> Note that I am doing mere string comparison. I am comparing the string
'20170817' against the string '20170816'.
>
> Will the XPath always work?
>


It will always work if the dates are valid dates in the Gregorian calendar
between years 0 and 9999, always represented by 4 digits, and if your default
collation isn't something pathological where digits collate out of order.

(Come to think of it, it's not totally pathological for a collation to ignore
leading zeroes in an all-numeric string, so perhaps you're only safe with
dates from 1000AD to 9999AD)

Michael Kay
Saxonica