select from InfluxDB where value is null

InfluxDB doesn' understand NULL and will show error if use is null or is not null in the query. In order to find something which is like null we need to look for empty space i.e. use empty single quotes as

SELECT * FROM service_detail where username != ''

You cannot search for nulls in InfluxDB <0.9. You will not be able to insert nulls in Influx >=0.9