check if any custom field with certain name has value

I’m trying to show content, when either one of four custom fields is used.

I’m trying to show a link to the online shop for a certain record if it’s entered. I have 4 custom fields available for this.

I have this

<p class="buy">Buy online:
	<?php $key = "beatport"; $bietport = get_post_meta($post->ID, $key, true); if ($bietport) { ?><a href="<?php $key="beatport"; echo get_post_meta($post->ID, $key, true); ?>">Beatport</a><?php } ?>
	<?php $key = "junodownload"; $juno = get_post_meta($post->ID, $key, true); if ($juno) { ?><a href="<?php $key="junodownload"; echo get_post_meta($post->ID, $key, true); ?>">Juno</a><?php } ?>
	<?php $key = "rushhour"; $rh = get_post_meta($post->ID, $key, true); if ($rh) { ?><a href="<?php $key="rushhour"; echo get_post_meta($post->ID, $key, true); ?>">Rush Hour</a><?php } ?>
	<?php $key = "discogs"; $dg = get_post_meta($post->ID, $key, true); if ($dg) { ?><a href="<?php $key="discogs"; echo get_post_meta($post->ID, $key, true); ?>">Discogs</a><?php } ?>
</p>

I’ve tried this code but doesn’t work. It always gives Yes, even if no values are entered. It works with 1 value, but when more values come into play, it doesn’t anymore…

<?php
	$bietport = get_post_meta($post->ID, $beatport, true);
	$juno = get_post_meta($post->ID, $junodownload, true);
	$rh = get_post_meta($post->ID, $rushhour, true);
	$dg = get_post_meta($post->ID, $discogs, true);
	if ($bietport || $juno || $rh || $dg) { ?>
		YES
<?php } else { ?>
		NO
<?php } ?>

The first part should come where it says YES and no will be removed (if I get it working)
Hoping somebody knows an answer…