Обсуждение: OT - select + must have from - sql standard syntax?
Hi, I don't have a copy of the standard on hand and a collegue is claiming that there must be a from clause in a select query (he is an oracle guy). This doesn't seem to be the case for postgres... does anyone know? Cheers Antoine ps. any one of them will do... -- This is where I should put some witty comment.
On Tue, Jun 13, 2006 at 02:43:45PM +0200, Antoine wrote: > Hi, > I don't have a copy of the standard on hand and a collegue is claiming > that there must be a from clause in a select query (he is an oracle > guy). This doesn't seem to be the case for postgres... does anyone > know? Dunno, but I know that other databases (at least DB2) don't require FROM either. In Oracle, if you want to do something like SELECT now(); you actually have to do SELECT now() FROM dual; where dual is a special, hard-coded table in Oracle that has only one row. Personally, I find their approach to be pretty stupid. -- Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
"Jim C. Nasby" <jnasby@pervasive.com> writes:
> On Tue, Jun 13, 2006 at 02:43:45PM +0200, Antoine wrote:
>> I don't have a copy of the standard on hand and a collegue is claiming
>> that there must be a from clause in a select query (he is an oracle
>> guy). This doesn't seem to be the case for postgres... does anyone
>> know?
> Dunno, but I know that other databases (at least DB2) don't require FROM
> either.
The spec does require a FROM clause in SELECT (at least as of SQL99, did
not check SQL2003). However, it's clearly mighty useful to allow FROM
to be omitted for simple compute-this-scalar-result problems. You
should respond to the Oracle guy that "SELECT whatever FROM dual" is not
in the standard either (certainly the spec does not mention any such
table). And in any case an Oracle fanboy has got *no* leg to stand on
when griping about proprietary extensions to the spec.
regards, tom lane
Tom Lane <tgl@sss.pgh.pa.us> writes: > The spec does require a FROM clause in SELECT (at least as of SQL99, did > not check SQL2003). However, it's clearly mighty useful to allow FROM > to be omitted for simple compute-this-scalar-result problems. You > should respond to the Oracle guy that "SELECT whatever FROM dual" is not > in the standard either (certainly the spec does not mention any such > table). Well you could always create a "dual", it was always just a regular table. We used to joke about what would happen to Oracle if you inserted an extra row in it... Oracle used to always require FROM, if it has stopped requiring it then that's new. I had heard it had special-cased dual in later versions to avoid the table access overhead, I suspect these two changes are related. -- greg
> > The spec does require a FROM clause in SELECT (at least as of SQL99, did > > not check SQL2003). However, it's clearly mighty useful to allow FROM > > to be omitted for simple compute-this-scalar-result problems. You > > should respond to the Oracle guy that "SELECT whatever FROM dual" is not > > in the standard either (certainly the spec does not mention any such > > table). Thanks for your answers guys. I was pretty sure DUAL wasn't in the standard (never seen it outside an oracle context) but wasn't at all sure about the FROM. Cheers Antoine ps. shame the standard isn't "freely" consultable to save you guys silly OT questions! -- This is where I should put some witty comment.
> -----Original Message----- > From: pgsql-performance-owner@postgresql.org > [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of > Greg Stark > Sent: Tuesday, June 13, 2006 11:16 PM > Subject: Re: [PERFORM] OT - select + must have from - sql > standard syntax? [SNIP] > > Well you could always create a "dual", it was always just a > regular table. We > used to joke about what would happen to Oracle if you > inserted an extra row in > it... I've never used Oracle, so I don't understand why its called dual when it only has one row? Shouldn't it be called single? :\ Dave
Antoine <melser.anton@gmail.com> writes:
> ps. shame the standard isn't "freely" consultable to save you guys
> silly OT questions!
You can get free "draft" versions that are close-enough-to-final to be
perfectly usable. See our developers' FAQ for some links. I like the
drafts partly because they're plain ASCII, and so far easier to search
than PDFs ...
regards, tom lane
> You can get free "draft" versions that are close-enough-to-final to be > perfectly usable. See our developers' FAQ for some links. I like the > drafts partly because they're plain ASCII, and so far easier to search > than PDFs ... Great to know - thanks! Cheers Antoine -- This is where I should put some witty comment.