What is AJAX ?

AJAX stands for Asynchronous JavaScript and XML. AJAX is a new technique for creating better, faster, and more interactive web applications with the help of XML, HTML, CSS and Java Script.

Conventional web application transmit information to and from the sever using synchronous requests. This means you fill out a form, hit submit, and get directed to a new page with new information from the server.

With AJAX when submit is pressed, JavaScript will make a request to the server, interpret the results and update the current screen. In the purest sense, the user would never know that anything was even transmitted to the server.

Client Side HTML file

Now lets have our client side HTML file which is ajax.html and it will have following code

Example -

<html>
   <body>
      
      <script language = "javascript" type = "text/javascript">
         
      </script>
		
      <form name = 'myForm'>
         Max Age: <input type = 'text' id = 'age' /> <br />
         Max WPM: <input type = 'text' id = 'wpm' />
         <br />
         
         Sex: <select id = 'sex'>
            <option value = "m">m</option>
            <option value = "f">f</option>
         </select>
			
         <input type = 'button' onclick = 'ajaxFunction()' value = 'Query MySQL'/>
			
      </form>
      
      <div id = 'ajaxDiv'>Your result will display here</div>
   </body>
</html>

Server Side PHP file

So now your client side script is ready. Now we have to write our server side script which will fetch age, wpm and sex from the database and will send it back to the client. Put the following code into "ajax-example.php" file.

Example -

<?php
   
   $dbhost = "localhost";
   $dbuser = "dbusername";
   $dbpass = "dbpassword";
   $dbname = "dbname";
   
   //Connect to MySQL Server
   mysql_connect($dbhost, $dbuser, $dbpass);
   
   //Select Database
   mysql_select_db($dbname) or die(mysql_error());
   
   // Retrieve data from Query String
   $age = $_GET['age'];
   $sex = $_GET['sex'];
   $wpm = $_GET['wpm'];
   
   // Escape User Input to help prevent SQL Injection
   $age = mysql_real_escape_string($age);
   $sex = mysql_real_escape_string($sex);
   $wpm = mysql_real_escape_string($wpm);
   
   //build query
   $query = "SELECT * FROM ajax_example WHERE sex = '$sex'";
   
   if(is_numeric($age))
   $query .= " AND age <= $age";
   
   if(is_numeric($wpm))
   $query .= " AND wpm <= $wpm";
   
   //Execute query
   $qry_result = mysql_query($query) or die(mysql_error());
   
   //Build Result String
   $display_string = "<table>";
   $display_string .= "<tr>";
   $display_string .= "<th>Name</th>";
   $display_string .= "<th>Age</th>";
   $display_string .= "<th>Sex</th>";
   $display_string .= "<th>WPM</th>";
   $display_string .= "</tr>";
   
   // Insert a new row in the table for each person returned
   while($row = mysql_fetch_array($qry_result)) {
      $display_string .= "<tr>";
      $display_string .= "<td>$row[name]</td>";
      $display_string .= "<td>$row[age]</td>";
      $display_string .= "<td>$row[sex]</td>";
      $display_string .= "<td>$row[wpm]</td>";
      $display_string .= "</tr>";
   }
   echo "Query: " . $query . "<br />";
   
   $display_string .= "</table>";
   echo $display_string;
?>