| From: | Greg Stark <stark(at)mit(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, "<pgsql-hackers(at)postgresql(dot)org>" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: join removal |
| Date: | 2009-08-09 16:46:32 |
| Message-ID: | 407d949e0908090946g673d41dcx25405b2da58ac97c@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Aug 9, 2009 at 5:19 PM, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> I am having a hard time wrapping my brain around what it means to have
>> multiple, incompatible notions of equality... any help appreciated!
>
> Well, for instance a complex-number datatype could have one btree
> opclass that sorts on absolute value (distance from 0,0) and another
> opclass that sorts on real part. In the first case "equal" values would
> be members of the same circle around the origin, in the second case they
> are members of the same vertical line.
The example that came to mind for me was a case-insensitive btree
class for text.
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