Help with changing price after deduction

[Chrisj]

This works successfully:

$wallet = $user->wallet;
$upwallet = ($sell_video == 0 && $wallet >= 1 ? 0.5 : 0);
$db->rawQuery("UPDATE ".T_USERS." SET `wallet` = `wallet`- '".$upwallet."' WHERE `id` = '".$video->user_id."'");

I'd like guidance with adding after that code:
When the sell_video amount is 0 and the wallet amount = 0.5, change/update the sell_video to X.

Any assistance is welcomed.