Thanks for your answer.
No, I don't have any other code like "insert" at the moment, because the table I tried to create is never created, so I'm basically stuck at this point. As mentioned, I get the error : number of '?'s in statement string does not match argument count when I try to create the table. (The (error) callback is called).
I'm using Chrome, and when I inspect "WebSQL" under the "Resources" tab, I only have a table "kv" created (which I assume is used to store as data "key-value", and not using the query method. No sign of my "categories" table.