Search with full name instead of just first name or last name

I am developing an API built with PHP and Codeigniter and I use MySQL as database.

I have a user table called Users which contains the following columns:

- ID
- Firstname
- Lastname
- Email

How can a user search this table using a full name? For example it works fine to search either by Martin or Smith, but not Martin Smith.

This is the query I am using now:

$this->db->select('*');
$this->db->from('users');
$this->db->like('firstname', $args['query']);
$this->db->or_like('lastname', $args['query']);

Update

If I use this query as suggested below I cannot find anything. Not with full name, first name or last name. Then both first name AND last name needs to be the same word.

$this->db->select('*');
$this->db->from('users');
$this->db->like('firstname', $args['query']);
$this->db->like('lastname', $args['query']);

Answer

Straight out of my head, but what about

$input = 'Martin Smith';

$names = explode($input);

$this->db->select('*'); 
$this->db->from('users'); 
$this->db->where_in('firstname', $names); 
$this->db->or_where_in('lastname', $names);

Should output something like:

SELECT * FROM users 
WHERE firstname IN ('Martin', 'Smith') 
OR lastname IN ('Martin', 'Smith')