Re: [HACKERS] Add hint for function named "is"

On Mon, Apr 30, 2018 at 2:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Not *nearly* as much as I'd object to mostly-breaking postfix operators.
> Now admittedly, if the Berkeley guys had never put those in, nobody
> would miss them. But they're there, and I'm afraid that users are
> likely depending on them. Neither of your suggestions above would be
> any less damaging to such users than removing the feature altogether.

Well, that sounds different than what you said upthread in August of 2016:

tgl> Agreed, if postfix operators were the only thing standing between us and
tgl> fixing that, it would be a pretty strong argument for removing them.

I agree that there could be some people using numeric_fac, the only
postfix operator we ship. Probably not many, since it's an
inefficient implementation of an operation that overflows for all but
a few tens of thousands of possible input values, but some. But we
could keep that operator working without supporting the facility in
general. Do we have any evidence at all that anybody has got a
user-defined postfix operator out there? I'm reluctant to keep a
feature that's blocking such an important improvement unless we can
come up with some real examples of it being used. I've never run
across it, and a Google search didn't turn up any examples of anybody
else using it, either.

The basic problem here, for those following along from home, is that
if we allow "SELECT h hour FROM tab" to mean select column h with
column alias hour, then "SELECT hour + 24 * day" becomes ambiguous in
the face of postfix operators: it could either mean what it obviously
is intended to mean, or it could mean that you should look for a
postfix * operator, apply that to 24, add hour to the result, and then
call the resulting column "day". This is less obviously insane when
you use a differently-named operator and columns -- who knows which
way "SELECT thunk + squidge!!! snarkke FROM frobnitz" is intended to
be interpreted. But I'm just a bit doubtful that anyone is going to
stop using PostgreSQL because we take away their ability to make !!! a
postfix operator, whereas I think the inability to alias columns
without using AS when the column label happens to be a keyword IS a
problem for adoption.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company