经典ASP，IIS6和IIS8之间的DATE区别

Question

I am helping to migrate a classic asp website (front end) and ms access database (back end) from a Windows 2003 IIS6 server to a Windows 2012 IIS 8.5 server. I am having a problem with this query in particular;

sqlquery1 = "Select RentalNum, CarID, RentalStatus, StartDate, EndDate from table where CDate(EndDate) <= CDate('"&Date()&"') order by CDate(EndDate) desc"

On the existing system all is ok. On the new system the returned results are not <= "todays date". The results show some dates before today and some after. The database date fields are just "text" (I didn't set it up) and whilst my initial thoughts were to change the schema to proper dates, I would like to understand the problem, particularly as there are many of parts of the system using similar queries using date() and CDate. Are there underlying dates differences between IIS servers? I have looked at browser locality and all is ok there.

Any pointers?

Answer 1

Examine this expression used in your query:

CDate('"&Date()&"')

The Date() function returns the system date as a Date/Time value. But then that expression adds quotes before and after the Date/Time value, which transforms it to a string value. And then CDate() takes that string and transforms it back to a Date/Time value again.

Hopefully that description convinces you those manipulations are at best wasted effort. However if the two servers have different date format settings, the dates resulting from that full CDate() expression could be different.

I'm not positive that is the source of your problem, but you can easily eliminate the possibility. The Access db engine supports the Date() function, so you can use it directly without first transforming it to a string and then back into a Date/Time value.

sqlquery1 = "Select RentalNum, CarID, RentalStatus, StartDate, EndDate " & _
    "from [table] where CDate(EndDate) <= Date() order by CDate(EndDate) desc"

If that change does not solve the problem, next examine those EndDate text values and make sure they're interpreted as the date you expect:

SELECT EndDate, CDate(EndDate) AS EndDate_as_date
FROM [table];

You mentioned your "initial thoughts were to change the schema to proper dates" . I think that is the best way to go because developement based on dates as Date/Time is saner than with dates as strings.