Re: PL/pgsql EXECUTE 'SELECT INTO ...'

Tom Lane wrote:
> I have looked a little bit at what it'd take to make SELECT INTO inside
> an EXECUTE work the same as it does in plain plpgsql --- that is, the
> INTO should reference plpgsql variables, not a destination table.
> It looks to me like this is possible but would require some nontrivial
> re-engineering inside plpgsql.  What I'm visualizing is that EXECUTE
> should read its string argument not just as an SPI_exec() string, but
> as an arbitrary plpgsql proc_stmt.  This would offer some interesting
> capabilities, like building a whole FOR-loop for dynamic execution.
> But there are a number of problems to be surmounted, notably arranging
> for the parsetree built by the plpgsql compiler not to be irretrievably
> memory-leaked.  (That ties into something I'd wanted to do anyway,
> which is to have the plpgsql compiler build its trees in a memory
> context associated with the function, not via malloc().)
>
> This does not look like something to be tackling when we're already
> in late beta, unfortunately.  So we have to decide what to do for 7.1.
> If we do nothing now, and then implement this feature in 7.2, we will
> have a backwards compatibility problem: EXECUTE 'SELECT INTO ...'
> will completely change in meaning.
>
> I am inclined to keep our options open by forbidding EXECUTE 'SELECT
> INTO ...' for now.  That's more than a tad annoying, because that leaves
> no useful way to do a dynamically-built SELECT, but if we don't forbid
> it I think we'll regret it later.
   You can do something like
       FOR record_var IN EXECUTE <string-expr> LOOP           ...       END LOOP;
   In this case, the <string-expr> executed over SPI_exec() must   return tuples (0-n). Otherwise you'll get a runtime
error.
   Inside the loop you have access to the tuples via the record.   Is  that  the dynamically-built SELECT capability
you'vebeen   missing?
 
   There's not that much need for mucking with  temp  tables  in   EXECUTE as all this discussion looks to me.


Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#================================================== JanWieck@Yahoo.com #



_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com