On 28/02/2008, Nigel Metheringham <[EMAIL PROTECTED]> wrote: > > > On 28 Feb 2008, at 09:51, Dermot wrote: > > 1) I have been using the MySQL workbench tool to try and make a ER > > diagram of a database. The community edition doesn't allow printing > > but is excellent in every other way. Could anyone recommend a > > similar tool? I hear Dia is a good OS tool. > > > Given a db or DBIC description, there are some tools in > SQL::Translator to spit out ER diagrams. > > > > 2) I posted a query about the Catalyst tutorials and that fact that > > the used a join table to show many to many relationships between > > authors and books. Is this type of table what is termed a view? Or > > am I still not getting it :-( > > > Not a view - those are the table like things you can produce with > CREATE VIEW ... > > The problem is that you can do a many-to-one or one-to-many > relationship by having the many item contain a foreign key to the one > item. However there is no such neat method to do a many-to-many > relationship, so you have to break it down to be a pair of > relationships - a many-to-one-to-many combination with the link table > in the middle consisting of foreign keys to the other pair of tables. > > As an example, for a theatre event (as in show) handling db I have, > each show has 0 or more ticket agencies selling tickets. The ticket > agencies are re-used for many events (so a place in town will sell > tickets for many events). > > Hence I have an "event" table > and a "ticket_agent" table > and a "event_ticket_agent" table - this one purely consists of 2 > fields - the event id and the ticket_agent id, and links the pair. > > I refer to that as a link table, but I am a sysadmin rather than a DB > expert :-) > > Hope that helps a bit. > > Nigel. >
That does Nigel thanx. In the DB I am trying to design I can see lots of 1:M relationships but I can't see a case for using a join table. That's leading to me thinking that I am doing something wrong. MySQL workbench doesn't appear to be on sale retail yet. Having used it I would like to have a copy of the standard edition. I'm off to cpan the as per Peter post and check out SQL::Translator. Thanx again. Dp.
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