How to sort by custom field value?

Question

I am using these code to sort most Commented, Most viewed Posts

<?php $params = $_GET;
unset($params['orderby']);
unset($params['order']);
unset($params['v_orderby']);
unset($params['v_sortby']);
$url = $_SERVER["HTTP_HOST"].$_SERVER["REQUEST_URI"];
$url = strtok($url, '?');
$url =$url.'?'.http_build_query($params);
?>
 <ul id="sort">
<li <?php if($active == "date"): ?> class="active"<? endif ?>><a href="http://<?php echo   
$url ?>">Most Rated</a></li>
<li <?php if($active == "comment"): ?> class="active"<? endif ?>><a  href="http://<?php   echo $url ?>&orderby=comment_count&order=desc">Most commented </a></li>
<li <?php if($active == "views"): ?> class="active"<? endif ?>><a href="http://<?php echo $url ?>&v_sortby=views&v_orderby=desc">Most viewed </a></li>
</ul>

Now I want to sort Custom Field "Rating" as Most Rated here is the code of custom field.

 <?php
//grab the rating value
$rating = get_post_meta($post->ID, 'rating', true);

//prints star image
for ($i=1; $i<=$rating; $i++){
    echo '<img src="/images/star.png"/>';  
}

//prints unstar image
for ($i=$rating; $i<10; $i++){
    echo '<img src="/images/unstar.png"/>';
}
?>

For this I used this code, but it's not working.

<a href="http://<?php echo $url ?>&orderby=rating&order=desc">Most Rated</a>  

Answer 1

From what I understood from your question, you want to sort your result by the most rated custom field 'rating' which is assumed to be number. In order to do this you need to write the below wp_query argument and to handle it properly in your request. However the end result for your query should be as follows:

$args = array(
      'meta_key' => 'rating',
      'order'   =>  'DESC',
      'orderby' => 'meta_value_num'
);
$query = new WP_Query($args);