diff --git a/mod/forum/classes/privacy/provider.php b/mod/forum/classes/privacy/provider.php
index 06466e67df7..a7c96873cad 100644
--- a/mod/forum/classes/privacy/provider.php
+++ b/mod/forum/classes/privacy/provider.php
@@ -37,6 +37,8 @@ use tool_dataprivacy\context_instance;
 
 defined('MOODLE_INTERNAL') || die();
 
+require_once($CFG->dirroot . '/grade/grading/lib.php');
+
 /**
  * Implementation of the privacy subsystem plugin provider for the forum activity module.
  *
@@ -690,35 +692,44 @@ class provider implements
     protected static function export_all_posts(int $userid, array $mappings) {
         global $DB;
 
-        // Find all of the posts, and post subscriptions for this forum.
-        list($foruminsql, $forumparams) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
-        $ratingsql = \core_rating\privacy\provider::get_sql_join('rat', 'mod_forum', 'post', 'p.id', $userid);
-        $sql = "SELECT
-                    p.discussion AS id,
-                    f.id AS forumid,
-                    d.name,
-                    d.groupid
-                  FROM {forum} f
-                  JOIN {forum_discussions} d ON d.forum = f.id
-                  JOIN {forum_posts} p ON p.discussion = d.id
-             LEFT JOIN {forum_read} fr ON fr.postid = p.id AND fr.userid = :readuserid
-            {$ratingsql->join}
-                 WHERE f.id ${foruminsql} AND
-                (
-                    p.userid = :postuserid OR
-                    p.privatereplyto = :privatereplyrecipient OR
-                    fr.id IS NOT NULL OR
-                    {$ratingsql->userwhere}
-                )
-              GROUP BY f.id, p.discussion, d.name, d.groupid
-        ";
+        $commonsql = "SELECT p.discussion AS id, f.id AS forumid, d.name, d.groupid
+                        FROM {forum} f
+                        JOIN {forum_discussions} d ON d.forum = f.id
+                        JOIN {forum_posts} p ON p.discussion = d.id";
+
+        // All discussions with posts authored by the user or containing private replies to the user.
+        list($foruminsql1, $forumparams1) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
+        $sql1 = "{$commonsql}
+                       WHERE f.id {$foruminsql1}
+                         AND (p.userid = :postuserid OR p.privatereplyto = :privatereplyrecipient)";
+
+        // All discussions with the posts marked as read by the user.
+        list($foruminsql2, $forumparams2) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
+        $sql2 = "{$commonsql}
+                        JOIN {forum_read} fr ON fr.postid = p.id
+                       WHERE f.id {$foruminsql2}
+                         AND fr.userid = :readuserid";
+
+        // All discussions with ratings provided by the user.
+        list($foruminsql3, $forumparams3) = $DB->get_in_or_equal(array_keys($mappings), SQL_PARAMS_NAMED);
+        $ratingsql = \core_rating\privacy\provider::get_sql_join('rat', 'mod_forum', 'post', 'p.id', $userid, true);
+        $sql3 = "{$commonsql}
+                 {$ratingsql->join}
+                       WHERE f.id {$foruminsql3}
+                         AND {$ratingsql->userwhere}";
+
+        $sql = "SELECT *
+                  FROM ({$sql1} UNION {$sql2} UNION {$sql3}) united
+              GROUP BY id, forumid, name, groupid";
 
         $params = [
-            'postuserid'    => $userid,
-            'readuserid'    => $userid,
+            'postuserid' => $userid,
+            'readuserid' => $userid,
             'privatereplyrecipient' => $userid,
         ];
-        $params += $forumparams;
+        $params += $forumparams1;
+        $params += $forumparams2;
+        $params += $forumparams3;
         $params += $ratingsql->params;
 
         $discussions = $DB->get_records_sql($sql, $params);
diff --git a/mod/forum/db/install.xml b/mod/forum/db/install.xml
index ef7545dce73..bbda97aba99 100644
--- a/mod/forum/db/install.xml
+++ b/mod/forum/db/install.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<XMLDB PATH="mod/forum/db" VERSION="20191001" COMMENT="XMLDB file for Moodle mod/forum"
+<XMLDB PATH="mod/forum/db" VERSION="20200508" COMMENT="XMLDB file for Moodle mod/forum"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="../../../lib/xmldb/xmldb.xsd"
 >
@@ -99,6 +99,7 @@
         <INDEX NAME="userid" UNIQUE="false" FIELDS="userid"/>
         <INDEX NAME="created" UNIQUE="false" FIELDS="created"/>
         <INDEX NAME="mailed" UNIQUE="false" FIELDS="mailed"/>
+        <INDEX NAME="privatereplyto" UNIQUE="false" FIELDS="privatereplyto" COMMENT="The field is used in certain queries (such as privacy requests) to search for private replies to the user."/>
       </INDEXES>
     </TABLE>
     <TABLE NAME="forum_queue" COMMENT="For keeping track of posts that will be mailed in digest form">
diff --git a/mod/forum/db/upgrade.php b/mod/forum/db/upgrade.php
index 7d36e0413b4..5f709bd6bfa 100644
--- a/mod/forum/db/upgrade.php
+++ b/mod/forum/db/upgrade.php
@@ -246,5 +246,17 @@ function xmldb_forum_upgrade($oldversion) {
     // Automatically generated Moodle v3.9.0 release upgrade line.
     // Put any upgrade step following this.
 
+    if ($oldversion < 2020072100) {
+        // Add index privatereplyto (not unique) to the forum_posts table.
+        $table = new xmldb_table('forum_posts');
+        $index = new xmldb_index('privatereplyto', XMLDB_INDEX_NOTUNIQUE, ['privatereplyto']);
+
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+
+        upgrade_mod_savepoint(true, 2020072100, 'forum');
+    }
+
     return true;
 }
diff --git a/mod/forum/version.php b/mod/forum/version.php
index 7eddcd86571..11f48d60362 100644
--- a/mod/forum/version.php
+++ b/mod/forum/version.php
@@ -24,6 +24,6 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2020061500;       // The current module version (Date: YYYYMMDDXX)
+$plugin->version   = 2020072100;       // The current module version (Date: YYYYMMDDXX)
 $plugin->requires  = 2020060900;       // Requires this Moodle version
 $plugin->component = 'mod_forum';      // Full name of the plugin (used for diagnostics)