Alias by select when multiple selects?

I have an influxdb table called ‘DeviceHeatlh’ with fields fan1rpm, fan2rpm, fan3rpm, fan4rpm.
I’ve added 4 field(fan*rpm) mean () to the select statement and put an alias(Fan1) etc on each.

This gives my a graph with DeviceHealth.Fan3 {host: Device} and similar entries.

I want to do an alias that is $tag_host $select_alias if that makes any sense so the legend for the graph shows “Hostname Fan1” and the RPMs are drawn on the line.

I can’t seem to find the variable to use that alias in the select statement

Any ideas?