This works just fine, thank you!

Using a view is indeed my solution for now. Thanks to all repliers!

The select query I talked about is actually part of an INSERT INTO.... SELECT query.

Does this make a difference?

Yes but here you include the complete select command in the condition.

Problem is here that my real query is very complex (about 40 lines), and putting it 2 times in...

In my opinion, "midnight" doesn't exist in programmers' language.

It equals the beginning of the next day, so my answer is "4"

Correction: I mean "5"

Does this means that Sunday 3 January 2016 is also week 53 in US standards?

removed

I don't believe it's a correct calculation for all situations. It doesn't look at the first day of a week. In Europe that is Monday, in other parts of the...