How to retrieve the search related data from the database to a listitem?

Question 1

This can be done using textbox and autocomplete, please see full example from the following reference:

http://www.aspdotnetcodes.com/AutoComplete_From_Database.aspx

Question 2

you can try this -

    <!doctype html>

<html lang="en">

<head>

  <meta charset="utf-8">

  <title>jQuery UI Autocomplete - Default functionality</title>

  <link rel="stylesheet" href="//code.jquery.com/ui/1.10.4/themes/smoothness/jquery-ui.css">

  <script src="//code.jquery.com/jquery-1.10.2.js"></script>

  <script src="//code.jquery.com/ui/1.10.4/jquery-ui.js"></script>

  <link rel="stylesheet" href="/resources/demos/style.css">

  <script>

  $(function() {

    var availableTags = [

      "ActionScript",

      "AppleScript",

      "Asp",

      "BASIC",

      "C",

      "C++",

      "Clojure",

      "COBOL",

      "ColdFusion",

      "Erlang",

      "Fortran",

      "Groovy",

      "Haskell",

      "Java",

      "JavaScript",

      "Lisp",

      "Perl",

      "PHP",

      "Python",

      "Ruby",

      "Scala",

      "Scheme"

    ];

    $( "#tags" ).autocomplete({

      source: availableTags

    });

  });

  </script>

</head>

<body>



<div class="ui-widget">

  <label for="tags">Tags: </label>

  <input id="tags">

</div>

</body>

</html>

To get the data from database we will need to build a handler that will process all the requests of AutoComplete and return the results back to the ASP.Net Web page.

    <%@ WebHandler Language="C#" Class="Search_CS" %>

using System;
using System.Web;
using System.Data.SqlClient;
using System.Configuration;
using System.Text;

public class Search_CS : IHttpHandler {

    public void ProcessRequest (HttpContext context) {
        string prefixText = context.Request.QueryString["q"];
        using (SqlConnection conn = new SqlConnection())
        {
            conn.ConnectionString = ConfigurationManager
                    .ConnectionStrings["constr"].ConnectionString;
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandText = "select ContactName from Customers where " +
                "ContactName like @SearchText + '%'";
                cmd.Parameters.AddWithValue("@SearchText", prefixText);
                cmd.Connection = conn;
                StringBuilder sb = new StringBuilder(); 
                conn.Open();
                using (SqlDataReader sdr = cmd.ExecuteReader())
                {
                    while (sdr.Read())
                    {
                        sb.Append(sdr["ContactName"])
                            .Append(Environment.NewLine);
                    }
                }
                conn.Close();
                context.Response.Write(sb.ToString()); 
            }
        }
    }

    public bool IsReusable {
        get {
            return false;
        }
    }
}