> select * from cpu
name: cpu
time                flag    host    region  value
----                ----    ----    ------  -----
1531922717291594433         serverA us_west 0.64
1531922750165106605 present serverA us_west 0.02
> select mean(value) from cpu group by flag
name: cpu
tags: flag=
time mean
---- ----
0    0.64

name: cpu
tags: flag=present
time mean
---- ----
0    0.02