customer function vertica

Hello! I began to study vertiсa. I tryis created customer function but getting error. Help me pliase
My code sql
create or REPLACE FUNCTION itog_report_status.get_warn_lvl(day_count NUMERIC)
returns varchar
AS $function$
DECLARE res varchar ;
BEGIN
select status::varchar
from itog_reports_status.status_warn_level
where days = (
select MIN(days)
from itog_reports_status.status_warn_level
where day_count <= days);
RETURN COALESCE(res, 'RED')
END;