It depends on what your limiting factor is (any combination):
in reply to perl mysql full table scan
If time is not a limiting factor, then it doesn't matter which method you pick :)
- Network bandwidth
- Processing power
If Memory is not a limiting factor, move your database to a ramdisk.
If Network bandwidth is not a limiting factor (but at least one of the others is), you'd have to benchmark both options.
If Processing power is not a limiting factor, you could just let mysql do it's thing (least effort).
Also something that might matter...how often do you have to perform a query like this? If the answer is more than 'occasionally', consider letting mysql index the column.