Re: discussion forum from j. meloni's book

* Thus wrote Anthony Ritter (tony@gonefishingguideservice.com): > Jennifer Goodie" <goodie@apollointeractive.com> writes: > > > You didn't switch the aliases around, you just switched the join order. > > This will provide unexpected results. In order to understand it, you > should > > read up on left joins. > > http://www.mysql.com/doc/en/JOIN.html > ............................ > Thank you. But... > > // the query > > $verify = "select ft.topic_id, ft.topic_title from forum_posts as fp left > join forum_topics as ft on fp.topic_id = ft.topic_id where fp.post_id = > $_GET[post_id]"; > ........................... > > My question: why - or how can - the columns ft.topic_id and ft.topic_title > come from the table forum_posts? The dont. ft is aliased to forum_topic it has nothing to do with form_posts. > > > When I change the following to read: > > $verify = "select ft.topic_id, ft.topic_title from forum_topics as ft left > join forum_posts as fp on fp.topic_id = ft.topic_id where fp.post_id = > $_GET[post_id]"; > > It works fine. > > /*Roughly translated: Select the column ft.topic_id along with the column > ft.topic_title from the table called forum_topics which we'll call ft. Then > join the table called forum_topics onto the table called forum_posts and > match the records where topic_id corresponds in both tables along with > post_id corresponds in both tables.*/ There are a lot of thing wrong with your summary. What you are doing is selecting *all* rows from ft. include any rows from fp that have the same topic_id where fp has a post_id of the $_GET variable. This query makes absolutly no sense, in real world application. btw, this topic is completely off-topic, you might be able to get better assistance with this query on the mysql list. Curt -- "I used to think I was indecisive, but now I'm not so sure."