Re: Variable LIMIT and OFFSET in SELECTs

On Fri, Nov 16, 2007 at 01:38:30AM -0500, Tom Lane wrote:
> Sam Mason <sam(at)samason(dot)me(dot)uk> writes:
> > wow, that's kind of fun isn't it. I only thought you could put a
> > constant in there. Maybe I should have had a look in the grammar/tested
> > it first!
>
> IIRC, it used to be restricted to a constant, a few revisions back.
> In current releases the only restriction that stems from laziness is
> not allowing a sub-select. (If anyone were to put forward a serious
> use-case, we'd probably go fix that.)

I'm amazed it supports anything more than a constant. The values are
almost always going to come from external code, so there doesn't seem
much point in doing anything else.

I suppose with all the expression evaluation code already in PG,
supporting what it currently does isn't hard.

> The OP's complaint is that we don't allow a variable of the query's own
> level, but AFAICT he's still not grasped the point that that leads to an
> indeterminate limit value ...

Being too close to a problem makes it very easy to forget about the
general case. I probably do this far too often myself!

Sam