how to deal with .com in SQL query?

In the Grocery crud documentation (which is based on Codeigniter) the field ($where) being asked for is:
void set_relation( string $field_name , string  $related_table, string  $related_title_field  [, mixed $where [, string $order_by ] ] )

I have noticed that same syntax "mixed $where" in the codeigniter documentation. What does that mean? Is this not what they are asking for?:
$where=  $where="email=".$this->session->userdata('userid')." AND campaign=".$this->session->userdata('campaign');

proof that an old dog can learn new tricks