Re: unary operators, precedence, grouping

"woger151" <woger151(at)jqpx37(dot)cotse(dot)net> writes:
> Why wouldn't <~~(item_1) + <~~(item_2) be parsed as (<~~(item_1)) +
> (<~~(item_2))?

Because it's parsed as
<~~ ( (item_1) + ( <~~ (item_2) ) )
"+" binds more tightly than any non-built-in operator, per the
precedence chart in the manual:
http://www.postgresql.org/docs/8.2/static/sql-syntax-lexical.html#SQL-PRECEDENCE
so this interpretation is preferred over the alternative
( <~~ (item_1) ) + ( <~~ (item_2) )
Those are the only two possibilities without getting into right-unary
operators, which the parser is generally designed not to do if it can
avoid it.

regards, tom lane