_asp Foundation of DateDiff function parameter description in ASP

DateDiff function

Describe
Returns the time interval between two dates.
Grammar
DateDiff (interval, date1, date2 [, firstdayofweek][, FirstWeekOfYear]])
The syntax for the DATEDIFF function has the following parameters:

Parameter description
Interval must be selected. A string expression that is used to calculate the time interval between Date1 and Date2. For numeric values, see the "Settings" section.
Date1, Date2 must choose. An expression of a date. Two dates used for the calculation.
FirstDayOfWeek Optional. Specifies the constant for the first day of the week. If not specified, the default is Sunday. For numeric values, see the "Settings" section.
FirstWeekOfYear Optional. Specifies a constant for the first week of the year. If not specified, the default is the week of January 1. For numeric values, see the "Settings" section.

Set up
The interval parameter can have the following values:
Set description
YYYY years
Q Quarter
M month
Y number of days in a year
D-Day
W Number of days in a week
WW Week
H hours
M minutes
s seconds

The FirstDayOfWeek parameter can have the following values:

Constant numerical description
Vbusesystem 0 uses the regional language Support (NLS) API settings.
Vbsunday 1 week day (default)
Vbmonday 2 weeks A
Vbtuesday 3 week Two
Vbwednesday 4 week Three
Vbthursday 5 week Four
Vbfriday 6 Friday
Vbsaturday 7 Saturday

The FirstWeekOfYear parameter can have the following values:

Constant numerical description
Vbusesystem 0 uses the regional language Support (NLS) API settings.
VbFirstJan1 1 begins on the week of January 1 (default).
vbFirstFourDays 2 begins with the first week of at least four days in the new year.
Vbfirstfullweek 3 begins with the first full week of the new Year.

Description
The DateDiff function is used to determine the number of specified time intervals that exist between two dates. For example, you can use DateDiff to calculate the number of days between two date differences, or the day to the last day of the year.
To calculate the number of days between Date1 and Date2, you can use "Days of the Year" ("Y") or "Day" ("D"). When interval is the number of days of the Week ("W"), DateDiff returns the number of weeks between two dates. If the date1 is Monday, then DateDiff calculates the number of Monday before Date2. This result contains date2 and does not contain date1. If interval is "Week" ("WW"), the DateDiff function returns the number of weeks between two dates in the Calendar table. function calculates the number of Sunday between Date1 and Date2. If the date2 is Sunday, DateDiff will calculate the date2, but even if Date1 is Sunday, it will not calculate date1.

If Date1 is later than Date2, the DateDiff function returns a negative number.
The FirstDayOfWeek parameter affects computations that use the "w" and "ww" interval symbols.

If  date1  or  date2  is a date literal, the specified year becomes a fixed part of the date. However, if  date1  or  date2  is included in quotation marks   (" ")   and the year is omitted, then the  date1  or   is computed every time in the code When you date2  an expression, the current year is inserted. This allows you to write program code that works for different years. When  interval  is "year" ("yyyy"), compare  12  month  31  day and next year  1  month  1  day, although actually only a day difference ,datediff  return  1  indicates a difference of one year.