输出参数是字符串还是日期？

Question

Please see the DDL below:

CREATE TABLE TestDate (bookingdate datetime)
INSERT INTO TestDate VALUES ('2013-10-04')

Please see the ADODB recordset below:

rs.open "SELECT bookingdate FROM TestDate"
If rs("bookingdate") > dateadd("yyyy", -6, Now)
  msgbox("test")
end if

The msgbox always appears regardless of what the date in the database is.

I believe I have to do this:

If datevalue(rs("bookingdate")) > dateadd("yyyy", -6, Now)
  msgbox("test")
end if

Then the messagebox only appears if the booking date is within the last six years.

Is bookingdate treated as a string in the first code fragment?

I believe the following webpage would give me the answer: http://www.w3schools.com/ado/ado_datatypes.asp . However, it says Internal Server Error.

Answer 1

You should never write code like this anyway:

If rs("bookingdate") > DateAdd("yyyy", -6, Now)

Instead get in the habit of not relying on the default property, which can backfire on you depending on the usage context. Preferable:

If rs("bookingdate").Value > DateAdd("yyyy", -6, Now)

But a huge piece you left out of the puzzle is what DBMS you are using. Some use some pretty funky data types and call them DATETIME so you probably want to look at both the ADO type of the returned Field and try displaying TypeName(rs("bookingdate").Value) to see what you're ending up with in your code.

If the returned data is of some type such as Decimal or String then all bets are off and you need to go through the right set of gyrations to convert it to something useful before attempting comparisons.