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MDL-37250 mod_lesson: Move conditions to queries for better performance

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While this ony seems to affect MySQL, better put the filter/conditions
on every query so the temporary view/table does not need to handle
thousands of potentially unrelated records.
This commit is contained in:
Eloy Lafuente (stronk7)
2016-07-12 13:32:46 +02:00
parent 4de30cdce3
commit 3b9f7d90d0
1 changed files with 6 additions and 2 deletions
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mod/lesson/report.php
+6 -2
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@@ -128,19 +128,23 @@ if ($action === 'delete') {
list($esql, $params) = get_enrolled_sql($context, '', $currentgroup, true);
list($sort, $sortparams) = users_order_by_sql('u');
$params['lessonid'] = $lesson->id;
$params['a1lessonid'] = $lesson->id;
$params['b1lessonid'] = $lesson->id;
$params['c1lessonid'] = $lesson->id;
$ufields = user_picture::fields('u');
$sql = "SELECT DISTINCT $ufields
FROM {user} u
JOIN (
SELECT userid, lessonid FROM {lesson_attempts} a1
WHERE a1.lessonid = :a1lessonid
UNION
SELECT userid, lessonid FROM {lesson_branch} b1
WHERE b1.lessonid = :b1lessonid
UNION
SELECT userid, lessonid FROM {lesson_timer} c1
WHERE c1.lessonid = :c1lessonid
) a ON u.id = a.userid
JOIN ($esql) ue ON ue.id = a.userid
WHERE a.lessonid = :lessonid
ORDER BY $sort";
$students = $DB->get_recordset_sql($sql, $params);