Get query results for all date values besides current month

I need to get values for data excluding current month and taking this year into account.

What I currently have is the following

WHERE 1=1
    AND CAST(created_at AS DATE) >= '2018-01-01'
    AND MONTH(CAST(created_at AS DATE)) != MONTH(GETDATE())

​x
 
WHERE 1=1    AND CAST(created_at AS DATE) >= '2018-01-01'    AND MONTH(CAST(created_at AS DATE)) != MONTH(GETDATE())​

Obviously this will also exclude 2018 current month data as well which I want to prevent.

I’ve checked different solutions online but failed to apply it.

Answer

I would simply do:

where created_at < dateadd(day, 1 - day(getdate()), cast(getdate as date))

 
where created_at < dateadd(day, 1 - day(getdate()), cast(getdate as date))​

This is also sargable — a mouthful that means that an index can be used for the query.

You can also write this as:

where created_at < datefromparts(year(getdate()), month(getdate()), 1)

 
where created_at < datefromparts(year(getdate()), month(getdate()), 1)​

This is actually better and clearer.