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* Order of "WITH RECURSIVE" output
@ 2009-07-07 01:44 Andreas Joseph Krogh <andreak@officenet.no>
2009-07-07 01:55 ` Re: Order of "WITH RECURSIVE" output Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 3+ messages in thread
From: Andreas Joseph Krogh @ 2009-07-07 01:44 UTC (permalink / raw)
To: pgsql-sql
Hi all.
Take this example from src/test/regress/sql/with.sql:
WITH RECURSIVE subdepartment(level, id, parent_department, name) AS
(
-- non recursive term
SELECT 1, * FROM department WHERE name = 'A'
UNION ALL
-- recursive term
SELECT sd.level + 1, d.* FROM department AS d, subdepartment AS sd
WHERE d.parent_department = sd.id
)
SELECT * FROM subdepartment ORDER BY name;
level | id | parent_department | name
-------+----+-------------------+------
1 | 1 | 0 | A
2 | 2 | 1 | B
3 | 3 | 2 | C
3 | 4 | 2 | D
4 | 6 | 4 | F
(5 rows)
If I omit "ORDER BY", is the output *guaranteed* (according to some standard) to be ordered in "hierarchy"-order, meaning each parent-department is always output before its respective child, or do I have to calculate a "level" column (like in the example above) and specify "ORDER BY LEVEL" to be 100%?
I'm using WITH RECURSIVE as sub-queries to build up arrays of parents in each output-row and would like as little overhead as possible and hence avoid unnecessary sorting.
--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / CTO
------------------------+---------------------------------------------+
OfficeNet AS | The most difficult thing in the world is to |
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| |
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------------------------+---------------------------------------------+
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Order of "WITH RECURSIVE" output
2009-07-07 01:44 Order of "WITH RECURSIVE" output Andreas Joseph Krogh <andreak@officenet.no>
@ 2009-07-07 01:55 ` Tom Lane <tgl@sss.pgh.pa.us>
2009-07-07 02:06 ` Re: Order of "WITH RECURSIVE" output Andreas Joseph Krogh <andreak@officenet.no>
0 siblings, 1 reply; 3+ messages in thread
From: Tom Lane @ 2009-07-07 01:55 UTC (permalink / raw)
To: Andreas Joseph Krogh <andreak@officenet.no>; +Cc: pgsql-sql
Andreas Joseph Krogh <andreak@officenet.no> writes:
> If I omit "ORDER BY", is the output *guaranteed* (according to some
> standard) to be ordered
No. It's not necessary to read any other details to answer that ...
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Order of "WITH RECURSIVE" output
2009-07-07 01:44 Order of "WITH RECURSIVE" output Andreas Joseph Krogh <andreak@officenet.no>
2009-07-07 01:55 ` Re: Order of "WITH RECURSIVE" output Tom Lane <tgl@sss.pgh.pa.us>
@ 2009-07-07 02:06 ` Andreas Joseph Krogh <andreak@officenet.no>
0 siblings, 0 replies; 3+ messages in thread
From: Andreas Joseph Krogh @ 2009-07-07 02:06 UTC (permalink / raw)
To: pgsql-sql
On Tuesday 07 July 2009 03:55:35 am Tom Lane wrote:
> Andreas Joseph Krogh <andreak@officenet.no> writes:
> > If I omit "ORDER BY", is the output *guaranteed* (according to some
> > standard) to be ordered
>
> No. It's not necessary to read any other details to answer that ...
>
> regards, tom lane
Ok, thanks for prompt reply.
--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / CTO
------------------------+---------------------------------------------+
OfficeNet AS | The most difficult thing in the world is to |
Rosenholmveien 25 | know how to do a thing and to watch |
1414 Trollåsen | somebody else doing it wrong, without |
NORWAY | comment. |
| |
Tlf: +47 24 15 38 90 | |
Fax: +47 24 15 38 91 | |
Mobile: +47 909 56 963 | |
------------------------+---------------------------------------------+
^ permalink raw reply [nested|flat] 3+ messages in thread
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2009-07-07 01:44 Order of "WITH RECURSIVE" output Andreas Joseph Krogh <andreak@officenet.no>
2009-07-07 01:55 ` Tom Lane <tgl@sss.pgh.pa.us>
2009-07-07 02:06 ` Andreas Joseph Krogh <andreak@officenet.no>
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