simple sql query is failing

Thanks. I have it enabled but where is the last query stored?

First, you have to make sure in database config file, you've set save_queries to true.

They are then automatically saved in $this->db.

The sample code should print out most recent query and error message, if it failed on the website. It is of course very rough way to debug code and you shouldn't make that code public, but at least it should get you closer to what's going on with your script on your development environment.