The ISNULL() function is a nasty mysql-ism. The standard SQL syntax is "xxx IS NULL...

diff --git a/lib/accesslib.php b/lib/accesslib.php
index 95e37b00cab575d80fa32a1fe3df48c54de93318..10a4ef6f2ce7bcd8b07f1fc9d08bd639e5c00267 100755 (executable)
--- a/lib/accesslib.php
+++ b/lib/accesslib.php
@@ -2315,7 +2315,7 @@ function get_users_by_capability($context, $capability, $fields='u.*, ul.timeacc
     /// if context is a course, then construct sql for ul
     if ($context->aggregatelevel == CONTEXT_COURSE) {
         $courseid = $context->instanceid;
-        $coursesql = "AND (ul.courseid = $courseid OR ISNULL(ul.courseid))";
+        $coursesql = "AND (ul.courseid = $courseid OR ul.courseid IS NULL)";
     } else {
         $coursesql = '';
     }