A word about Db::query()

source/devapi/index.rst

@@ -4,4 +4,5 @@ Developer API
 .. toctree::
    :maxdepth: 2
 
+   querydb
    dbiterator

source/devapi/querydb.rst

@@ -0,0 +1,16 @@
+Querying database
+-----------------
+
+To query database, you can use hte ``$DB::query()`` method.
+
+.. warning::
+
+   Whether this is possible to query database directly using this method, it should be avoid when possible, and you'd better use :doc:`DBIteraor <dbiterator>` instead.
+
+
+To make a database query that could not be done using ``$DB->request()``, like SQL functions call (``NOW()``, ``ADD_DATE()``, ...), you can use the ``query()`` method:
+
+.. code-block:: php
+
+   <?php
+   $DB->query('SELECT id FROM glpi_users WHERE end_date > NOW()');