how to check someones permission on a redhisft external schema
SELECT schemaname, objectname, usename,
has_schema_privilege(usrs.usename, schemaname, 'usage') AS usage
FROM(
SELECT schemaname, tablename AS objectname, schemaname + '.' + tablename AS fullobj
FROM SVV_EXTERNAL_TABLES
) AS objs,(SELECT * FROM pg_user) AS usrs