Multiple selection listbox and display records from database

You can use following method :
First select the SelectionMode Property of Listbox to Multiple

Now on button click event you can use this method





 SqlConnection con = new SqlConnection("Put here Your Connection string");
            con.Open();
            string str="select * from tablename where Student_Name in (";
            int ln;
            foreach (ListItem lt in ListBox1.Items)
            {
                if (lt.Selected)
                {
                    str += "'"+lt.ToString()+"'"+",";
                }

               

            }

            ln = str.Length;
            str = str.Substring(0, ln - 1);

            str += ")";

            SqlCommand com = new SqlCommand(str, con);
            SqlDataAdapter da = new SqlDataAdapter(com);

            DataTable tab = new DataTable();
            da.Fill(tab);
            GridView1.DataSource = tab;
            GridView1.DataBind();

            con.Close();