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4GuysFromRolla.com : ASP FAQS : Databases, Queries


Question:

(1) How can I have two dates and select all records that have a date field with a value between those two dates? (2) How can I select all records in a given month?


[Print this FAQ]

Answer: (1) For the purposes of answering the first question, we will assume that both dates are entered into a form on the prior page by the user:

<%
' note: if either date entered by the user is invalid,
'     the call to CDate will fail with an error.
firstDate = CDate( Request.Form("startDate") )
lastDate = CDate( Request.Form("endDate") )

SQL = "SELECT * FROM table WHERE theDateField BETWEEN #" & firstDate & "# AND #" & lastDate & "#"
...
%>


That code works for an Access database. Only Access surrounds literal dates with #...#. For any other database use

<%
SQL = "SELECT * FROM table WHERE theDateField BETWEEN '" & firstDate & "' AND '" & lastDate & "'"
%>


See CAUTION below!

(2) There are probably several ways to find all records in a given month, but this way should work universally for all databases. It relies on a quirk in the DateSerial function, but it is a quirk that is well described in the Microsoft VBScript documentation.

Again, for ease of demonstration, we will assume that the year and month to be used come from form fields on the prior page:

<%
' what year and month did the user choose?
' (again, if the numbers are not valid CInt will give an error)
theYear = CInt( Request.Form("chosenYear") )
theMonth = CInt( Request.Form("chosenMonth") )

' find first day of the given month...
firstDate = DateSerial( theYear, theMonth, 1 ) ' day 1 of theMonth in theYear
' now comes the "quirk" from the MS documentation:
lastDate = DateSerial( theYear, theMonth + 1, 0 )

SQL = "SELECT * FROM table WHERE theDateField BETWEEN #" & firstDate & "# AND #" & lastDate & "#"
...
%>


The quirk in DateSerial is this: If you ask for a month or day out of range, then the out of range value is converted by quite logical means to the best corresponding day. So if you give 13 as the month, DateSerial figures out you want January of the year after the given year. And if you give 0 as the day, then DateSerial figures out you want the day before the first day of the given month, which is of course the last day of the prior month!

Again, the form shown is for an Access DB. Change each # character to a ' for any other DB.



CAUTION! If the field you are checking, in either of these sets of code, actually contains a DateTIME value (that is, if there is a time component to the value of the field), then the code will not work in all cases! Reason: A date alone is considered to be the same as that date at midnight of that day!

So if the field in the DB is (say) April 2, 2002 9:30:10 AM and you are looking for fields with values between March 17, 2002 AND April 2, 2002 ... well, you won't find that record! Because 9:30:10 AM is *after* midnight and so is not between the two given dates.

In Access, this is easy to fix: Just use DateValue(theDateField) in place of the bare date field! This strips off the time part of the field and now the comparisons all make sense! For other DBs, check the documentation to see if they have a functionality equivalent to DateValue. (Incidentally, VBScript as used in ASP also has the DateValue function, so you could check the VBS manual to see how it works, if need be.)

FAQ posted by Bill Wilkinson at 10/16/2000 6:24:23 PM to the Databases, Queries category. This FAQ has been viewed 63,400 times.

Do you have a FAQ you'd like to suggest? Suggestions? Comments? If so, send it in! Also, if you'd like to be a FAQ Admin (creating/editing FAQs), let me know! If you are looking for other FAQs, be sure to check out the 4Guys FAQ and Commonly Asked Messageboard Questions!

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Last computed at 9/17/2007 3:22:00 AM


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