Return InfluxDB results where field key has a value

1

I wish to query a measurement and return results where specified field keys have values.

SELECT * FROM L2
WHERE time<='2018-06-16T12:00:00Z' AND time>='2018-10-14T12:00:00Z'
AND ("P16" =~ /./ OR "P17" =~ /./ OR "P18" =~ /./)

My measurement has about 60 field keys:

> show field keys from L2
name: L2
fieldKey fieldType
-------- ---------
P110     float
P111     float
P16      float
P17      float
P18      float
P31      float
...
P95      float
P98      float

I next verify that my measurement has data:

> SELECT P16, P17, P18 FROM L2 WHERE time>='2018-06-13T12:00:00Z' AND time<='2018-06-13T12:10:00Z'
name: L2
time                P16     P17    P18
----                ---     ---    ---
1528891321000000000 77496.5
1528891322000000000         111810 44267.9
1528891501000000000 77496.8
1528891502000000000         111810 44267.9
1528891681000000000 77497.1
1528891682000000000         111810 44267.9
>

After consulting the documentation as well as various posts on this site, I give it a try:

> SELECT P16, P17, P18 FROM L2 WHERE "P17" =~/./
> SELECT P16, P17, P18 FROM L2 WHERE "P17" =~/.*/
> SELECT P16, P17, P18 FROM L2 WHERE "P17" !=''
> SELECT P16, P17, P18 FROM L2 WHERE "P17" !=""
> SELECT P16, P17, P18 FROM L2 WHERE P17 != null
>

Why are results not returned? Thanks!