SQL Server: Floor a date in SQL server, but stay deterministic

Question

(This is related to Floor a date in SQL server.)

Does a deterministic expression exist to floor a DATETIME? When I use this as a computed column formula:

DATEADD(dd, DATEDIFF(dd, 0, [datetime_column]), 0)

the I get an error when I place an index on that column:

Cannot create index because the key column 'EffectiveDate' is non-deterministic or imprecise.

But both DATEDIFF and DATEADD are deterministic functions by definition. Where is the catch? Is it possible?

Answer 1

My guess is that this is a bug of some sorts. In SQL 2005 I was able to create such an indexed view without a problem (code is below). When I tried to run it on SQL 2000 though I got the same error as you are getting.

The following seems to work on SQL 2000, but I get a warning that the index will be ignored AND you would have to convert every time that you selected from the view.

CONVERT(CHAR(8), datetime_column, 112)

Works in SQL 2005:

CREATE TABLE dbo.Test_Determinism (
    datetime_column DATETIME    NOT NULL    DEFAULT GETDATE())
GO

CREATE VIEW dbo.Test_Determinism_View
WITH SCHEMABINDING
AS
    SELECT
        DATEADD(dd, DATEDIFF(dd, 0, [datetime_column]), 0) AS EffectiveDate
    FROM
        dbo.Test_Determinism
GO

CREATE UNIQUE CLUSTERED INDEX IDX_Test_Determinism_View ON dbo.Test_Determinism_View (EffectiveDate)
GO