Documentation: Warn against using object fields in MySQL and MariaDB

docs/en/reference/types.rst

@@ -479,6 +479,14 @@ using deserialization or ``null`` if no data is present.
     properly on vendors not supporting column comments and will fall back to
     ``text`` type instead.
 
+.. warning::
+
+    While the built-in ``text`` type of MySQL and MariaDB can store binary data,
+    ``mysqldump`` cannot properly export ``text`` fields containing binary data.
+    This will cause creating and restoring of backups fail silently. A workaround is
+    to ``serialize()``/``unserialize()`` and ``base64_encode()``/``base64_decode()``
+    PHP objects and store them into a ``text`` field manually.
+
 .. warning::
 
     Because the built-in ``text`` type of PostgreSQL does not support NULL bytes,