Database Query Filter

Is there any way to filter final query. I want to filter some keyword. like
 UNION
 CAST
 Information_scheme

I don't want to allow these keywords in the query either plain query or using active record. How can I filter these keyword without any modification in system folder.

Please advice me.

You can use $this->db->get_compiled_select() to get the final query and filter it, then use $this->db->query($filtered_query) to run it.
Read more http://localhost:8080/ci/public/user_gui...led_select