You can use the DateDiff function to determine how many specified
time intervals exist between two dates. For example, you might use
DateDiff to calculate the number of days between two dates, or the
number of weeks between today and the end of the year.
To calculate the number of days between date1 and date2,
you can use either Day of year ("y") or Day ("d"). When interval is
Weekday ("w"), DateDiff returns the number of weeks between the two
dates. If date1 falls on a Monday, DateDiff counts the number
of Mondays until date2. It counts date2 but not date1.
If interval is Week ("ww"), however, the DateDiff function
returns the number of calendar weeks between the two dates. It counts the
number of Sundays between date1 and date2. DateDiff
counts date2 if it falls on a Sunday; but it doesn't count date1,
even if it does fall on a Sunday.
If date1 refers to a later point in time than date2, the
DateDiff function returns a negative number.
The firstdayofweek argument affects calculations that use the "w"
and "ww" interval symbols.
If date1 or date2 is a date literal, the specified year
becomes a permanent part of that date. However, if date1 or date2
is enclosed in quotation marks (" "), and you omit the year, the current
year is inserted in your code each time the date1 or date2
expression is evaluated. This makes it possible to write code that can be
used in different years.
When comparing December 31 to January 1 of the immediately succeeding
year, DateDiff for Year ("yyyy") returns 1 even though only a day has