This document contains C# code that connects to a SQL database, retrieves student and class data from tables, and displays it in a Windows Forms application. It opens a SQL connection, uses SQL data adapters to fill DataTables with data from "HocSinh" and "Lop" tables, sets the DataTables as data sources for a data grid view and combo box. It also includes an event handler that populates text boxes with selected row data from the grid.