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Special column trivia 3+ messages / 3 participants [nested] [flat]
* Special column trivia @ 2010-06-06 07:18 Greg Smith <[email protected]> 2010-06-06 10:30 ` Re: Special column trivia Tom Lane <[email protected]> 0 siblings, 1 reply; 3+ messages in thread From: Greg Smith @ 2010-06-06 07:18 UTC (permalink / raw) To: pgsql-docs I was just reading http://www.postgresql.org/docs/9.0/static/ddl-system-columns.html and noted that the second part about the ctid being unstable: "a row's ctid will change if it is updated or moved by VACUUM FULL" is probably not true anymore. Is that worth updating? What got me reading that section was a rather weird documentation question/addition from Edmund Horner. He noted that the following works on PG8.4 and 9.0: postgres=# select (row(1,2)).name; name ------- (1,2) Having not worked on earlier versions (this from 8.3): postgres=# select (row(1,2)).name; ERROR: could not identify column "name" in record data type I didn't see anything that documents the ability to use "name" to refer to the composite record like this. Since it's not an area of the code I'm familiar with, so I'm just baffled as Edmund. "Row Constructors" at http://www.postgresql.org/docs/current/interactive/sql-expressions.html and "Composite Value Input" at http://www.postgresql.org/docs/current/interactive/rowtypes.html both seem relevant, but don't seem to explain what's happening. That second one is where he pointed out confusion can really creep in, because "name" is also a field in the inventory_item table, which makes it particularly easy for a coding error to refer to the wrong thing oddly. -- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support [email protected] www.2ndQuadrant.us ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Special column trivia 2010-06-06 07:18 Special column trivia Greg Smith <[email protected]> @ 2010-06-06 10:30 ` Tom Lane <[email protected]> 2010-06-10 22:00 ` Re: Special column trivia Bruce Momjian <[email protected]> 0 siblings, 1 reply; 3+ messages in thread From: Tom Lane @ 2010-06-06 10:30 UTC (permalink / raw) To: Greg Smith <[email protected]>; +Cc: pgsql-docs Greg Smith <[email protected]> writes: > I was just reading > http://www.postgresql.org/docs/9.0/static/ddl-system-columns.html and > noted that the second part about the ctid being unstable: "a row's ctid > will change if it is updated or moved by VACUUM FULL" is probably not > true anymore. Is that worth updating? It's still true. VACUUM FULL still reassigns ctids. > What got me reading that section was a rather weird documentation > question/addition from Edmund Horner. He noted that the following works > on PG8.4 and 9.0: > postgres=# select (row(1,2)).name; This is the cast-a-composite-type-to-string-type issue that's come up in several guises before, eg most recently at http://archives.postgresql.org/pgsql-general/2010-05/msg01126.php regards, tom lane ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Special column trivia 2010-06-06 07:18 Special column trivia Greg Smith <[email protected]> 2010-06-06 10:30 ` Re: Special column trivia Tom Lane <[email protected]> @ 2010-06-10 22:00 ` Bruce Momjian <[email protected]> 0 siblings, 0 replies; 3+ messages in thread From: Bruce Momjian @ 2010-06-10 22:00 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: Greg Smith <[email protected]>; pgsql-docs Tom Lane wrote: > > What got me reading that section was a rather weird documentation > > question/addition from Edmund Horner. He noted that the following works > > on PG8.4 and 9.0: > > > postgres=# select (row(1,2)).name; > > This is the cast-a-composite-type-to-string-type issue that's come up in > several guises before, eg most recently at > http://archives.postgresql.org/pgsql-general/2010-05/msg01126.php Do we need additional documentation? -- Bruce Momjian <[email protected]> http://momjian.us EnterpriseDB http://enterprisedb.com + None of us is going to be here forever. + ^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2010-06-10 22:00 UTC | newest] Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2010-06-06 07:18 Special column trivia Greg Smith <[email protected]> 2010-06-06 10:30 ` Tom Lane <[email protected]> 2010-06-10 22:00 ` Bruce Momjian <[email protected]>
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