Random value from table field

I've varchar(100) field in my users table. I save data there like logo1.png, logo2.png, logo3.png and I'm trying to get data from that field and show random value of it. e.g. logo1.png and second page refresh it's logo3.png etc.

But my problem here is that $random shows sometimes empty e.g. > img src=".png". It shows logos right, but some rand it shows empty.

Can someone help me to make that field to array and that generates random value of user field?

My code:

// In DB: varchar(100) - value: logo1, logo2, logo3

$selected = $row["logo_ids"]; 
$logo = explode(",",trim($row['logo_ids']));

$random = trim($logo[array_rand($logo)]);

echo "example.com/img/". $random .".png";