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;        };