Codeigniter query to search for any word in user-supplied phrase

I have written some code to make a search in the CodIgniter3 framework. When I insert 2 or more words to search input, it works great, however, when I enter just 1 word, it gives this error.

How can I solve this problem? Here is my controller:

function search() {
    $keyword = strip_tags($this->input->get('searchforcourses'));
    $keyword = explode(" ", $keyword);

    $data['title'] = 'Bütün Kurslar Burada';
    $data['courses'] = $this->courses_model->courses_search($keyword);

    $this->load->view('templates/header');
    $this->load->view('courses/courses', $data);
    $this->load->view('templates/footer');
}

And here is my model:

function courses_search($keyword) {
    $this->db->select('*');
    $this->db->from('courses');
    $this->db->like('title',$keyword[0]);
    $this->db->or_like('title',$keyword[1]);
    $this->db->join('instructors', 'instructors.id = courses.instructor_id', 'left');
    $this->db->join('categories', 'categories.id = courses.category_id', 'left');
    $query = $this->db->get();
    return $query->result_array();
}

The error means you are trying to access an unexisting key 1, your code is wrong on the model level, your code is only getting two keywords, what if the user searched for three keywords? are you just going to ignore them?

I suggest doing it like this:

function courses_search($keyword) {
    $this->db->select('*');
    $this->db->from('courses');
    // You should consider limiting the number of keywords to avoid long loops
    // Limits to 20 keywords
    $keyword = array_slice($keyword, 0, 19);
    // You can also limit it in the 3rd parameter of the explode function
    // Loop through the keywords
    forearch($keyword as $key){
        $this->db->or_like('title',$key);
    }
    $this->db->join('instructors', 'instructors.id = courses.instructor_id', 'left');
    $this->db->join('categories', 'categories.id = courses.category_id', 'left');
    $query = $this->db->get();
    return $query->result_array();
}