Re: Detecting change in event properties

Hello

2013/10/25 Robert James <srobertjames(at)gmail(dot)com>

> On 10/25/13, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Robert James <srobertjames(at)gmail(dot)com> writes:
> >>> (To elaborate, I'm interested in:
> >>> * Finding field x of the _previous_ row
> >>> * Finding field x of the _next_ row
> >>> * Finding field x of the _previous_ row that meets a certain criteria
> >>> (which the current row may or may not meet)
> >>> )
> >
> >> The first two are actually trivial - lag(field_x) over (order by [same
> >> order as query]) and lead(...).
> >
> > Right.
> >
> >> But the last one seems ellusive - How can I find the value of field x
> >> on the previous row WHERE a criteria is met? Is it possible to do this
> >> at all with a window function?
> >
> > I don't see any way to achieve that with any of the built-in window
> > functions, but I believe it could be done by a custom window function.
> > Are you up for some C coding?
>
> Hmmm... certainly nothing I would trust on a production db.
>
> Is there a way to do it without C not using window functions? Perhaps
> with some type of JOIN?
>

you can write a table function with inner loop cycle over cursor

Regards

Pavel

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