• A bit of a strange question.

    I'd never come across the user of parantheses with DISTINCT so assumed it must be some sort of extended syntax I didn't know about. So guessed wrongly that it must have different behaviour.

    But it turned out that the reason I'd never come across it was that there is no alternative syntax at all!

    So an interesting problem to think about, but I can't say I learned anything from it (other than that there are apparently people out there who unnecessarily put brackets with a distinct!)