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CREATE TABLE country
(
   id tinyint(4) NOT NULL auto_increment,
   country varchar(20) NOT NULL default '',
   PRIMARY KEY  (id)
) TYPE=MyISAM;CREATE TABLE city
(
  id tinyint(4) NOT NULL auto_increment,
  city varchar(50) default NULL,
  countryid tinyint(4) default NULL,
  PRIMARY KEY  (id)
) TYPE=MyISAM;

Now let’s look at the html code, let’s look at the code of the form and its elements

<form method=”post” action=”" name=”form1″>
Country : <select name=”country” nChange=”getCity(’findcity.php?country=’+this.value)”>
 <option value=”">Select Country</option>
 <option value=”1″>USA</option>
 <option value=”2″>Canada</option>
     </select>
<br />City : <div id=”citydiv”>
 <select name=”select”>
 <option>Select City</option>
     </select>
 </div>
</form>

As you can see that when the dropdown named “country” is changed the “getCity” function is called. Look at the other dropdown carefully, it is inside the division called “citydiv”.

Now let’s look at the javascript function called “getCity”

function getCity(strURL)
{         
 var req = getXMLHTTP(); // fuction to get xmlhttp object
 if (req)
 {
  req.onreadystatechange = function()
 {
  if (req.readyState == 4) { //data is retrieved from server
   if (req.status == 200) { // which reprents ok status                    
     document.getElementById(’citydiv’).innerHTML=req.responseText;
  }
  else
  { 
     alert(”There was a problem while using XMLHTTP:\n”);
  }
  }            
  }        
req.open(”GET”, strURL, true); //open url using get method
req.send(null);
 }
}

now we’ve to create the file called findcity.php and put the following PHP code

<? $country=$_GET['country'];
$link = mysql_connect(’localhost’, ‘root’, ”); /change the configuration if required
if (!$link) {
  die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(’db_ajax’); //change this if required
$query=”select city from city where countryid=$country”;
$result=mysql_query($query);?>
<select name=”city”>
<option>Select City</option>
<? while($row=mysql_fetch_array($result)) { ?>
   <option value><?=$row['city']?></option>
<? } ?>
</select>

Thats all, whenever you change the dropdown of country the values of the city dropdown is automaticalled changed without refreshing the page.

When a search engine visits the dynamic url like product.php?id=5 it does not give much importance to that URL as search engine sees “?” sign treat it as a url which keeps on changing. so we’re converting the dynamic URL like the product.php?id=5 to static url format like product-5.html. We’ll rewrite the url in such a way that in browser’s address bar it will display as a product-5.html but it actually calls the file product.php?id=5. So that why these kind of URL also named as SEO friendly URL.

what is required for URL rewriting ??

To rewrite the URL you must have the mod_rewrite module must be loaded in apache server. And furthermore, FollowSymLinks options also need to be enabled otherwise you may encounter 500 Internal Sever Error.

Examples of url rewriting for seo friendly URL

For rewriting the URL, you should create a .htaccess file in the root folder of your web directory. And have to put the following codes as your requirement.

Options +FollowSymlinks
RewriteEngine on
RewriteRule ^(.*)\.htm$ $1.php [nc]

The following example will rewrite the test.php to test.html i.e when a URL like http://localhost/test.htm is called in address bar it calls the file test.php. As you can see the regular expression in first part of the RewriteRule command and $1 represents the first regular expression of the part of the RewriteRule and [nc] means not case sensitive.

Options +FollowSymlinks
RewriteEngine on
RewriteRule ^product-([0-9]+)\.html$ products.php?id=$1

The following example will rewrite the product.php?id=5 to porduct-5.html i.e when a URL like http://localhost/product-5.html calls product.php?id=5 automatically.

Here is a small technique for you, you can use .html or .asp file to work as a php file i.e. use .asp or .html extension instead of .php. You just need to create a .htaccess file and put the following code in the .htaccess file. Remember that the .htaccess file should be placed in the root folder of your website.

# Make PHP code look like asp or perl code
AddType application/x-httpd-php .asp .pl

if you place the the above code in the .htaccess file then you can use contact.asp as the name of the file. Now a visitor thought that it is a ASP file but this file contains the codes of PHP.

You can put the following code in .htaccess file to work .htm or .html file as PHP file.

# Make all PHP code look like HTML
AddType application/x-httpd-php .htm .html