Обсуждение: virtual (COMPUTED BY) columns?

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Hi.

These fields do not use any disk space, as the data in them is
derived on the fly.

For example:
CREATE TABLE T_EXAMPLE (
SOME_DATE DATE,
JDATE     COMPUTED BY EXTRACT(JULIAN FROM SOME_DATE)
);

A work-around is to create a function, and reference it in every
query, but storing them in the table definition is the "tidy",
low-maintenance way to do it.

Thanks
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am  Sun, dem 28.01.2007, um 10:25:33 -0600 mailte Ron Johnson folgendes:
> Hi.
>
> These fields do not use any disk space, as the data in them is
> derived on the fly.
>
> For example:
> CREATE TABLE T_EXAMPLE (
> SOME_DATE DATE,
> JDATE     COMPUTED BY EXTRACT(JULIAN FROM SOME_DATE)
> );
>
> A work-around is to create a function, and reference it in every
> query, but storing them in the table definition is the "tidy",
> low-maintenance way to do it.

Was this a question how to do this in PostgreSQL?

You can use a VIEW. Just create T_EXAMPLE ( SOME_DATE DATE );
and then

CREATE VIEW view_example AS SELECT some_date, EXTRACT(JULIAN FROM
some_date) AS julian_date FROM T_EXAMPLE;


Andreas
--
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID:   0x3FFF606C, privat 0x7F4584DA   http://wwwkeys.de.pgp.net

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On 01/28/07 10:43, A. Kretschmer wrote:
> am  Sun, dem 28.01.2007, um 10:25:33 -0600 mailte Ron Johnson folgendes:
>> Hi.
>>
>> These fields do not use any disk space, as the data in them is
>> derived on the fly.
>>
>> For example:
>> CREATE TABLE T_EXAMPLE (
>> SOME_DATE DATE,
>> JDATE     COMPUTED BY EXTRACT(JULIAN FROM SOME_DATE)
>> );
>>
>> A work-around is to create a function, and reference it in every
>> query, but storing them in the table definition is the "tidy",
>> low-maintenance way to do it.
>
> Was this a question how to do this in PostgreSQL?
>
> You can use a VIEW. Just create T_EXAMPLE ( SOME_DATE DATE );
> and then
>
> CREATE VIEW view_example AS SELECT some_date, EXTRACT(JULIAN FROM
> some_date) AS julian_date FROM T_EXAMPLE;

Good point.

But then you have 2 bits of metadata, and yet one more object to
update when you add a column.

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