time series - Difference of measurement filtered by tag in InfluxDB -

in influxdb v1.3, have measurement 1 field , tag can take 2 values.

i compute (x mytag=y) - (x mytag=z), using last value of each series when needed (something http://code.kx.com/wiki/reference/aj). in 1 query, if possible.

if above not possible, there different schema (e.g. using separate measurements) feasible? if so, can please elaborate on structure , query?