T-SQL Between Dates Confusion

Question

I am working with T-SQL in SQL Server 2000 and I have a table TRANSACTIONS which has a date column TRANDATE defined as DateTime, among many other c

Answer 1

You have kind of answered your own question already. What you have observed is the way SQL Server works.

If it is confirmation you need, this MSDN document has following to say about it

When the time part is unspecified, it defaults to 12:00 A.M. Note that a row that contains a time part that is after 12:00 A.M. on 1998-0105 would not be returned by this query because it falls outside the range.

Edit

As for your comment, a datetime essentially is a floating point value.

Following script shows what numbers SQL Server works with.
40541.9749 (12/31/2010 23:23:59) can't be included when your upper bound is 40541 (12/31/2010)

DECLARE @ADateTime1 DATETIME
DECLARE @ADateTime2 DATETIME
DECLARE @ADateTime1AsFloat FLOAT
DECLARE @ADateTime2AsFloat FLOAT

SET @ADateTime1 = '12/31/2010'
SET @ADateTime2 = '12/31/2010 23:23:59'

SET @ADateTime1AsFloat = CAST(@ADateTime1 AS FLOAT)
SET @ADateTime2AsFloat = CAST(@ADateTime2 AS FLOAT)

SELECT @ADateTime1AsFloat, @ADateTime2AsFloat