Render sql helps to display the data in grid/table format. You can write sql select statement to display data in the grid format. Please note that since sql statement can be of any type so the default grid function will not work with this sql render. From version 2.4, the pagination, records per page and display of total records is also removed. A better option to use the sql render with the jquery datatable plugin. You can see example here
$pdocrud = new PDOCrud();
$pdocrud->setQuery("select * from orders");
echo $pdocrud->render("SQL");