初学asp.net，前辈帮忙解释下代码

.aspx页面：
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:hyenaTestdbConnectionString %>"
SelectCommand="SELECT [userName], [password], [sex], [age] FROM [userInfo]"></asp:SqlDataSource>

.asp.cs控制语句
string sql = "select * from userInfo";
SqlDataSource1.DataSourceMode = SqlDataSourceMode.DataSet;
SqlDataSource1.SelectCommand = sql;
DataView dv = (DataView)SqlDataSource1.Select(DataSourceSelectArguments.Empty);
foreach (DataRow dr in dv.Table.Rows)
{
Response.Write(dr["userName"]);
Response.Write(dr["password"]);
Response.Write(dr["sex"]);
Response.Write(dr["age"]);
Response.Write("<br>");

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:hyenaTestdbConnectionString %>"
SelectCommand="SELECT [userName], [password], [sex], [age] FROM [userInfo]"></asp:SqlDataSource>

声明一个SqlDataSource,他有一个重要属性ID,这个ID(这里是SqlDataSource1)可以设置为其他数据控件的DataSourceID属性.比如GridView1.DataSourceID = "SqlDataSource1",则该数据控件就可以使用SqlDataSource1里面的数据了.

string sql = "select * from userInfo";// 定义查询语句,从userinfo里查询所有记录.
SqlDataSource1.DataSourceMode = SqlDataSourceMode.DataSet;// SqlDataSource1数据源为数据集模式.
SqlDataSource1.SelectCommand = sql;// 查询命令指定为sql语句.
DataView dv = (DataView)SqlDataSource1.Select(DataSourceSelectArguments.Empty);//用SqlDataSource1的Select方法,通过DataSourceSelectArguments查询参数执行数据筛选.不过你这里参数为空.
foreach (DataRow dr in dv.Table.Rows)
{//逐行输出数据视图(DataView)对象里所有数据