I've deployed QR systems around the world, and created MVPs for retail systems.
Most POS systems are set to scan traditional 1D barcodes. It is likely that whatever solution you come up with, the POS will need to be upgraded.
A QR code can hold up to around 4,000 ASCII characters (it's a bit more complicated than that) - so the code can contain a database ID, URL, contact information - anything you like really.
The complicated bit is what you actually do with the data once scanned. Is it for a loyalty card? Payment? Stock keeping?