Re: join removal

Greg Stark <stark@mit.edu>

From: Greg Stark <stark@mit.edu>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Robert Haas <robertmhaas@gmail.com>, "<pgsql-hackers@postgresql.org>" <pgsql-hackers@postgresql.org>

Date: 2009-08-09T16:46:32Z

Lists: pgsql-hackers

On Sun, Aug 9, 2009 at 5:19 PM, Tom Lane<tgl@sss.pgh.pa.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.

-- 
greg
http://mit.edu/~gsstark/resume.pdf