Обсуждение: " ::= " grammar rule not accepted by Postgres

<p><font face="sans-serif" size="2">This expression is (I think) a well-formed query, but is rejected by Postgresql 8.4
(tis a table name).</font><br /><br /><font face="sans-serif" size="2"> t t1 NATURAL JOIN t t2;</font><br /><br /><font
face="sans-serif"size="2">Here is the relevant parts of grammar (with some optional elements omitted for simplicity):
</font><br/><br /><font face="sans-serif" size="2"> <query expression> ::= <query expression
body></font><br/><br /><font face="sans-serif" size="2"> <query expression body> ::= <joined
table></font><br/><br /><font face="sans-serif" size="2"> <joined table> ::= <natural join></font><br
/><br/><font face="sans-serif" size="2"> <natural join> ::= <table reference> NATURAL JOIN <table
primary></font><br/><br /><font face="sans-serif" size="2"> <table reference> ::= <table
primary></font><br/><br /><font face="sans-serif" size="2"> <table primary> ::= <table or query name> [
<correlationname> ]</font><br /><br /><font face="sans-serif" size="2"> <table or query name> ::= <table
name></font><br/><br /><font face="sans-serif" size="2">Nor is this use of <joined table> accepted in the
<queryexpression> form of a <with list element>:</font><br /><br /><font face="sans-serif" size="2"> WITH
twAS ( t t1 NATURAL JOIN t t2 ) TABLE tw; </font><br /><br /><font face="sans-serif" size="2">This leads me to believe
thatthe unrecognized grammar rule (in SQL99 standard terms) is</font><br /><br /><font face="sans-serif" size="2">
<queryexpression body> ::= <joined table></font><br /><br /><font face="sans-serif" size="2">There are, of
course,other ways to express the operation, including</font><br /><font face="sans-serif" size="2"> SELECT * FROM (t t1
NATURALJOIN t t2);</font><br /><font face="sans-serif" size="2">But I am curious why the first expression is not
accepted,besides the immediately obvious "it's not in the Postgres version of the SQL grammar."</font><br /><br /><font
face="sans-serif"size="2">Clem Dickey</font> 

Clem Dickey <dickeycl@us.ibm.com> writes:
> This expression is (I think) a well-formed query, but is rejected by
> Postgresql 8.4 (t is a table name).

>   t t1 NATURAL JOIN t t2;

Hmm ... I think you are looking at SQL92 or SQL99.  The later versions
of the spec don't seem to permit <joined table> to be used that way.
In particular, in SQL:2003 and SQL:2007 I don't see any derivation path
from <query expression> to <joined table>.  So while we possibly could
support this, it's legacy syntax, and I doubt there's enough interest to
bother.

[ digs a bit more... ]  Ah, here we are: Annex E of SQL:2003 calls out
various incompatibilities from SQL:99, notably
6) In ISO/IEC 9075-2:1999, a <query expression body>, <queryterm>, or <query primary> could consist of a <joinedtable>.
Noneof those three elements can consist of a <joinedtable> in this edition of ISO/IEC 9075.
 
        regards, tom lane

On 06/15/2011 10:59 PM, Tom Lane wrote:
> Clem Dickey<dickeycl@us.ibm.com>  writes:
>> This expression is (I think) a well-formed query, but is rejected by
>> Postgresql 8.4 (t is a table name).
>
>>    t t1 NATURAL JOIN t t2;
>
> Hmm ... I think you are looking at SQL92 or SQL99.

> [ digs a bit more... ]  Ah, here we are: Annex E of SQL:2003 calls out
> various incompatibilities from SQL:99, notably
>
>     6) In ISO/IEC 9075-2:1999, a<query expression body>,<query
>     term>, or<query primary>  could consist of a<joined
>     table>. None of those three elements can consist of a<joined
>     table>  in this edition of ISO/IEC 9075.

Thanks for the research. I was indeed reading from SQL99, which was 
current the last time I used SQL. I'll have to spring for a newer 
standard (or the equivalent).