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Jim C. Nasby
*nix forums Guru Wannabe
Joined: 01 Mar 2005
Posts: 241
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 Posted: Fri Mar 04, 2005 9:47 pm Post subject:
Re: Casting from a domain
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On Fri, Mar 04, 2005 at 03:40:17PM -0500, Tom Lane wrote:
| Quote: | "Jim C. Nasby" <decibel@decibel.org> writes:
decibel=# create cast (interval as rrs.seconds) WITH FUNCTION rrs.interval_to_seconds(interval) AS IMPLICIT;
CREATE CAST
decibel=# select cast('1 month'::interval AS seconds);
ERROR: cannot cast type interval to seconds
Given the current coercion rules, we should probably disallow attempts
to define casts that involve domains. Casts are on base types. The
down-cast from a domain to its base type is hardwired, and the up-cast
from base type to domain is too (with invocation of any constraints
that may apply). Adding random user-defined casts to this would
probably just create confusion and ambiguity. In particular, this
was already meaningless:
decibel=# create domain rrs.seconds as double precision;
CREATE DOMAIN
decibel=# create cast (double precision as rrs.seconds) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST
since the presence of the cast might be thought to justify coercing
floats to "seconds" without invoking domain constraints.
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Yeah, I figured it was probably an issue with it being a domain. I was
looking for a way to do this without the extra work involved in defining
a full-blown type. I guess the good news is I should be able to re-use
all the double-precision functions and what-not for 'seconds'.
BTW, is there a reason 'double' isn't an alias for 'double precision'?
I'm pretty sure every other database I've used (other than oracle of
course) supports 'double'. " precision" is just too much extra typing
after all... 
--
Jim C. Nasby, Database Consultant decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828
Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"
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Tom Lane
*nix forums Guru
Joined: 24 Mar 2005
Posts: 2070
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| Posted: Fri Mar 04, 2005 7:40 pm Post subject:
Re: Casting from a domain
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"Jim C. Nasby" <decibel@decibel.org> writes:
| Quote: | decibel=# create cast (interval as rrs.seconds) WITH FUNCTION rrs.interval_to_seconds(interval) AS IMPLICIT;
CREATE CAST
decibel=# select cast('1 month'::interval AS seconds);
ERROR: cannot cast type interval to seconds
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Given the current coercion rules, we should probably disallow attempts
to define casts that involve domains. Casts are on base types. The
down-cast from a domain to its base type is hardwired, and the up-cast
from base type to domain is too (with invocation of any constraints
that may apply). Adding random user-defined casts to this would
probably just create confusion and ambiguity. In particular, this
was already meaningless:
decibel=# create domain rrs.seconds as double precision;
CREATE DOMAIN
decibel=# create cast (double precision as rrs.seconds) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST
since the presence of the cast might be thought to justify coercing
floats to "seconds" without invoking domain constraints.
regards, tom lane
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Richard Huxton
*nix forums Guru
Joined: 01 Mar 2005
Posts: 522
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| Posted: Fri Mar 04, 2005 6:47 pm Post subject:
Re: Casting from a domain
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Jim C. Nasby wrote:
| Quote: | decibel=# create cast (interval as rrs.seconds) WITH FUNCTION rrs.interval_to_seconds(interval) AS IMPLICIT;
^^^
decibel=# select cast('1 month'::interval AS seconds);
ERROR: cannot cast type interval to seconds
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It's not a schema issue is it? I.E. the lack of "rrs."?
--
Richard Huxton
Archonet Ltd
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Jim C. Nasby
*nix forums Guru Wannabe
Joined: 01 Mar 2005
Posts: 241
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| Posted: Fri Mar 04, 2005 5:49 pm Post subject:
Casting from a domain
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I'm trying to create a seconds domain that is an interval 'mashed to
seconds' as I once saw Tom describe it.
decibel=# create domain rrs.seconds as double precision;
CREATE DOMAIN
decibel=# create cast (double precision as rrs.seconds) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST
decibel=# create function rrs.interval_to_seconds(interval) returns seconds as 'SELECT extract( EPOCH FROM $1 );' LANGUAGE SQL;
CREATE FUNCTION
decibel=# create cast (interval as rrs.seconds) WITH FUNCTION rrs.interval_to_seconds(interval) AS IMPLICIT;
CREATE CAST
decibel=# select cast('1 month'::interval AS seconds);
ERROR: cannot cast type interval to seconds
\dC shows that the cast is there, and rrs.interval_to_seconds works as
expected, and according to \df does return seconds.
Version is 7.4.5.
--
Jim C. Nasby, Database Consultant decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828
Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"
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