Re: Gram.y patches for better parenthesis handling.

"Kevin O'Gorman" <kogorman(at)pacbell(dot)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 query expression>
<non-join query term>
<non-join query primary> ::=
<left paren> <non-join query expression> <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