I would like to use this class MySqlException in System.Data , but I can not do this because Unity does not have this library natively. I tried adding System.Data in my asset , but this returns me to incompatibility with the native library in System.generic.collections:face_with_spiral_eyes:
Did you try to add the refference to System.Data in current Unity project, I mean References folder in Solution Explorer of VisualStudio?
UPD: For MonoDevelop the same folder located in the Solution tab → ProjectName → Assembly-CSharp → Refenences. As I see in the default counfiguration there is not System.Data lidrary, so you need to add it via right click on Refenences → Edit Refenences…