Why posts array is empty?

Question

I try to get posts that either do not have a custom field set or if set have a value not like a given parameter.

Here is my code:

    $args_included = array(
        'numberposts'     => 1,
        'post_type'       => 'post',
        'post_status'     => 'published',
        'meta_query' => array(
               'relation' => 'OR',
                array(
                    'key' => 'requested_by',
                    'value' => '%' . $SANITIZED_PARAM . '%',
                    'compare' => 'NOT LIKE'
                ),
                array(
                    'key' => 'requested_by',
                    'compare' => 'NOT EXISTS'
                )
        )
    );

    get_posts($args_included); // empty array

The custom field requested_by is supposed to be either empty or filled with a string value like this one : foo;bar;gamma;.

If I remove this part of the code :

                'relation' => 'OR',
                array(
                    'key' => 'requested_by',
                    'value' => '%' . $SANITIZED_PARAM . '%',
                    'compare' => 'NOT LIKE'
                ),

the query then works.

What am I missing ?

WP 3.5

UPDATE Here is my final code that work :

    $args_included = array(
        'numberposts'     => 1,
        'post_type'       => 'post',
        'post_status'     => 'publish',
        'meta_query' => array(
                array(
                    'key' => 'requested_by',
                    'value' => $PARAM,
                    'compare' => 'NOT LIKE'
                )
        )
    );

    get_posts($args_included); // Just ONE post

Mistakes:

• Status is publish not published

• The custom field didn't exist so no results can be found.
  Below is a SQL query for mass setting the custom field:

  INSERT INTO wp_postmeta(post_id,meta_key,meta_value)
     SELECT ID , 'requested_by', ';'
     FROM wp_posts
     WHERE post_status='publish'
     AND post_type='post'
  

• Last tips for debug purpose. You can get the final SQL query sent to MySQL like this:

  $args = array(
      'numberposts'     => 1,
      'post_type'       => 'post',
      'post_status'     => 'publish',
      'meta_query' => array(
              array(
                  'key' => 'requested_by',
                  'value' => $PARAM,
                  'compare' => 'NOT LIKE'
              )
      )
  );
  
  $q = new WP_Query($args);
  echo $q->request;
  

Answer 1

You don't need to add the % signs to the value. WordPress does that for you automatically on a LIKE or NOT LIKE comparison. You also don't need to "sanitize" the parameter, it will be automatically escaped for SQL.

See wp-includes/meta.php, around line 806 or so.