The insert() sub is done! (but not fully tested :( )
Simplifying the insertion : it gives back the id so I don't have to send
a supplementary query.
Some statements are prepared but not useful right now.
Every query is handled in a "eval" bloc. No exception may be raised.

TODO: maybe the statements will be object attributes because they don't
change for this part.
TODO: define something to return if needed.