Which is correct?
Thank you.
That is what I think too. But I heard earlier today a Chinese host say 'Please all rise', which I don't think is correct.
The event was the Shanghai Expo opening ceremony, where the host said it in English asking all to stand up in response to kind of anthem playing thing.
To be honest "Please, all rise" isn't exactly wrong, it just doesn't sound as good as the other way round. If the sentence were longer, then it would be a different story:
Please, all rise for the national anthem of ........ etc.
But as a short, 3-word phrase, I think "All rise, please" simply sounds neater.
To me, yes! It's a little different from saying "Please do this right now" where you wouldn't necessarily pause. When you're inviting someone to do something in a rather polite way, I would pause slightly after please. I'm sure other people here will disagree with me and say there is no pause and therefore no comma needed.
I think "Would you please all rise for..." or "And now let us all rise for..." sounds more familiar, but I agree that with the pause, it doesn't sound abnormal.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.