Re: [PATCH] Simplify EXISTS subqueries containing LIMIT

Hi

Thanks for taking a look.

On Sun, Oct 19, 2014 at 1:22 PM, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> the argument for this would
> have been much stronger if anti join support had just been added last week.
> It's been quite a few years now and the argument for this must be getting
> weaker with every release.

I see your point, but I would put it another way: we've had this for a
few years, but people haven't learned and are *still* using LIMIT 1.

----
Actually I thought of a cleverer approach to solve this, that doesn't
require calling eval_const_expressions and works with any expression.

Given query:
EXISTS (SELECT ... WHERE foo LIMIT any_expr())
we could turn it into the almost-equivalent form:
EXISTS (SELECT ... WHERE foo AND any_expr() > 0)

The only problem is that we'd no longer be able to throw an error for
negative values and that seems like a deal-breaker.

Regards,
Marti