Under Codeigniter, is it possible to see mysql_error()?

Yes, this is the mysql_error() wrapper.

$this->db->_error_message();

And the mysql_errno wrapper is:

$this->db->_error_number();

mysql codeigniter transactions

You may be able to use call_function in the db class to access mysql_error:

Of course, you could also just turn on the debug flag in the DB config, to tell CI to display db errors:

db_debug - TRUE/FALSE (boolean) - Whether database errors should be displayed.

CodeHunter