Show me all "last value" sorted by serial number question from influx newbie

Hello community, I have several electricity meters which write their values into an influx DB. All in one messurement. Now I would like to have the last value for each counter. The meters can be distinguished by their serial number. In Mysql I get the query, somehow I can’t do it with the syntax in influx. Could anyone help me, please

What did you try? what’s your data structure (tags/fields)?

I could generically say that a simple

SELECT last(*) FROM ___ WHERE time > now()-30m GROUP BY *

might do the trick