Got it, thanks! The string before the method is actually the separator. Right. Thanks.

'I'

Question: if n = 1, does this return 'I' or '\nI'? Thanks!

It works because n is type integer, therefore postgress will perform integer division, that is any decimal will be removed/ignored.

n=5 -> 25/4=6.25 which becomes 6 (3*2)

n=9 -> 81/4=20.25 which becomes 20 (5*4)
etc.

amogus

You should only return one column, column res.

I did it right, I only return numbers. I just wanted to tell that if I insert the # I get the test right, but not the real attempt.

user_id should only contain numbers, not the #. The sample tests only check you return 3 columns and with the proper names. There is no test about the content there.

If I do the test giving '#{number}' as output (with # before), the test passes.
If I do the real attempt, it tells me '{number}' expected but '#{number}' found.

I think it's a bug.

Thank you for the guidelines about the comments and about the exercise. I solve it, thanks again.

Not a kata issue, check your parentheses (where you wrote AS res), and read this: https://docs.codewars.com/training/troubleshooting/#post-discourse

BTW, there is no need to write expression_matter. everywhere, you're doing a select in a single table, you can ommit it.