General developer forum

Perhaps something like this?

SELECT l.userid,
       COUNT(l.userid) AS nrlogins 
  FROM mdl_log l
 WHERE l.module = 'user'
       AND
       l.action = 'login'
       AND
       l.time BETWEEN UNIX_TIMESTAMP('2013-01-01 00:00:00') AND UNIX_TIMESTAMP('2014-12-31 23:59:59')
 GROUP BY l.userid