select to_json(array_agg(row_to_json(r.*) order by r.t)) from (
  select to_char(m.ts::date, 'YYYY/MM/DD') as t,
         trunc(max(m."V1_2" + m."V2_3" + m."V3_1")/300.0,2)::text as vmax,
         trunc(min(m."V1_2" + m."V2_3" + m."V3_1")/300.0,2)::text as vmin
    from metrics m
   where m.machine_id = $1
     and m.ts >= $2
     and m.ts < least($3, $2 + interval '7 days')
group by m.ts::date
) _