what is count(*) % 2 = 1

Question

I see a query like

select *
from Table1
group by Step
having count(*) % 2 = 1

What is the trick about having count(*) % 2 = 1

Can anyone explain?

edit: What are the common usage areas?

Answer 1

Well % is the modulo operator, which gives the remainder of a division so it would give 0 when the number is exactly divisible by 2 (even) and 1 when not (e.g. it is odd). So the query basically selects elements for which count is odd (as said above).

Answer 2

Would that not be checking if you have an odd number of entries per step?

Answer 3

It will return all the steps which had odd number of rows.