Validation class is made by simple for being spare for you, so if you want to add or create a validation ,it is easy to
custormize validation class.
Load Validation
$this->loadHelper('validation');
Number validation
$this->Validation->is_numeric($arr_sql['member_id']));
String & Number validation
$this->Validation->al_numeric($arr_sql['member_id']));
String validation
$this->Validation->alpha($arr_sql['member_id']));
Email validation
$this->Validation->email($arr_sql['member_id']));