Re: Precedence of Postfix operators

Thanks Tom, for the explanation.

Gokul.

On Sun, Feb 7, 2010 at 10:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> writes:
> > Is there any reason why we have given lesser precedence for postfix
> > operator compared to multiplication/division? Usually postfix operators
> have
> > more precedence than the binary operations. Is this some kind of work
> around
> > to provide user-defined operators? Can someone help me understand this?
>
> A bit of poking in the CVS logs for gram.y reveals
>
> 2001-01-23 17:39 tgl
>
> * src/backend/parser/gram.y: Give 'a_expr ::= a_expr Op' production
> a slightly lower precedence than Op, so that the sequence 'a_expr
> Op Op a_expr' will be parsed as a_expr Op (Op a_expr) not (a_expr
> Op) Op a_expr as formerly. In other words, prefer treating
> user-defined operators as prefix operators to treating them as
> postfix operators, when there is an ambiguity. Also clean up a
> couple of other infelicities in production priority assignment ---
> for example, BETWEEN wasn't being given the intended priority, but
> that of AND.
>
> There are several other nasty things that we've had to do in order to
> keep supporting postfix operators at all. I thibk most people view them
> as a legacy feature best avoided.
>
> regards, tom lane
>