On Sun, Feb 7, 2010 at 10:14 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Gokulakannan Somasundaram <gokul007@gmail.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.
