Åsmund Kveim Lie <asmundkl@skipthis.ifi.uio.no> writes:
> SELECT * FROM a,b NATURAL JOIN c;
This parses as
select * from a, (b natural join c)
> SELECT * FROM a CROSS JOIN b NATURAL JOIN c;
This parses as
select * from (a cross join b) natural join c
> These two example queries should give the same result. In the first query, it
> seems like itâs doing the natural join between b and c, and then does
> the Cartesian product on that result with a. On the second query, it does as
> we assume it should, namely does the Cartesian product first.
>
> Is this the correct behavior?
yes
You can put parentheses to change the explicit joins like
select * from a cross join (b natural join c);
But the implicit join is harder to fix. I think you either need to use an
explicit join like above or a subquery like
select * from (select * from a,b) as ab natural join c
I tend to find it's easier to stick to all explicit or all implicit joins and
not mix them. Personally I like explicit joins for aesthetic reasons
especially in 7.4 where they get optimized as well as implicit joins.
--
greg
