GridView循环显示问题？

Question

一个GridView，一个DropDownList，一个Button ，
DropDownList为（0，最近7天），（1，最近15天），（2，最近30天），（3，查询所有）
当button点击时，根据DropDownList的SelectedIndex值查询。
该怎么循环查询好些呢。    protected void btn_cha_Click(object sender, EventArgs e)
    {
        if (ddl7.SelectedIndex == 0)
        {
            GridView1.DataSource = null;
            string sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<7 and user_name='" + Session["userName"] + "'";
            SqlConnection con = new SqlConnection(conString);
            con.Open();
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr = cmd.ExecuteReader();
            GridView1.DataSource = sdr;
            GridView1.DataBind();
            con.Close();
            sdr.Close();
        }
        if (ddl7.SelectedIndex == 1)
        {
            GridView1.DataSource = null;
            string sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<15 and user_name='" + Session["userName"] + "'";
            SqlConnection con = new SqlConnection(conString);
            con.Open();
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr = cmd.ExecuteReader();            GridView1.DataSource = sdr;
            GridView1.DataBind();
            con.Close();
            sdr.Close();
        }
        if (ddl7.SelectedIndex == 2)
        {
            GridView1.DataSource = null;
            string sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<30 and user_name='" + Session["userName"] + "'";
            SqlConnection con = new SqlConnection(conString);
            con.Open();
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr = cmd.ExecuteReader();
            GridView1.DataSource = sdr;
            GridView1.DataBind();
            con.Close();
            sdr.Close();
        }
        if (ddl7.SelectedIndex == 3)
        {
            GridView1.DataSource = null;
            string sql = "select * from [jinhuo] where user_name='" + Session["userName"] + "'";
            SqlConnection con = new SqlConnection(conString);
            con.Open();
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr = cmd.ExecuteReader();
            GridView1.DataSource = sdr;
            GridView1.DataBind();
            con.Close();
            sdr.Close();
        }
    }

Answer 1

唯一不同的就是条件，所以你把查询封装到一个方法中，传入条件，就不用这么罗嗦的写一堆一样的东西了
还可以对datatable进行本地筛选，这样就不用频繁访问数据库了

Answer 2

别的不说，如下private void ExecSql(string sql)
{
            GridView1.DataSource = null;
            SqlConnection con = new SqlConnection(conString);
            con.Open();
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr = cmd.ExecuteReader();
            GridView1.DataSource = sdr;
            GridView1.DataBind();
            con.Close();
            sdr.Close();
}    protected void btn_cha_Click(object sender, EventArgs e)
    {
            string sql = "";
        if (ddl7.SelectedIndex == 0)
        {
            sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<7 and user_name='" + Session["userName"] + "'";
        }
        if (ddl7.SelectedIndex == 1)
        {
           sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<15 and user_name='" + Session["userName"] + "'";
        }
        if (ddl7.SelectedIndex == 2)
        {
            sql = "select * from [jinhuo] where datediff(day,j_date,'" + DateTime.Now.ToShortDateString() + "')<30 and user_name='" + Session["userName"] + "'";
        }
        if (ddl7.SelectedIndex == 3)
        {
            sql = "select * from [jinhuo] where user_name='" + Session["userName"] + "'";
        }
        ExecSql(sql);
    }