Problem in update grid's item when using join in render_sql

when I using JOIN statement in my query it just load my items from db correctly but when I want to edit item in grid by double click on it or drag on drop it,it makes red and don’t store changes.
code of server side is like this:

	mysql_set_charset("UTF8", $res);

	$grid = new GridConnector($res);
	ConnectorSecurity::$security_key = true;
	$query="SELECT *
        FROM group_bank_question JOIN question ON";
        "id","id, name, content");

please help me,thanks.

This is expected
In case of complex SQL query for data selecting, you need to define a separate SQL for data saving or use your own code for data saving. … omdatabase … lexqueries