Re: BUG #3822: Nonstandard precedence for comparison operators

>>> On Thu, Dec 27, 2007 at  4:22 PM, in message <21242.1198794130@sss.pgh.=
pa.us>,
Tom Lane <tgl@sss.pgh.pa.us> wrote:=20
> "Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:

> To the extent that you do believe the spec, there are more problems with
> our precedence rules than just where <=3D fits --- it looks to me like IS
> [NOT] NULL is at the wrong precedence, too.  And then there's the whole
> question of associativity.
=20
Well, surely, the fact that there is more than one problem isn't,
by itself, an argument not to fix any of them.
=20
>> It seems to call for the same phased approach as the standard
>> conforming string literals, with GUCs to control warnings for problem
>> constructs and legacy versus standard runtime behavior.
>=20
> Good luck implementing that --- the precedence is hard-wired into the
> bison grammar rules.  There are also extremely good reasons for not
> having GUC variables that affect parsing behavior.
=20
But we have done so before, in the interests of converging on the
standard.
=20
> Given that it's been this way for ten years and no one has complained
> before, I'm disinclined to change it, and even more disinclined to
> invest the effort that would be involved in letting the behavior vary
> at runtime.
=20
That's a fair point.  It's very unlikely to bite an existing
PostgreSQL user very hard.  The pain could come in migrating a large
set of complex queries from another DBMS.  I don't recall seeing any
migration document to help people identify these issues up front,
but we should probably have one (if we don't) and this should
probably be mentioned.
=20
Based on this discussion, I'll remind our staff to be generous in
the use of parentheses when doing ad hoc queries.
=20
-Kevin
=20