How do you test if something is older than 3 months?

Question

I have been having some trouble to select the rows of my table which has a date of 3 months prior of today. I tried using DATE(NOW() - INTERVAL 3 MONTH) in my where

Answer 1

Use dateadd().

update [TCTdb].[dbo].[Stock]
set [WareHouse] = 'old'
where [ManufacturedDate] < dateadd(month,-3,getdate())

I suggest dateadd() over datediff() because I think you're going to get unexpected results using datediff() with the month datepart.

Consider that the following statements both return 3:

select datediff(month, '1/1/2011','4/1/2011')
select datediff(month, '1/1/2011','4/30/2011')

Either works in this particular case... Just keep that behavior in mind.