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've been
missing?

There's not that much need for mucking with temp tables in
EXECUTE as all this discussion looks to me.

Jan

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