At 01:47 AM 1/7/00 +0200, Hannu Krosing wrote:
>IMHO the ANSI standard (as anything designed by a committee) is not always
the
>best
>way to do things.
Well, generally standards committees don't design features. They're
usually designed by one or two people, then submitted to the committee
for discussion and eventual adoption or rejection.
My understanding from reading Date is that one reason for not adopting
the common vendor hacks for outer joins is that outer joins aren't
associative and the result of complicated expressions in some cases
will depend on the order in which the RDBMS' optimizer chooses to
execute them.
Putting on my compiler-writer hat, I can see where having joins
explicitly declared in the "from" clauses rather than derived from
an analysis of the "from" and "where" clauses might well simplify
the development of a new SQL 92 RDBMS if one were to start from
scratch. It's cleaner, IMO. This doesn't apply to Postgres,
since the outer joins are being shoe-horned into existing data
structures.
Of course, I speak as someone without
a lot of experience writing Oracle or Informix SQL. If you're used
to Oracle, then it's not surprising you find its means of specifying
an outer join the most natural and easiest to understand...
- Don Baccus, Portland OR <dhogaza@pacifier.com> Nature photos, on-line guides, Pacific Northwest Rare Bird Alert
Serviceand other goodies at http://donb.photo.net.