From 5db91ce2a43f81adef94e385800523a8df814bf2 Mon Sep 17 00:00:00 2001
From: Dan Poltawski <dan@moodle.com>
Date: Wed, 21 Aug 2013 14:33:44 +0800
Subject: [PATCH] MDL-41191 mod_forum: avoid DISTINCT on TEXT columns

It is not supported by all db engines
---
 mod/forum/lib.php | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index e65dcd21339..d07bacbaadf 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -8149,16 +8149,18 @@ function forum_get_courses_user_posted_in($user, $discussionsonly = false, $incl
     // table and join to the userid there. If we are looking for posts then we need
     // to join to the forum_posts table.
     if (!$discussionsonly) {
-        $joinsql = 'JOIN {forum_discussions} fd ON fd.course = c.id
-                    JOIN {forum_posts} fp ON fp.discussion = fd.id';
-        $wheresql = 'fp.userid = :userid';
-        $params = array('userid' => $user->id);
+        $subquery = "(SELECT DISTINCT fd.course
+                         FROM {forum_discussions} fd
+                         JOIN {forum_posts} fp ON fp.discussion = fd.id
+                        WHERE fp.userid = :userid )";
     } else {
-        $joinsql = 'JOIN {forum_discussions} fd ON fd.course = c.id';
-        $wheresql = 'fd.userid = :userid';
-        $params = array('userid' => $user->id);
+        $subquery= "(SELECT DISTINCT fd.course
+                         FROM {forum_discussions} fd
+                        WHERE fd.userid = :userid )";
     }
 
+    $params = array('userid' => $user->id);
+
     // Join to the context table so that we can preload contexts if required.
     if ($includecontexts) {
         list($ctxselect, $ctxjoin) = context_instance_preload_sql('c.id', CONTEXT_COURSE, 'ctx');
@@ -8169,11 +8171,10 @@ function forum_get_courses_user_posted_in($user, $discussionsonly = false, $incl
 
     // Now we need to get all of the courses to search.
     // All courses where the user has posted within a forum will be returned.
-    $sql = "SELECT DISTINCT c.* $ctxselect
+    $sql = "SELECT c.* $ctxselect
             FROM {course} c
-            $joinsql
             $ctxjoin
-            WHERE $wheresql";
+            WHERE c.id IN ($subquery)";
     $courses = $DB->get_records_sql($sql, $params, $limitfrom, $limitnum);
     if ($includecontexts) {
         array_map('context_instance_preload', $courses);