OK... I actually looked in the manual this time to get some
clarification - http://dev.mysql.com/doc/refman/5.0/en/join.html:
"INNER JOIN and , (comma) are semantically equivalent in the absence
of a join condition: both produce a Cartesian product between the
specified tables (that is, each and every row in the first table is
joined to each and every row in the second table)."
"Generally, you should use the ON clause for conditions that specify
how to join tables, and the WHERE clause to restrict which rows you
want in the result set."
For your question Adrian... I can't find any information backing this
up... but I'm pretty sure that INNER JOIN...ON and JOIN...ON are
synonymous. I did find this "In MySQL, CROSS JOIN is a syntactic
equivalent to INNER JOIN (they can replace each other). In standard
SQL, they are not equivalent. INNER JOIN is used with an ON clause,
CROSS JOIN is used otherwise." In the join syntax definition they
show "table_reference [INNER | CROSS] JOIN table_factor
[join_condition] " -- and that's why I think they're synonymous -- at
least in MySQL.
I also found the old conversation... now I remember what it was
about. I saw an article on contentwithstyle.co.uk saying that INNER
JOINs were faster and posted it to the list - http://lists.nyphp.org/
pipermail/mysql/2006-July/000162.html Ellen Coen responded that she
didn't know about the validity of it, but felt that the more
specific, the better. That sounded good to me. http://
lists.nyphp.org/pipermail/mysql/2006-July/000163.html So I guess the
consensus was just between the two of us... if anyone else can come
up with a good argument or knows anything more about what the
database does behind the scenes, feel free to chime in.
Thanks,
Rob
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