Add custom info (strings) from mysql query's result to alerts annotations

Basically I have a sensor that is reading the humidity over a big set of materials. (It read one material per 1 or 2 hours)
And I want to send an email alert to know which type of material and batch is the mean value bigger than a certain threshold (that I defined previously).

My datasource is MySql, so I can make a easy query to know which material and batch is giving problems.

I already see this to get the numeric value but I can’t figure it out how do I make to get a string value…