at a restaurant, and in a restaurant, what's the difference?

Hello.

Please help me,,,,

I'm on "preposition lesson" today,
and I found that both sentences, A chef works at a restaurant and A chef works in a restaurant, are okay.

Are there any different nuance in each sentence?
What's the difference between at and in????

In practice, there is no difference between the two phrases, but sometimes there is a nuance. In certain situations, "In a restaurant" can mean effectively "inside a restaurant", whereas "at a restaurant" can mean "at the site of a restaurant".

I agree with Mick......nothing I can add to that. Except perhaps to say, on reflection, that I reckon I would most usually say "I had a great meal last night at a restaurant in town".

In this context, "in town" means the city centre as opposed to local suburban.