From ee80a41dd54b86685287f6c2b774c6009e4526c8 Mon Sep 17 00:00:00 2001
From: Tim Hunt <T.J.Hunt@open.ac.uk>
Date: Thu, 11 Apr 2024 13:55:19 +0100
Subject: [PATCH] MDL-74610 quiz: fix grade items query for MySQL

---
 .../local/reports/attempts_report_table.php   | 27 +++++++------------
 question/engine/datalib.php                   |  8 +++++-
 2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/mod/quiz/classes/local/reports/attempts_report_table.php b/mod/quiz/classes/local/reports/attempts_report_table.php
index ef318fb314d..cff27296312 100644
--- a/mod/quiz/classes/local/reports/attempts_report_table.php
+++ b/mod/quiz/classes/local/reports/attempts_report_table.php
@@ -671,28 +671,21 @@ abstract class attempts_report_table extends \table_sql {
      * @param int $gradeitemid the grade item to add information for.
      */
     protected function add_grade_item_mark(int $gradeitemid): void {
+        $dm = new question_engine_data_mapper();
+
         $alias = 'gimarks' . $gradeitemid;
 
-        // This condition roughly filters the list of attempts to be considered.
-        // It is only used in a sub-select to help database query optimisers (see MDL-30122).
-        // Therefore, it is better to use a very simple  which may include
-        // too many records, than to do a super-accurate join.
-        $qubaids = new qubaid_join("{quiz_slots} {$alias}slot2", 'quiza.uniqueid',
-                "{$alias}slot2.quizgradeitemid = :{$alias}gradeitemid2", [$alias . 'gradeitemid2' => $gradeitemid]);
-
-        $dm = new question_engine_data_mapper();
-        [$qalatestview, $viewparams] = $dm->question_attempt_latest_state_view($alias, $qubaids);
-
         $this->sql->fields .= ",\n(
-                SELECT SUM({$alias}.fraction * {$alias}.maxmark) AS summarks
+                SELECT SUM({$alias}qas.fraction * {$alias}qa.maxmark) AS summarks
 
-              FROM {quiz_slots} slot
-              JOIN $qalatestview ON {$alias}.slot = slot.slot
-
-              WHERE slot.quizgradeitemid = :{$alias}gradeitemid
-            ) marks$gradeitemid";
+                  FROM {quiz_slots} {$alias}slot
+                  JOIN {question_attempts} {$alias}qa ON {$alias}qa.slot = {$alias}slot.slot
+                  JOIN {question_attempt_steps} {$alias}qas ON {$alias}qas.questionattemptid = {$alias}qa.id
+                            AND {$alias}qas.sequencenumber = {$dm->latest_step_for_qa_subquery("{$alias}qa.id")}
+                 WHERE {$alias}qa.questionusageid = quiza.uniqueid
+                   AND {$alias}slot.quizgradeitemid = :{$alias}gradeitemid
+            ) AS marks$gradeitemid";
         $this->sql->params[$alias . 'gradeitemid'] = $gradeitemid;
-        $this->sql->params = array_merge($this->sql->params, $viewparams);
     }
 
     /**
diff --git a/question/engine/datalib.php b/question/engine/datalib.php
index 6481e4f9f86..723112fd88d 100644
--- a/question/engine/datalib.php
+++ b/question/engine/datalib.php
@@ -1252,7 +1252,13 @@ ORDER BY
             ) {$alias}", $qubaids->from_where_params());
     }
 
-    protected function latest_step_for_qa_subquery($questionattemptid = 'qa.id') {
+    /**
+     * Get the subquery which selects the latest step for each question_attempt.
+     *
+     * @param string $questionattemptid column alias for the column to join on which is question_attempt.id.
+     * @return string SQL fragment to include in the query. Has not placeholders.
+     */
+    public function latest_step_for_qa_subquery($questionattemptid = 'qa.id') {
         return "(
                 SELECT MAX(sequencenumber)
                 FROM {question_attempt_steps}