Wordpress not executing mysql_query()

Question

I have updated an old version of Wordpress (3.0.1) to 4.4.2. Everything works, except for one plugin, which has all queries in this style. I have used a custom page to test a simple query and can verify that the query returns nothing:

$query = "SELECT code FROM wp_kk_video WHERE id = '0'";
$result = mysql_query ($query);

Then I replaced that query with the following:

$query = $wpdb->get_row( "SELECT code FROM wp_kk_video WHERE id = '0'" );
$result = $query->code;

And it worked perfectly.

So why has Wordpress stopped executing the old type of mysql_query queries?

Answer 1

mysql_* has been deprecated and now its not available in newer versions of Php.

Suggestions:

Use PHP 5.3+ or 5.4+ (PHP 5.5+ PHP 5.6+ PHP 7.0+ PHP 7.1+ is not supported for now).

Or use mysqli_* extension for WordPress 4.4.

Or in the last change queries as per wordpress $wpdb->get_row .

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Wpdb Class References:

Answer 2

Plugins should always use the wpdb class/variable abstraction, so that updates like yours don't break your blog as Wordpress code already looks which mysql* functions are available.

Also they offer prepared statements which should be used to prevent SQL injection attacks. If the id parameter in your example is a user provided value and therefore possible evil input, you should rewrite it to the following to be on the secure side:

$wpdb->query( $wpdb->prepare( 
    "SELECT code FROM wp_kk_video WHERE id = '%d'", 
    $video_id
) );