Dla mnie zadziałało to:
SELECT en.enrol, c.summary
FROM mdl_course c
JOIN mdl_enrol en ON en.courseid = c.id
JOIN mdl_user_enrolments ue ON ue.enrolid = en.id
WHERE ue.userid = 'ID USER'
AND en.courseid = 'ID KURSU'
SELECT en.enrol, c.summary
FROM mdl_course c
JOIN mdl_enrol en ON en.courseid = c.id
JOIN mdl_user_enrolments ue ON ue.enrolid = en.id
WHERE ue.userid = 'ID USER'
AND en.courseid = 'ID KURSU'