Datepart(year, …) vs. Year(…)

Question

What are the advantages of using one over the other in the following:

DATEPART(YEAR, GETDATE())

As opposed to:

YEAR(GETDATE         


        

Answer 1

Actually - using YEAR(..) is preferably for me, since it's considered a deterministic function, so if I use this in a computed column definition

ALTER TABLE dbo.MyTable
ADD YearOfDate AS YEAR(SomeDateColumn)

I can make this column persisted (and store it into the table):

ALTER TABLE dbo.MyTable
ADD YearOfDate AS YEAR(SomeDateColumn) PERSISTED

This does not work for DATEPART(YEAR, SomeDateColumn) (don't ask me why - just noticed this heuristically).

The same applies to MONTH(SomeDate) vs. DATEPART(MONTH, SomeDate).

If you have tables that you need to select from based on the month and year of a date (like SalesDate or something), then having month and years as persisted computed columns (and indexing them) can be a huge performance boost.