c#简单数据库操作代码

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Server.MapPath("app_data/sdr.mdb");
        string sql;
        switch (DropDownList2.SelectedValue) {
            case "插入数据":
             
                sql = "insert into userinfo(sname,spwd) values('MM','sym')";
                OleDbCommand cmd = new OleDbCommand(sql, conn);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
                break;
            case "删除数据":
                sql = "delete * from userinfo";
                OleDbCommand cmd1 = new OleDbCommand(sql, conn);
                conn.Open();
                cmd1.ExecuteNonQuery();
                conn.Close();
                break;
            case "读取数据":
                sql = "select * from userinfo";
                OleDbCommand cmd2 = new OleDbCommand(sql, conn);
                conn.Open();

                OleDbDataReader dr = cmd2.ExecuteReader();
                if (dr.Read())
                {
                    Response.Write(dr[1]);
                }
                else
                {
                    Response.Write ("Roung");
                }

                conn.Close();
                break;
            case"更新数据":
                sql = "update userinfo set sname='张海波',spwd='sym'";
                OleDbCommand cmd3 = new OleDbCommand(sql, conn);
                conn.Open();
                cmd3.ExecuteNonQuery();
                conn.Close();
                break;
        };