DateTime Column Not Using Index

I'm having a hard time getting one of my tables to use a non clustered index that I have on a DateTime column.

A sample version of the table is something like this


CREATE TABLE Appointments
(
ID INT NOT NULL,
AppointmentDate DateTime NOT NULL
)

with a clustered primary key on ID and a nonclustered key on AppointmentDate.

This production table has over 1million rows and the problem I have is this:



If I do a SELECT * FROM Appointments where AppointmentDate >= '20060701' AND AppointmentDate < '20060702' the Non clustered index on the AppointmentDate column works fine. i.e. I'm returning all appointments for the 1st of July.



Now if I run the exact same query using datetime parameters, a Clustered index scan is performed instead of an index seek.

DECLARE @AppDate DateTime

SET @AppDate = '20060701'

SELECT * FROM Appointments WHERE AppointmentDate >= @AppDate and AppointmentDate < DATEADD(day, 1, @AppDate)





Any ideas why it would do this?