Filterering my gridView acording to the selected

public void populateGridView()
       {

           studentMarksTableAdapter = new OleDbDataAdapter();
           studentsDataSet = new DataSet();
           studentMarksTableAdapter.SelectCommand = dbCmd;
           studentMarksTableAdapter.Fill(studentsDataSet, "StudentMarks");
           gridViewAll.DataSource = studentsDataSet.Tables[0];
       }
       private void Form1_Load(object sender, EventArgs e)
       {

           // Connect to Database:
           string sConnection = "Provider = Microsoft.Ace.OLEDB.12.0;Data Source=Students.accdb";
           dbConn = new OleDbConnection(sConnection);
           dbConn.Open();

           //  Connect the Command to the Connection:
           sql = "SELECT  * FROM StudentMarks ";

           dbCmd = new OleDbCommand();
           dbCmd.CommandText = sql;
           dbCmd.Connection = dbConn;


           populateGridView();



           dbConn.Close();
       }

       private void cboFilter_SelectedIndexChanged(object sender, EventArgs e)
       {
           if (cboFilter.Text == "Student Number")
           {
               sql += "Order By StudentNumber ASC";
               populateGridView();
           }
       }