//绑定数据的方法

 private void GetDB(string str)

        {

            //SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=StuManage;Integrated Security=True");

            //con.Open();

            //SqlDataAdapter sdr = new SqlDataAdapter();

            //SqlCommand cmd = new SqlCommand(str, con);

            //sdr.SelectCommand = cmd;

            //DataSet ds = new DataSet();

            con = new SqlConnection("Data Source=.;Initial Catalog=StuManage;Integrated Security=True");

            con.Open();

            sdr = new SqlDataAdapter();

            sdb = new SqlCommandBuilder(sdr);

            cmd = new SqlCommand(str,con);

            sdr.SelectCommand = cmd;

            ds = new DataSet();

            sdr.Fill(ds);

            //向gridview中添加列

            DataGridViewTextBoxColumn col_txb_Id = new DataGridViewTextBoxColumn();

            col_txb_Id.HeaderText = "课程编号";

            col_txb_Id.DataPropertyName = "cno";

            dataGridView1.Columns.Add(col_txb_Id);



            DataGridViewTextBoxColumn col_txb_Name = new DataGridViewTextBoxColumn();

            col_txb_Name.HeaderText = "课程名";

            col_txb_Name.DataPropertyName = "cname";

            dataGridView1.Columns.Add(col_txb_Name);



            DataGridViewTextBoxColumn col_txb_Score = new DataGridViewTextBoxColumn();

            col_txb_Score.HeaderText = "课程学分";

            col_txb_Score.DataPropertyName = "ccredit";

            dataGridView1.Columns.Add(col_txb_Score);



            Da