Gavin Flower <GavinFlower@archidevsys.co.nz> writes:
> I think that there is a typo in the paragraph: 'x' used instead of 'y'
> in 'GROUP BY'.
You're mistaken. However, possibly the example is a bit confusing,
because the point is that "SELECT *" includes y, which can't be validly
referenced. Maybe we should spell out "x, y" instead of writing "*".
regards, tom lane