Facebook's user id's go up to 2^32 .. which by my count it 4294967296.
mySQL's unsigned int's range is 0 to 4294967295 (which is 1 short - or my math is wrong) and its unsigned big int's range is 0 to 18446744073709551615
int = 4 bytes, bigint = 8 bytes
OR
Do I store it as a string?
varchar(10) = ? bytes
How will it effect efficiency, I heard that mysql handle's numbers far better than strings (performance wise). So what do you guys recommend
Because Facebook assigns the IDs, and not you, you must use BIGINTs.
Facebook does not assign the IDs sequentially, and I suspect they have some regime for assigning numbers.
I recently fixed exactly this bug, so it is a real problem.
I would make it UNSIGNED, simply because that is what it is.
I would not use a string. That makes comparisons painful and your indexes clunkier than they need to be.
Your math is a little wrong... remember that the largest number you can store in N bytes is 2^(N) - 1... not 2^(N). There are 2^N possible numbers, however the largest number you can store is 1 less that.
If Facebook uses an unsigned big int, then you should use that. They probably don't assign them sequentially.
Yes, you could get away with a varchar... however it would be slower (but probably not as much as you are thinking).
I would just stick with INT. It's easy, it's small, it works and you can always change the column to a larger size in the future if you need to.
FYI:
VARCHAR(n) ==> variable, up to n + 1 bytes
CHAR(n) ==> fixed, n bytes
