以下是小弟的程式碼
這次都能順利正常的運作了
但搜尋按鈕按下去後 沒有再一次的回傳我要的sql資料
我以為是sql的擺放位置有錯，但調整了幾次後發現沒解決
上網搜尋後好像都沒人犯這個新手錯誤

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace 試作.搜尋引擎
{
    public partial class 搜尋2 : System.Web.UI.Page
    {
        string Search_String = "";
        SqlConnection sqlconn = new SqlConnection();
        protected void Page_Load(object sender, EventArgs e)
        {
           /* string mainconn = ConfigurationManager.ConnectionStrings["G HConnectionString"].ConnectionString;
            SqlConnection sqlconn = new SqlConnection(mainconn);
            sqlconn.Open();
            SqlCommand sqlcomm = new SqlCommand();
            sqlcomm.Connection = sqlconn;
            DataSet AAA = new DataSet();
            SqlDataAdapter sda = new SqlDataAdapter(sqlcomm);
            SqlDataSource1.SelectParameters.Clear();*/

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            string mainconn = ConfigurationManager.ConnectionStrings["G HConnectionString"].ConnectionString;
            SqlConnection sqlconn = new SqlConnection(mainconn);
            sqlconn.Open();
            SqlCommand sqlcomm = new SqlCommand();
            sqlcomm.Connection = sqlconn;
            DataSet AAA = new DataSet();
            SqlDataAdapter sda = new SqlDataAdapter(sqlcomm);
            SqlDataSource1.SelectParameters.Clear();

            string Search_String = "";
            Boolean u_select = false;
            int word_length = 0;

            for (int i = 0; i < DDL1.Items.Count; i++)
            {
                if (DDL1.Items[i].Selected)
                {
                    Search_String += DDL1.Items[i].Text;
                    u_select = true; /*這邊要判斷是真*/

                }

            }


            if (u_select)
            {
                string Left(string param, int length)
                {

                    string result = param.Substring(0, length);

                    return result;
                }
                        word_length = Search_String.Length; /*length 要用英文的長度來判斷*/

                        Search_String = Left(Search_String, (word_length)); /*length 要看情況使用-or+*/

                        TextBox1.Text = Search_String;

                
            }


            else
                {

                    Label1.Text = "您尚未點選任何一個DowndropList子選項";

                    return;
                }

           

            SqlDataSource1.SelectCommand = "SELECT * FROM  [dbo].[ptt123] where [內文] like '%Search_String%'";


        }




       /* String sqlquery = "select * from [dbo].[ptt123] where 內文 like '%'+@Search_String+'%'";*/

        protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = ConfigurationManager.ConnectionStrings["G HConnectionString"].ToString();
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "select * from [dbo].[ptt123]";
            cmd.Connection = con;
            SqlDataReader rd = cmd.ExecuteReader();
            object dt = null;
            GridView1.DataSource = dt;
            GridView1.DataBind();

        }

        protected void GridView2_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = ConfigurationManager.ConnectionStrings["G HConnectionString"].ToString();
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "SELECT [日期], [內文], [留言] FROM  [dbo].[ptt123] where [內文] like '%Search_String%'";
            cmd.Connection = con;
            SqlDataReader rd = cmd.ExecuteReader();
            object dt = null;
            GridView2.DataSource = dt;
            GridView2.DataBind();
        }

        protected void SqlDataSource1_Selecting(object sender, SqlDataSourceSelectingEventArgs e)
        {

        }


    }


}