I don't even think it's ready to be used in a prototype. No joins, no unions, as mentionned before SQL injections. I mean, besides teaching yourself what a basic Mapper is, I don't see any use to this.
Not just teaching myself. This could teach anyone else that didn't know about object mappers. Even if this is the most insecure code in the world, it can be improved. That's the reason it is on github. You could contribute and add joins, unions, sanitize the user inputs, etc.