php - Codeigniter gives error: Call to undefined method CI_DB_odbc_driver::get() -

my codeigniter script getting data access database using odbc driver not working when use query builder, it's working when use normal query.

when use query builder this,

$this->db->get('tablename')->result_array(); 

codeigniter gives following error:

fatal error: call undefined method ci_db_odbc_driver::from()

but when use normal query instead of query builder, works perfectly.

$this->db->query('select * tablename')->result_array(); 

i want use query builder. db access db , connection via odbc.

please help.