CREATE OR REPLACE PROCEDURE public.au_upd_сисадмин(_pk_Entity uuid, _hshLogin bytea, _hshPassword bytea) 
AS $$ 
  declare hshLogin_ bytea;
  declare hshPassword_ bytea; 
begin
  SELECT 
    hshLogin_ = hshLogin, 
    hshPassword_ = hshPassword 
  FROM tbl_Пользователи
  WHERE pk_Entity=_pk_Entity;
    
  IF ((hshLogin_ IS NULL) or (hshPassword_ IS NULL)) THEN 
    UPDATE tbl_Пользователи 
    SET hshLogin = _hshLogin, hshPassword=_hshPassword 
    WHERE pk_Entity=_pk_Entity;
end
$$ LANGUAGE sql