diff --git a/lib/dao/dao.class.php b/lib/dao/dao.class.php
index de9ec2c0ec..c81772b6ae 100755
--- a/lib/dao/dao.class.php
+++ b/lib/dao/dao.class.php
@@ -428,6 +428,20 @@ class dao
         echo $this->processSQL();
     }
 
+    /**
+     * Explain sql. 
+     * 
+     * @param  string $sql 
+     * @access public
+     * @return void
+     */
+    public function explain($sql = '')
+    {
+        $sql    = empty($sql) ? $this->processSQL() : $sql;
+        $result = $this->dbh->query('explain ' . $sql)->fetch();
+        a($result);
+    }
+
     /**
      * Process the sql, replace the table, fields.
      *