# Math operations between fields **URL:** \ **Category:** Telegraf\ **Tags:** influxdb\ **Created:** [May 12, 2017, 1:14pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912 "2017-05-12T13:14:12Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Silva](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@Silva](https://community.influxdata.com/u/Silva)\ **Post date:** [May 12, 2017, 1:14pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/1 "2017-05-12T13:14:13Z")
Hello, I posted this in Stackoverflow ([https://stackoverflow.com/questions/43902592/math-operations-between-measurements](https://stackoverflow.com/questions/43902592/math-operations-between-measurements)) because I didn’t knew this forum. This is the issue. I’m sending measurements to InfluxDB using Telegraf, but I have troubles trying to do math operations between different fields. For example, I have a data set like this: ``` SELECT * FROM "Storage" WHERE hostname = 'agent01' time Device StorageAllocationUnit StorageUsed TotalSize agent_host host hostname ---- ----------- --------------------- ----------- --------- ---------- ---- -------- 1494279001000000000 Virtual memory 1024 385169092 400171824 agent01 host1 agent01 1494279001000000000 Swap space 1024 144 4194300 agent01 host1 agent01 1494279001000000000 Shared memory 1024 2830276 2830276 agent01 host1 agent01 1494279001000000000 Physical memory 1024 385168948 395977524 agent01 host1 agent01 1494279001000000000 Memory buffers 1024 3973996 395977524 agent01 host1 agent01 1494279001000000000 Cached memory 1024 306704448 306704448 agent01 host1 agent01 ``` I want to calculate the used Memory with this formula: ``` Physical memory = StorageUsed*StorageAllocationUnit where Device = 'Physical memory' Cached memory = StorageUsed*StorageAllocationUnit where Device = 'Cached memory' ... Used Memory = Physical memory - Cached memory - Memory buffers - Shared memory ``` It is possible to do math operations between fields? all of them are in the same measurement. I’m using InfluxDB 1.2.2. ---
**Author:** ![jackzampolin](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/jackzampolin/32/5_2.png) [@jackzampolin](https://community.influxdata.com/u/jackzampolin)\ **Post date:** [May 15, 2017, 4:49pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/2 "2017-05-15T16:49:39Z")
@Silva Each of what you are calling “measurements” are actually being stored as [`fields`](https://docs.influxdata.com/influxdb/v1.2/concepts/glossary/#field) in influx. Also what you are calling a “series” is actually a [`measurement`](https://docs.influxdata.com/influxdb/v1.2/concepts/glossary/#measurement) in influx. Math between `fields` in a `measurement` is supported in InfluxDB. Can you share the queries that you have tried? ---
**Author:** ![Silva](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@Silva](https://community.influxdata.com/u/Silva)\ **Post date:** [May 16, 2017, 6:34pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/3 "2017-05-16T18:34:10Z")
I updated the post with the changes that you told me. I tried using JOINs but Influx don’t support that command, and I don’t know other way to do it. I have to substact the outcome of these 2 queries: ``` SELECT StorageUsed*StorageAllocationUnit FROM "Storage" WHERE hostname = 'agent01' where "Device" = 'Physical memory'; SELECT StorageUsed*StorageAllocationUnit FROM "Storage" WHERE hostname = 'agent01' where "Device" = 'Cached memory'; ``` Like this: ``` SELECT (SELECT StorageUsed*StorageAllocationUnit from "Storage" where "hostname" = 'agent01' and "Device" = 'Cached memory') - (SELECT StorageUsed*StorageAllocationUnit from "Storage" where "hostname" = 'agent01' and "Device" = 'Physical memory') as Difference ``` ---
**Author:** ![oliver](https://avatars.discourse-cdn.com/v4/letter/o/85f322/32.png) [@oliver](https://community.influxdata.com/u/oliver)\ **Post date:** [May 17, 2017, 1:54pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/4 "2017-05-17T13:54:20Z")
> [@jackzampolin](#): > > between fields in a measurement is supported in InfluxDB. Can you share the queries that you have tried? Looking for the same - one measurement math between 2 fields (both calculated by non\_neg\_derivative). SELECT “compress” FROM (SELECT (non\_negative\_derivative(mean(“bytes\_recv”), 1s) \*8 WHERE “interface” = ‘eth1’) - (non\_negative\_derivative(mean(“bytes\_sent”), 1s)\*8 WHERE “interface” = ‘eth2’) as “compress” FROM “net” WHERE “host” = ‘ovpn1’ AND $timefilter GROUP BY time($interval)) ---
**Author:** ![oliver](https://avatars.discourse-cdn.com/v4/letter/o/85f322/32.png) [@oliver](https://community.influxdata.com/u/oliver)\ **Post date:** [May 19, 2017, 12:47pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/5 "2017-05-19T12:47:07Z")
Any ideas regarding my request? Many Thanks in advance! ---
**Author:** ![aurimasplu](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@aurimasplu](https://community.influxdata.com/u/aurimasplu)\ **Post date:** [June 15, 2018, 12:07pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/6 "2018-06-15T12:07:54Z")
I have exactly same problem. I need some kind of way to do math between fields. I use telegraf to collect CPU and memory data from various types of devices via SNMP. I have no problem writing data to InfluxDB and Elasticserch and later I use queries to calculate percents. But problem is that various device report these types of metrics differently. Some report used memory + free memory, some used memory + all memory and etc. So I end up having to put up to 10 different queries in Grafana just to make universal dashboard for memory. ---
**Author:** ![raja\_kernel](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/raja_kernel/32/3149_2.png) [@raja\_kernel](https://community.influxdata.com/u/raja_kernel)\ **Post date:** [June 11, 2019, 2:30pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/7 "2019-06-11T14:30:46Z")
Hi , I am also trying in similar kind of Quires , My intention is to Calculate “Physical Memory excluding Buffer ,Cache and Shared memories” from SNMP Data. can any one help us on this ?? I gone through “[Cannot compute math on result of two subqueries · Issue #9779 · influxdata/influxdb · GitHub](https://github.com/influxdata/influxdb/issues/9779)” closed in 2018 , is computation on sub query elements issue, still persists ? or is there any work around for this ?? ---
**Author:** ![nated099](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/nated099/32/3571_2.png) [@nated099](https://community.influxdata.com/u/nated099)\ **Post date:** [September 20, 2019, 2:22pm UTC](https://community.influxdata.com/t/math-operations-between-fields/912/8 "2019-09-20T14:22:47Z")
Hello. From what I’ve attempted it seems you must include a function for each field. Lets say you want to subtract the sum of two fields, fieldA and fieldB. To do this you must use the functions as follows: `SELECT sum("fieldA") - sum("fieldB")` An incorrect way of attempting this would be: `SELECT sum("fieldA"-"fieldB")` Hope this helps anyone who stumbles on this thread. I know it’s a little late for OP and others.