Mysql left join 4 possible values - mysql

Question

we're running this query in moodle database:
SELECT l.*,
MAX(l.time) as time,cat.id as catid, cat.name as catname,c.id as courseid,
c.fullname as coursename,
m.name as module,
r.revision as revision,
r.name as resourcename,
sco.name as scormname,
glo.name as glossaryname,
qui.name as quizname
FROM {log} l
INNER JOIN {user} u ON l.userid = u.id
INNER JOIN {course} c ON l.course = c.id
INNER JOIN {course_categories} cat ON c.category = cat.id
INNER JOIN {course_modules} cm ON l.cmid = cm.id
INNER JOIN {modules} m ON cm.module = m.id
LEFT JOIN {resource} r ON cm.instance = r.id and l.module = "resource"
LEFT JOIN {scorm} sco ON cm.instance = sco.id and l.module = "scorm"
LEFT JOIN {glossary} glo ON cm.instance = glo.id and l.module = "glossary"
LEFT JOIN {quiz} qui ON cm.instance = qui.id and l.module = "quiz"
WHERE LOWER(l.action) LIKE LOWER(:modaction) COLLATE utf8_bin AND l.userid = :userid
GROUP BY l.cmid
ORDER BY MAX(l.time) DESC
and i would like something like this:
SELECT l.*,
MAX(l.time) as time,cat.id as catid, cat.name as catname,c.id as courseid,
c.fullname as coursename,
m.name as module,
r.revision as revision,
r.name as resourcename
FROM {log} l
INNER JOIN {user} u ON l.userid = u.id
INNER JOIN {course} c ON l.course = c.id
INNER JOIN {course_categories} cat ON c.category = cat.id
INNER JOIN {course_modules} cm ON l.cmid = cm.id
INNER JOIN {modules} m ON cm.module = m.id
INNER JOIN (
SELECT * {resource} re WHERE cm.instance = r.id OR
SELECT * {scorm} sco WHERE cm.instance = sco.id OR
SELECT * {glossary} WHERE ON cm.instance = glo.id OR
SELECT * {quiz} qui WHERE cm.instance = qui.id OR
) as r
WHERE LOWER(l.action) LIKE LOWER(:modaction) COLLATE utf8_bin AND l.userid = :userid
GROUP BY l.cmid
ORDER BY MAX(l.time) DESC
Results return NULL values in "resource" names (resourcename, scormname, glossaryname or quizname) and only one valid "resource" name. I render results depending on if result is not null.
But i would like to avoid "filter" by not null result in resourcename, scormname, glossaryname and quizname using PHP.
Thanks!

Answer 1

Something like this maybe - use a union
SELECT l.cmid,
MAX(l.time) as logtime,
cat.id as catid,
cat.name as catname,
c.id as courseid,
c.fullname as coursename,
mods.module,
mods.revision,
mods.name as modname
FROM mdl_log l
JOIN mdl_user u ON l.userid = u.id
JOIN mdl_course c ON l.course = c.id
JOIN mdl_course_categories cat ON c.category = cat.id
JOIN (
SELECT cm.id AS cmid, m.name AS module, r.name, r.revision
FROM mdl_course_modules cm
JOIN mdl_modules m ON cm.module = m.id AND m.name = 'resource'
JOIN mdl_resource r ON r.id = cm.instance
UNION
SELECT cm.id AS cmid, m.name as modulentype, s.name, NULL AS revision
FROM mdl_course_modules cm
JOIN mdl_modules m ON cm.module = m.id AND m.name = 'scorm'
JOIN mdl_scorm s ON s.id = cm.instance
UNION
SELECT cm.id AS cmid, m.name as modulentype, g.name, NULL AS revision
FROM mdl_course_modules cm
JOIN mdl_modules m ON cm.module = m.id AND m.name = 'glossary'
JOIN mdl_glossary g ON g.id = cm.instance
UNION
SELECT cm.id AS cmid, m.name as modulentype, q.name, NULL AS revision
FROM mdl_course_modules cm
JOIN mdl_modules m ON cm.module = m.id AND m.name = 'quiz'
JOIN mdl_quiz q ON q.id = cm.instance
) mods ON mods.cmid = l.cmid AND mods.module = l.module
WHERE l.module IN ('resource', 'scorm', 'glossary', 'quiz')
GROUP BY l.cmid
ORDER BY 1 DESC