It's about syntax and clarity, both for the reader and to the query optimizer. The JOIN conditions belong in the ON sub-statement precisely because they are the predicate for the join and serve to grow the data set .. the WHERE query is supposed to specify limiting conditions on that superset.
When I was a newd, I recall sticking my conditions in the WHERE clauses because it seemed to work most of the time, but I would get these occasional glitches where the result did unexpected things. Since I learned the conventions properly, that almost never happens. - md On Fri, Sep 10, 2010 at 9:33 AM, george larson <george.g.lar...@gmail.com> wrote: > Hi all. I've got a greenhorn question but I didn't find the right > keywords to get Google to answer it for me. > > Is it more efficient to put conditions in a JOIN instead of sticking > them all at the end in the WHERE clause, or is that just a matter of > preference? Putting conditions in the JOIN It seems, to me, to at least > make the query easier to read. I was just curious if there were > performance gains as well. > > Example: > > SELECT FROM table1 > JOIN table2 ON this > that > WHERE that = '5'; > > vs > > SELECT FROM table1 > JOIN table2 WHERE this > that AND that = '5'; > > Thanks! > G > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql?unsub=mdyk...@gmail.com > > -- - michael dykman - mdyk...@gmail.com May the Source be with you. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
