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* Custom type where not all elements are comparable
@ 2004-07-05 15:31 Markus Bertheau <twanger@bluetwanger.de>
0 siblings, 2 replies; 3+ messages in thread
From: Markus Bertheau @ 2004-07-05 15:31 UTC (permalink / raw)
To: pgsql-sql
Hi,
Is it possible to define or implement a type in PostgreSQL not all
values of which are comparable to each other? In particular I'm thinking
of a duration type similar to the XML Schema duration type[1]. For
example P2D (2 days) is less than P4D (4 days), but P1M (1 month) and
P30D (30 days) are not comparable.
Thanks.
[1] http://www.w3.org/TR/xmlschema-2/#duration
--
Markus Bertheau <twanger@bluetwanger.de>
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Custom type where not all elements are comparable
@ 2004-07-05 16:32 Tom Lane <tgl@sss.pgh.pa.us>
parent: Markus Bertheau <twanger@bluetwanger.de>
1 sibling, 0 replies; 3+ messages in thread
From: Tom Lane @ 2004-07-05 16:32 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; +Cc: pgsql-sql
Markus Bertheau <twanger@bluetwanger.de> writes:
> Is it possible to define or implement a type in PostgreSQL not all
> values of which are comparable to each other?
Certainly, as long as you don't expect to be able to btree-index it,
sort it, or DISTINCT it. (In theory we could probably handle DISTINCT
using hash aggregation, as long as equality behaves sanely; but that's
not implemented now.)
Probably it'd be reasonable for the comparison operators to return
NULL for a noncomparable pair of inputs.
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Custom type where not all elements are comparable
@ 2004-07-05 19:39 Peter Eisentraut <peter_e@gmx.net>
parent: Markus Bertheau <twanger@bluetwanger.de>
1 sibling, 0 replies; 3+ messages in thread
From: Peter Eisentraut @ 2004-07-05 19:39 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; pgsql-sql
Markus Bertheau wrote:
> Is it possible to define or implement a type in PostgreSQL not all
> values of which are comparable to each other? In particular I'm
> thinking of a duration type similar to the XML Schema duration
> type[1]. For example P2D (2 days) is less than P4D (4 days), but P1M
> (1 month) and P30D (30 days) are not comparable.
Smells like the interval type.
^ permalink raw reply [nested|flat] 3+ messages in thread
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2004-07-05 15:31 Custom type where not all elements are comparable Markus Bertheau <twanger@bluetwanger.de>
2004-07-05 16:32 ` Tom Lane <tgl@sss.pgh.pa.us>
2004-07-05 19:39 ` Peter Eisentraut <peter_e@gmx.net>
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