Re: plpgsql arrays

From: Tom Lane
Subject: Re: plpgsql arrays
Date: ,
Msg-id: 1138.1238770111@sss.pgh.pa.us
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In response to: Re: plpgsql arrays  (Matthew Wakeling)
Responses: Re: plpgsql arrays  (Matthew Wakeling)
Re: plpgsql arrays  (Nathan Boley)
List: pgsql-performance

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plpgsql arrays  (Matthew Wakeling, )
 Re: plpgsql arrays  (Robert Haas, )
  Re: plpgsql arrays  (Matthew Wakeling, )
   Re: plpgsql arrays  (Tom Lane, )
    Re: plpgsql arrays  (Matthew Wakeling, )
     Re: plpgsql arrays  (Tom Lane, )
      Re: plpgsql arrays  (Matthew Wakeling, )
       Re: plpgsql arrays  (Matthew Wakeling, )
       Re: plpgsql arrays  (Tom Lane, )
        Re: plpgsql arrays  (Matthew Wakeling, )
        Re: plpgsql arrays  (Nathan Boley, )
    Re: plpgsql arrays  (Simon Riggs, )
     Re: plpgsql arrays  (Alvaro Herrera, )
     Re: plpgsql arrays  (Tom Lane, )
      Re: plpgsql arrays  (Matthew Wakeling, )
     Re: plpgsql arrays  (Matthew Wakeling, )
      Re: plpgsql arrays  (Robert Haas, )
 Re: plpgsql arrays  (Tom Lane, )
  Re: plpgsql arrays  (Matthew Wakeling, )
   Re: plpgsql arrays  (justin, )
    Re: plpgsql arrays  (Matthew Wakeling, )
     Re: plpgsql arrays  (justin, )
     Re: plpgsql arrays  (Tom Lane, )
      Re: plpgsql arrays  (Matthew Wakeling, )
   Re: plpgsql arrays  (Merlin Moncure, )
    Re: plpgsql arrays  (Tom Lane, )
     Re: plpgsql arrays  (Matthew Wakeling, )
      Re: plpgsql arrays  (Tom Lane, )
 Re: plpgsql arrays  (Merlin Moncure, )
  Re: plpgsql arrays  (Merlin Moncure, )
   Re: plpgsql arrays  (Matthew Wakeling, )
    Re: plpgsql arrays  (Merlin Moncure, )

Matthew Wakeling <> writes:
> On Fri, 3 Apr 2009, Tom Lane wrote:
>> Not unless you have sorted the inputs in some way that has more
>> knowledge than the "equal" operator represents.  Otherwise you can have
>> elements drop out that might still be needed to match to a later
>> left-hand element.

> Of course. You certainly have to choose a sort order that works. Sorting
> by the start field would be sufficient in this case.

Uh, no, it wouldn't.  Visually:

    L1    -------------------------
    L2    -----------
    L3    ---------------------

    R1                   --------

At L2, you'd conclude that you're done matching R1.

Intuitively, it seems like 1-D "overlaps" is a tractable enough
operator that you should be able to make something merge-like
work.  But it's more complicated than I think you realize.

            regards, tom lane


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