From 8b0d254f0562330846f1a28d79e86866b0ce148f Mon Sep 17 00:00:00 2001
From: John Beedell <john.beedell@open.ac.uk>
Date: Thu, 5 Jan 2017 14:34:41 +0000
Subject: [PATCH] MDL-57511 Quiz: Attempts report shows non-unique debugging

---
 lib/enrollib.php                               | 4 ++++
 mod/quiz/report/attemptsreport_table.php       | 3 ++-
 mod/quiz/report/overview/tests/report_test.php | 8 ++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/enrollib.php b/lib/enrollib.php
index 452a8991ddc..8bb17af486c 100644
--- a/lib/enrollib.php
+++ b/lib/enrollib.php
@@ -1179,6 +1179,10 @@ function is_enrolled(context $context, $user = null, $withcapability = '', $only
  * Returns an array of joins, wheres and params that will limit the group of
  * users to only those enrolled and with given capability (if specified).
  *
+ * Note this join will return duplicate rows for users who have been enrolled
+ * several times (e.g. as manual enrolment, and as self enrolment). You may
+ * need to use a SELECT DISTINCT in your query (see get_enrolled_sql for example).
+ *
  * @param context $context
  * @param string $prefix optional, a prefix to the user id column
  * @param string|array $capability optional, may include a capability name, or array of names.
diff --git a/mod/quiz/report/attemptsreport_table.php b/mod/quiz/report/attemptsreport_table.php
index 87e31bcac95..539df5af3d3 100644
--- a/mod/quiz/report/attemptsreport_table.php
+++ b/mod/quiz/report/attemptsreport_table.php
@@ -389,7 +389,8 @@ abstract class quiz_attempts_report_table extends table_sql {
     public function base_sql(\core\dml\sql_join $allowedstudentsjoins) {
         global $DB;
 
-        $fields = $DB->sql_concat('u.id', "'#'", 'COALESCE(quiza.attempt, 0)') . ' AS uniqueid,';
+        // Please note this uniqueid column is not the same as quiza.uniqueid.
+        $fields = 'DISTINCT ' . $DB->sql_concat('u.id', "'#'", 'COALESCE(quiza.attempt, 0)') . ' AS uniqueid,';
 
         if ($this->qmsubselect) {
             $fields .= "\n(CASE WHEN $this->qmsubselect THEN 1 ELSE 0 END) AS gradedattempt,";
diff --git a/mod/quiz/report/overview/tests/report_test.php b/mod/quiz/report/overview/tests/report_test.php
index 46cdafcfd35..79c19282eab 100644
--- a/mod/quiz/report/overview/tests/report_test.php
+++ b/mod/quiz/report/overview/tests/report_test.php
@@ -90,6 +90,14 @@ class quiz_overview_report_testcase extends advanced_testcase {
             $DB->insert_record('quiz_attempts', $data);
         }
 
+        // This line is not really necessary for the test asserts below,
+        // but what it does is add an extra user row returned by
+        // get_enrolled_with_capabilities_join because of a second enrolment.
+        // The extra row returned used to make $table->query_db complain
+        // about duplicate records. So this is really a test that an extra
+        // student enrolment does not cause duplicate records in this query.
+        $generator->enrol_user($student2->id, $course->id, null, 'self');
+
         // Actually getting the SQL to run is quite hard. Do a minimal set up of
         // some objects.
         $context = context_module::instance($quiz->cmid);