Re: request for sql3 compliance for the update command - Mailing list pgsql-hackers

With no one replying on how to do correlated subqueries in FROM for
UPDATE, I am adding this to the TODO list:
* Allow UPDATE tab SET ROW (col, ...) = (...) for updating  multiple columns     

Several people indicated they wanted this functionality.  The ROW is SQL
standard, and the column list is an extension.

I do not see any way to allow subqueries without requiring two levels of
parentheses, one for the list, another for the subquery.  ROW should
also be optional.

---------------------------------------------------------------------------

Bruce Momjian wrote:
> 
> While I can see a subquery in UPDATE as working in most cases:
> 
>     UPDATE tab
>     SET col - t.col
>     FROM (SELECT col from xx) AS t
>     WHERE ...
> 
> but I don't see that working for correlated subqueries, where you want
> to set a column based on a value you are updating.  (Many use correlated
> subqueries in UPDATE a lot.) Do FROM subqueries work as correlated
> subqueries?  I can't see how they would because you don't have a row
> being processed at the FROM stage of the query.
> 
> I did look at the SQL99 standards and ROW does appear there:
> 
>          <update statement: positioned> ::=
>               UPDATE <target table>
>                 SET <set clause list>
>                   WHERE CURRENT OF <cursor name>
> 
>          <set clause list> ::=
>               <set clause> [ { <comma> <set clause> }... ]
> 
>          <set clause> ::=
>                 <update target> <equals operator> <update source>
>               | <mutated set clause> <equals operator> <update source>
> 
>          <update target> ::=
>                 <object column>
> -->           | ROW
>               | <object column>
>                   <left bracket or trigraph> <simple value specification> <right bracket or trigraph>
> 
> and later it says:
> 
>             a) If <update target> specifies ROW, then let CL be the set of
>               all columns of T.
> 
> The TODO item would be:
> 
>     Support SQL99 UPDATE SET ROW = () with extension SET ROW (col ...) = ()
> 
> This also gets into that weird Informix syntax where you have to
> double-paren when you want to use a subquery.  Basically, this thing
> keeps getting wierder and wierder.
> 
> ---------------------------------------------------------------------------
> 
> Dave Cramer wrote:
> > Given that the direction of the spec seems to be headed towards the
> > desired syntax, can we put this on the TODO list?
> > 
> > Dave
> > 
> > On Thu, 2003-02-20 at 11:49, Dave Cramer wrote:
> > > Scott,
> > > 
> > > I can't find page 858 in that document, is it the right one? 
> > > 
> > > also the link s/b ?
> > > 
> > > ftp://ftp.sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-01-Framework-2002-01.pdf
> > > 
> > > Dave
> > > On Thu, 2003-02-20 at 11:20, scott.marlowe wrote:
> > > > On Thu, 20 Feb 2003, Tom Lane wrote:
> > > > 
> > > > > Hannu Krosing <hannu@tm.ee> writes:
> > > > > > Are you against it just on grounds of cleanliness and ANSI compliance,
> > > > > > or do you see more serious problems in letting it in ?
> > > > > 
> > > > > At this point it seems there are two different things being tossed
> > > > > about.  I originally understood Dave to be asking for parens to be
> > > > > allowed around individual target column names, which seems a useless
> > > > > frammish to me.  What Bruce has pointed out is that a syntax that lets
> > > > > you assign multiple columns from a single rowsource would be an actual
> > > > > improvement in functionality, or at least in convenience and efficiency.
> > > > > (It would also be a substantial bit of work, which is why I think this
> > > > > isn't what Dave was offering a quick patch to do...)  What I'd like to
> > > > > know right now is which interpretation Informix actually implements.
> > > > > 
> > > > > I don't like adding nonstandard syntaxes that add no functionality ---
> > > > > but if Informix has done what Bruce is talking about, that's a different
> > > > > matter altogether.
> > > > 
> > > > Tom, I was purusing the wild and wonderfully exciting new SQL 
> > > > 
> > > > (found here: 
> > > > ftp://sqlstandards.org/SC32/WG3/Progression_Documents/FCD/4FCD1-01-Framework-2002-01.pdf)
> > > > 
> > > > ANSI TC NCITS H2
> > > > ISO/IEC JTC 1/SC 32/WG 3
> > > > Database
> > > > 
> > > > document to see what it had to say, and on this subject, and it looks like 
> > > > update is going to be supporing this same style we're discussing here.
> > > > 
> > > > Look on or around p. 858 in that doc.)
> > -- 
> > Dave Cramer <dave@fastcrypt.com>
> > Cramer Consulting
> > 
> > 
> 
> -- 
>   Bruce Momjian                        |  http://candle.pha.pa.us
>   pgman@candle.pha.pa.us               |  (610) 359-1001
>   +  If your life is a hard drive,     |  13 Roberts Road
>   +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
> 
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--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073