Row pattern recognition

On Monday, October 21, 2024, Tatsuo Ishii <ishii(at)postgresql(dot)org> wrote:
>
> I wonder how "PREV(col + 1)" is different from "PREV(col) + 1".
> Currently my RPR implementation does not allow PREV(col + 1). If
> "PREV(col + 1)" is different from "PREV(col) + 1", it maybe worthwhile
> to implement "PREV(col + 1)".
>

Interesting feature that I’m now just seeing.

The expression PREV(column_name) produces a value output taken from the
given named column in the preceding frame row. It doesn’t make any sense
to me to attempt to add the integer 1 to an identifier that is being used
as a value input to a “function”. It would also seem quite odd if “+ 1”
had something to do with row selection as opposed to simply being an
operator “+(column_name%type, integer)” expression.

Maybe RPR is defining something special here I haven't yet picked up on, in
which case just ignore this. But if I read: “UP as price > prev(price +
1)” in the opening example it would be quite non-intuitive to reason out
the meaning. “Price > prev(price) + 1” would mean my current row is at
least one (e.g. dollar per share) more than the value of the previous
period.

David J.