Re: Gram.y patches for better parenthesis handling.

"Kevin O'Gorman" <kogorman@pacbell.net> writes:
> 2) It does NOT preserve the odd syntax I found when I started looking
> at this, where a SELECT statement could begin with parentheses.  Thus,
>   (SELECT a from foo) order by a;
> fails.

Um, as a general rule that's not an acceptable limitation.  Consider
(SELECT foo EXCEPT SELECT bar) INTERSECT SELECT baz;

Without parens this will mean something quite different, since
INTERSECT has higher precedence than EXCEPT.

Also, a leading paren is clearly legal according to SQL92 --- trace
for example the productions        <direct select statement: multiple rows>        <query expression>        <non-join
queryexpression>        <non-join query term>        <non-join query primary> ::=             <left paren> <non-join
queryexpression> <right paren>
 

(UNION/EXCEPT structures are <non-join query expression> in this
hierarchy.)

The reason that making this grammar yacc-compatible is so hard is
precisely that leading parens must sometimes be part of the SELECT
structure, whereas extraneous parens need to be kept out of it.
        regards, tom lane