:  column "usename" does not exist
СТРОКА 1:SELECT usename  pg_stat_activity;
             ^
postgres=#