Hi,

The following statement is untrue: "it is always a good practice to use DATEDIFF method for date comparison instead of making comparison using logical operators (,=)".

As the previous two posters noted, using a function call on an indexed date column (or any indexed column, for that matter) prevents SQL Server from doing an efficient "seek" on the values in that column for that index - all the values need to be retrieved first, then the function applied. If the date column has the highest selectivity, then this can be a severe performance killer.

A safer way to ensure that you get all dates in a certain range, ignoring the "time" component, without applying a function to the source column, is using DateAdd as follows:

--select the correct data type here, DateTime vs SmallDateTime,

-- as you might otherwise incurr another conversion function call

-- on the source column!

DECLARE @FromDate DateTime

DECLARE @ToAndIncludingDate DateTime

SET @FromDate = '2009-04-01'

SET @ToAndIncludingDate = '2009-04-15'

SELECT *

FROM SomeTable

WHERE (SomeColumn >= @FromDate AND SomeColumn < DateAdd(Day, 1, @ToAndIncludingDate) )

HTH,

Tao