Codeigniter Check For Duplicate on Edit Function

public function checkDuplicateEmail($post_email) {

    $this->db->where('email_id', $email_id);

    $query = $this->db->get('my_registration_table');

    $count_row = $query->num_rows();

    if ($count_row > 0) {
      //if count row return any row; that means you have already this email address in the database. so you must set false in this sense.
        return FALSE; // here I change TRUE to false.
     } else {
      // doesn't return any row means database doesn't have this email
        return TRUE; // And here false to TRUE
     }
}

<?php
    if(isset($_POST['is_default'])){
    echo "checked"; set_checkbox('is_default', '1');
    }elseif ($customer_group[0]['is_default'] == "1"){
    echo "checked"; set_checkbox('is_default', '1');
    }
 ?>

SELECT * FROM posts GROUP BY forumId;

SELECT * 
FROM (
SELECT * 
    FROM posts
    ORDER BY date DESC
    LIMIT 18446744073709551615
) AS sub
GROUP BY sub.forumId
ORDER BY id DESC

$this->userdb->UsernameDuplicatechecking($userName,$id);

$this->db->where("userId <> $id");

SELECT Email FROM Persona WHERE Email = @Email AND Id != @Id