如果我以 dd-MM-yy 格式传递日期，则将日期以 yyyy-MM-dd 格式保存到 SQL Server 2008

我正在尝试将日期保存到SQL Server 2008数据库中。我已经将日期转换为dd/MM/yyyy格式，即使日期以yyyy-MM-dd格式存储在数据库中。我的按钮点击代码：

protected void Submit_Click(object sender, EventArgs e)
{
    DateTime fdate = DateTime.ParseExact(txtDate.Text, "dd/MM/yyyy", CultureInfo.InvariantCulture);
    sample = fdate;
}
public class sample
{
    public string sample(DateTime fdate)
    {
       string qry = "insert into sample values('"+fdate+"')";
       SqlDataReader dr = conn.query(qry);
    }
}

数据库日期（列）数据类型为 date 。我可以知道原因吗？？
我的其他课程

  public class Connection
{
    SqlConnection conn;
    SqlCommand cmd;
    public SqlDataAdapter ad;
    public DataTable dt = new DataTable();
    public void connclose()
    {
        conn.Close();
    }
    public Connection()
    {
        conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString);
        cmd = null;
    }
  //------------------ connection string---------------------------------------------------------
  ---------------------//
    public string nonquery(string qry)
    {
        string str;
        if (conn.State == ConnectionState.Open)
        {
            conn.Close();
        }
            conn.Open();
        cmd=new SqlCommand(qry, conn);
        str=cmd.ExecuteNonQuery().ToString();
        conn.Close();
        return str;
    }
    public SqlDataReader query(string qry)
    {
        if (conn.State == ConnectionState.Open)
        {
            conn.Close();
        }
        conn.Open();
        cmd = new SqlCommand(qry, conn);
        SqlDataReader dr = cmd.ExecuteReader();
        return dr;
    }

public string sample(DateTime fdate)
{
    string qry = "insert into sample values( @date )";
    using (var cn = new SqlConnection("connection string here") )
    using (var cmd = new SqlCommand(qry, cn))
    {
        cmd.Parameters.Add("@date", SqlDbType.DateTime).Value = fdate;
        cn.Open();
        using (var dr = cmd.ExecuteReader())
        {
            //use dr here...
        }
    }
}