Running the following format query returns nothing
SELECT DISTINCT agent_name FROM numerical_metric_data WHERE ts BETWEEN '2018-06-01' AND '2018-06-02' AND frequency = 15000 ORDER BY agent_name DESC
if I change the query and remove the 'AND frequency = 15000' query it returns the data which seems in conflict with the documentation -
"Frequency and ts are essential. Include a number for frequency and a time stamp (that is, 'ts') attribute in every query, as you see in the following examples."
The reason for the no data returned is that the data crosses tier1, the frequency of the data storage changes. So after tier1 data is not stored with a frequency of 15s - default frequency for tier2 and tier3 is 60s and 900s respectively
APM 10.5 and later
Change the frequency qualifier in the query from "=" to ">=" ie..
SELECT DISTINCT agent_name FROM numerical_metric_data WHERE ts BETWEEN '2018-06-01' AND '2018-06-02' AND frequency >= 15000 ORDER BY agent_name DESC