select id, firstname, lastname from users where firstname = 'john' and lastname != '';

select id, firstname, lastname from users where match('@firstname john @lastname !''');

+---------+------------------+----------+
| id      | firstname        | lastname |
+---------+------------------+----------+
|  110809 | John             |          |
|  313681 | John             |          |
|  520045 | John             |          |
|  554136 | John             |          |

select id, firstname, lastname from users where match('@firstname john')