[#131] Optimise user attempts sql query

catalyst · Mar 30, 2023 · 4420bbc · 4420bbc
1 parent 1b8098a
commit 4420bbc
Showing 1 changed file with 8 additions and 6 deletions.
diff --git a/classes/quiz.php b/classes/quiz.php
@@ -605,12 +605,14 @@ private function get_quiz_attempts(int $quizid): \stdClass {
         $finishedusers = array();
 
         $sql = 'SELECT userid, state
-                   FROM {quiz_attempts}
-                  WHERE id IN (
-                        SELECT MAX(id)
-                          FROM {quiz_attempts}
-                         WHERE quiz = ?
-                      GROUP BY userid)';
+                  FROM {quiz_attempts} qa
+                  JOIN (
+                      SELECT MAX(id) id
+                      FROM {quiz_attempts}
+                      WHERE quiz = ?
+                      GROUP BY userid)
+                    AS qb
+                    ON qa.id = qb.id';
 
         $params = array($quizid);