How to query wp_postmeta table for any specific meta_value?

Question

I am using following code in the theme files to get some output from the DB:

<?php $querystr = "SELECT DISTINCT meta_value FROM $wpdb->wp_postmeta WHERE 'meta_key' LIKE 'movie_name' ORDER BY meta_value ASC";
$movie_names =  $wpdb->get_results($querystr, OBJECT);
echo sizeof($movie_names);
?>
<ul>
<?php foreach ( $movie_names as $movie_name ){ ?>
   <li><?php echo $movie_name->meta_value; ?> </li>
<?php } ?>
</ul>

Above code's result is "0" at the frontend. But when I am running the same query i.e.

SELECT DISTINCT meta_value FROM wp_postmeta WHERE 'meta_key' LIKE 'movie_name' ORDER BY meta_value ASC

in DB then it's returning 6 rows. Please help me in finding the problem in the code.

Answer 1

$wpdb->wp_postmeta is wrong. Always use just $wpdb->postmeta – without further prefixes.

So...

global $wpdb;

$querystr = "
    SELECT DISTINCT meta_value 
    FROM $wpdb->postmeta 
    WHERE meta_key LIKE 'movie_name' 
    ORDER BY meta_value ASC
";

$movie_names = $wpdb->get_results( $querystr, OBJECT );

if ( ! $movie_names ) {
    $wpdb->print_error(); // Get the last error message for debugging
}
else {
    // Do something awesome with the movies
}