Reuse of Subselects

[Holger Marzen]

Hi all,

if I have something like this:

SELECT column1,
(... complicated subselect ...),
column1 - (... same subselect as above ...)
FROM table1;

do I really have to rewrite the subselect a 2nd time if I need that
result in another column's expression?

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[Martijn van Oosterhout]

Depend in the exact query, you can do:

SELECT column1, x.c, column1-x.c
FROM table1, (... complicated subselect ...) as x;

The above may not work if they're correlated, so you can try:

SELECT column1, column2, column1-column2
FROM
(SELECT column1, (... complicated subselect ...) as column2
FROM table1);

Hope this helps,

On Tue, Feb 17, 2004 at 01:02:43PM +0100, Holger Marzen wrote:

Hi all,

if I have something like this:

SELECT column1,
(... complicated subselect ...),
column1 - (... same subselect as above ...)
FROM table1;

do I really have to rewrite the subselect a 2nd time if I need that
result in another column's expression?

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--
Martijn van Oosterhout <kl*****@svana.org> http://svana.org/kleptog/ If the Catholic church can survive the printing press, science fiction
will certainly weather the advent of bookwarez.
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[P.J. \Josh\ Rovero]

temporary tables work. Save the complicated
subselect in temporary table, following
queries just simple select on temp table.

Holger Marzen wrote:

Hi all,

if I have something like this:

SELECT column1,
(... complicated subselect ...),
column1 - (... same subselect as above ...)
FROM table1;

do I really have to rewrite the subselect a 2nd time if I need that
result in another column's expression?

--
P. J. "Josh" Rovero Sonalysts, Inc.
Email: ro****@sonalysts.com www.sonalysts.com 215 Parkway North
Work: [phone] or 442-4355 Waterford CT 06385
************************************************** *********************

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[Bruno Wolff III]

On Tue, Feb 17, 2004 at 13:02:43 +0100,
Holger Marzen <ho****@marzen.de> wrote:

Hi all,

if I have something like this:

SELECT column1,
(... complicated subselect ...),
column1 - (... same subselect as above ...)
FROM table1;

do I really have to rewrite the subselect a 2nd time if I need that
result in another column's expression?

You should be able to use a join. The syntax won't be simpler, but you
might get nearly a 2 fold speed up.

Assuming that the subselect depends on the current row, you want to do
something like:

SELECT (
SELECT column1, complicated, column1 - complicated FROM
(complicated select AS complicated) AS comptable)
) FROM table1;

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