1. You had lunch already.

2. You already had lunch.
3. You have already had lunch.
4. You have had lunch already.
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Are they all grammatical and the same in meaning? Which one is commonly used?

2 answers

All are correct and, yes, they all mean about the same thing. I'm not sure any of them is more commonly used than the others.
on / still / you / can / help / Saturday / me / ?