Use INNER JOIN in queries

main/exercise/exercise.php

@@ -1022,22 +1022,24 @@ $hotpotatoes_exist = false;
 
 if ($is_allowedToEdit) {
     $sql = "SELECT d.path as path, d.comment as comment, ip.visibility as visibility
-            FROM $TBL_DOCUMENT d, $TBL_ITEM_PROPERTY ip
+            FROM $TBL_DOCUMENT d 
+            INNER JOIN $TBL_ITEM_PROPERTY ip
+            ON (d.id = ip.ref AND d.c_id = ip.c_id)
             WHERE
                 d.c_id = $courseId AND
                 ip.c_id = $courseId AND                
-                d.id = ip.ref AND
                 ip.tool = '".TOOL_DOCUMENT."' AND
                 (d.path LIKE '%htm%') AND
                 d.path  LIKE '".Database :: escape_string($uploadPath.'/%/%')."'
             LIMIT ".$from.",".$limit; // only .htm or .html files listed
 } else {
     $sql = "SELECT d.path as path, d.comment as comment, ip.visibility as visibility
-            FROM $TBL_DOCUMENT d, $TBL_ITEM_PROPERTY ip
+            FROM $TBL_DOCUMENT d 
+            INNER JOIN $TBL_ITEM_PROPERTY ip
+            ON (d.id = ip.ref AND d.c_id = ip.c_id)
             WHERE
                 d.c_id = $courseId AND
                 ip.c_id = $courseId AND                
-                d.id = ip.ref AND
                 ip.tool = '".TOOL_DOCUMENT."' AND
                 (d.path LIKE '%htm%') AND
                 d.path  LIKE '".Database :: escape_string($uploadPath.'/%/%')."' AND