Mathematics across measurements

Apologies if this is a duplicate, I had a look and couldn't see a relevant issue. I can see from the documentation how to select from multiple measurements (although it calls them series, still, at https://influxdb.com/docs/v0.9/query_language/data_exploration.html ) For example, with data inserted by telegraf, you can do: `select * from disk_used,disk_total where host = 'myhostname' and path = '/'` How would you express that as a percentage? I've tried variations of the following, and none seem to work: `select disk_used.value/disk_total.value from disk_used, disk_total where host = 'myhostname' and path='/'` The "mydb"."retentionpolicy"."measurement" syntax doesn't work there, either. Is it a good idea to add aggregation functions for cases like `diff(value1, value2) from m1, m2` and `divide(value, value) from m1, m2`, or should the arithmetic operators be working? Also, I noticed when experimenting that it's also not possible to divide one derivative by another. For example, if I have two counters, bytes transferred and api calls made - both of which are constantly going up - how would you calculate the mean bytes per api call?

Posted by srfraser on Aug 4, 2015, 7:02 PM

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