Add an oracle-related note to num_rows() in the documentation
diff --git a/user_guide_src/source/database/results.rst b/user_guide_src/source/database/results.rst
index 4f93c79..de4a337 100644
--- a/user_guide_src/source/database/results.rst
+++ b/user_guide_src/source/database/results.rst
@@ -150,6 +150,13 @@
echo $query->num_rows();
+.. note:: Oracle (OCI8 driver) doesn't have a way of returning the
+ total number of rows in a result set without actually fetching
+ all of them. The only way to achieve this is to get all of the
+ results first and do a ``count()`` on the resulting array,
+ therefore you can't use ``num_rows()`` to increase performance
+ when using the OCI8 driver.
+
$query->num_fields()
=====================