Estimados,
el siguiente query recupera el último ingreso de profesores desde la fecha indicada.
select distinct firstname, lastname,FROM_UNIXTIME(u.lastaccess,'%Y-%m-%d') as fecha, q.id,q.shortname as curso
FROM mdl_user u
INNER JOIN mdl_role_assignments ra ON ra.userid = u.id
INNER JOIN mdl_context ct ON ct.id = ra.contextid
INNER JOIN mdl_course q ON q.id = ct.instanceid
INNER JOIN mdl_role r ON r.id = ra.roleid
WHERE r.id = 3
AND FROM_UNIXTIME(u.lastaccess,'%Y-%m-%d') > '2017-06-01'
and ra.roleid = 3
Saludos.