Data modeling with the goal to get the best performance in Oracle and SQL Server
I think you should consider your requirements a bit further and see which model fits better long term. 

Regarding performance: How fast is fast enough? You need a target or goal to work to. And to do that you need to forecast load and volumes.

Ignoring performance and thinking about data models: personally i like the 2nd option because it can give you an audit trail. You can see which items were sold on which days, and can handle things like returns or stock take adjustments. This makes reporting, accounting and auditing easier.