字符串截取 数据库里某个字段并重新保存到那个字段 C#

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
using SchoolCrm.DBUtility;

namespace SchoolCrm.Web
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {


        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            //string str =@"E:\文档\查询系统\源码\SchoolCrm\Admin\AnLi_Schoolhttp://www.cnblogs.com/../AnLiFile\20121224634919572560504783_安一娜华大I-20.pdf";

            int count = 1;
            DataSet ds = DbHelperSQL.Query(" SELECT  f.* FROM AnLi_ApplySchoolFiles f  ");
            foreach (DataRow item in ds.Tables[0].Rows)
            {
                string str = item["FilesName"].ToString();
                string str2 = str.Substring(str.LastIndexOf("\\") + 1);
                SqlParameter[] parameters = {
                    new SqlParameter("@FilesName1", SqlDbType.NVarChar),
                    new SqlParameter("@FilesId", SqlDbType.NVarChar)};
                parameters[0].Value = str2;
                parameters[1].Value = item["FilesId"].ToString();
                string sqlstr = " update AnLi_ApplySchoolFiles  set FilesName=@FilesName1  where FilesId=@FilesId ";
                int rows = DbHelperSQL.ExecuteSql(sqlstr, parameters);
                if (rows > 0)
                {
                    count++;
                }
            }
            Response.Write(" 成功" + count);

        }


    }
}