Error 1096 - No Tables Used - CodeIgniter

Question

I am trying to use one of stores hooks to insert data into the database when displaying the success page after paying online for an order and I get the following error:

Error Number: 1096
No tables used
SELECT *

This is the function I am calling on the store_order_complete_end hook from store:

public function store_order_complete_end($member_id) { // hook
    try {
        // generate coupon code
        $coupon_code = 'FLK-' . mt_rand(100000000, 999999999);

        // generate coupon code until code is unique
        while ($this->check_coupon($coupon_code)) {
            $coupon_code = 'FLK-' . mt_rand(100000000, 999999999);
        }

        //-----------------------------------------------------
        // -- inserting into table exp_channel_titles --
        // retrieving the next available primary key value
        $entry_id = ee()->db->insert_id();

        // array containing the data that will be inserted into the database
        $titles = array(
            'entry_id' => $entry_id,
            'site_id' => 1,
            'channel_id' => 8,
            'author_id' => $member_id,
            'ip_address' => null,
            'title' => $coupon_code,
            'url_title' => strtolower($coupon_code),
            'status' => 'open',
            'entry_date' => strtotime('now')
        );

        // insert coupon into table exp_channel_titles
        ee()->db->insert('exp_channel_titles', $titles);
        //-----------------------------------------------------

        //-----------------------------------------------------
        // -- inserting into table exp_channel_data --
        // array containing the data that will be inserted into the database
        $data = array(
            'entry_id' => $entry_id,
            'site_id' => 1,
            'channel_id' => 8,
            //'field_id_44' => $assoc_product,
            'field_id_45' => $member_id
        );

        // insert coupon into table exp_channel_data
        ee()->db->insert('exp_channel_data', $data);
        //-----------------------------------------------------
        /// setting the return value if successful
        $this->returndata = true;

        // returning the data
        return $this->returndata;
    } catch (Exception $err) {
        // returning the exception if any
        return $err;
    }
}

Referenced function:

public function check_coupon($coupon_code) {
    try {
        // selecting the coupon code field
        ee()->db->select('title');

        // building the conditions
        $query = ee()->db->get_where('exp_channel_titles', array('title' => $coupon_code, 'channel_id' => 8));

        // retrieving the data into a variable
        $result = $this->EE->db->get()->result_array();

        // return true if the coupon exist
        if (!empty($result)) {
            return true;
        }

        // return false if the coupon does not exist
        return false;
    } catch (Exception $err) {
        // returning the exception if any
        return $err;
    }
}

Answer 1

Try changing this line:

$query = ee()->db->get_where('exp_channel_titles', array('title' => $coupon_code, 'channel_id' => 8));

To this:

ee()->db->where('exp_channel_titles', array('title' => $coupon_code, 'channel_id' => 8));