Performing MySQLi searches that contain URL encoded strings

Question

I am having trouble retrieving data from a database, when the field contains a URL encoded string.

What I mean is, my MySQLi database contains a field called "artist_name", where some of the values contain URL encoded strings, such as:

• "Sonny+O'Brien"
• "Lil'+Joe"
• "Batman+&+Robin"

etc.

When I search on these fields in PhpMyAdmin, it finds them straight away, using a select statement:

SELECT * FROM `artists` WHERE `artist_name` LIKE 'Sonny+O'Brien';

However, when I try the same thing programmatically, from within my PHP script, it returns no results:

$artist_name = "Sonny+O'Brien";
$sql = "SELECT * FROM artists WHERE artist_name LIKE '".$artist_name."'";
if ( $result = $mysqli->query( $sql ) ) {
    $obj = $result->fetch_object();
}

No results.

I have tried using an addslashes() on the artist's name, and I have double-checked all the value's and I am providing them exactly as they appear in the database.

Any ideas why the URL escaped strings are not recognised in my SELECT queries?

edit: (screenshot from PhpMyAdmin, showing that my data is stored as described, and that my SELECT query works from within PhpMyAdmin, just not from my PHP script).