Re: Variable LIMIT and OFFSET in SELECTs

Reg Me Please wrote:
> Sorry but I don't understand.
>
> Either the LIMIT and OFFSET are to be definitely CONSTANT or not.

They must be constant during the execution of the query.

> In the SQL function body the LIMIT and the OFFSET *are definitely not*
> CONSTANT. And the planner can do its job at best as usual.

Well, they're constant during one execution of the query, but I grant
you the planner doesn't know what values they will have.

> As Sam says I should be able to "put an IMMUTABLE expression into a LIMIT or
> OFFSET". And under some circumstances (SQL function body) it's true even with
> VARIABLE expressions like function call arguments.

And you can.

CREATE FUNCTION limfunc() RETURNS integer AS 'SELECT 2' LANGUAGE SQL
IMMUTABLE;

SELECT * FROM fit LIMIT limfunc();
  a | b
---+----
  1 | 43
  2 | 43
(2 rows)


> In my opinion I would say it's more a problem with the syntax checker that
> with the planner ("semantics" in my lingo). But I could be wrong.

Well, what it won't let you do is have a subquery in the LIMIT clause.
That's probably due to a combination of:
1. The spec probably says something about it
2. There is an obvious approach involving functions/prepared queries
3. You're the first person to have asked for it.

Now if you can get a couple of hundred to join you at #3, you might have
a feature request :-)

--
   Richard Huxton
   Archonet Ltd