From 83c4b6d01e824c1011bf05dc3a2ee00eb88b7ea9 Mon Sep 17 00:00:00 2001
From: Michael Aherne <michael.aherne@strath.ac.uk>
Date: Tue, 4 Dec 2018 13:01:07 +0000
Subject: [PATCH] MDL-64216 privacy: Split query to use indexes.

---
 grade/classes/privacy/provider.php | 33 ++++++++++++++++++------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/grade/classes/privacy/provider.php b/grade/classes/privacy/provider.php
index b5ea2e4de18..b740003f297 100644
--- a/grade/classes/privacy/provider.php
+++ b/grade/classes/privacy/provider.php
@@ -211,25 +211,32 @@ class provider implements
               JOIN {context} ctx
                 ON ctx.instanceid = gi.courseid
                AND ctx.contextlevel = :courselevel
-         LEFT JOIN {grade_grades} gg
+              JOIN {grade_grades} gg
                 ON gg.itemid = gi.id
-               AND (gg.userid = :userid1 OR gg.usermodified = :userid2)
-         LEFT JOIN {grade_grades_history} ggh
+             WHERE gg.userid = :userid1 OR gg.usermodified = :userid2";
+        $params = [
+            'courselevel' => CONTEXT_COURSE,
+            'userid1' => $userid,
+            'userid2' => $userid
+        ];
+        $contextlist->add_from_sql($sql, $params);
+
+        $sql = "
+            SELECT DISTINCT ctx.id
+              FROM {grade_items} gi
+              JOIN {context} ctx
+                ON ctx.instanceid = gi.courseid
+               AND ctx.contextlevel = :courselevel
+              JOIN {grade_grades_history} ggh
                 ON ggh.itemid = gi.id
-               AND (
-                   ggh.userid = :userid3
-                OR ggh.loggeduser = :userid4
-                OR ggh.usermodified = :userid5
-            )
-             WHERE gg.id IS NOT NULL
-                OR ggh.id IS NOT NULL";
+             WHERE ggh.userid = :userid1
+                OR ggh.loggeduser = :userid2
+                OR ggh.usermodified = :userid3";
         $params = [
             'courselevel' => CONTEXT_COURSE,
             'userid1' => $userid,
             'userid2' => $userid,
-            'userid3' => $userid,
-            'userid4' => $userid,
-            'userid5' => $userid,
+            'userid3' => $userid
         ];
         $contextlist->add_from_sql($sql, $params);