Yeah, i was wondering whether i needed that field as i couldn't see how i'd use it. I'll go ahead and delete it.
Thanks, Stuart On 15 Jul 2005, at 00:52, Dave Watts wrote: >> I want to add a row in a join table which i don't want to be >> duplicated ever. >> >> So i have my tableID, table1ID, table2ID - if table1ID = 24 >> and table2ID = 35 i don't want there to ever be a reoccurence of >> them. I guess i have to set both of those fields (table1ID, table2ID) >> to primary keys, but how can i do that? Do i do it in ms-sql or via >> Coldfusion somehow? >> > > As a bunch of people have already mentioned, you can create > compound keys > within your database. A compound key consists of more than one > field. If you > go that route, you really don't need the "tableID" field any more > (assuming > that field is currently being used as your primary key) - you can > just make > the combination of table1ID and table2ID your primary key. > > One disadvantage of this is that, if you have other tables which are > dependent upon this one, those tables will need to contain both > fields for > use as a foreign key. However, in all likelihood you don't have any > other > tables which are dependent upon this one, but rather this table is > dependent > upon two other tables - this kind of table is often called a > linking or > intersection table. The "middle" table in a many-to-many relationship > typically follows this pattern. > > Another disadvantage of this is that you won't be able to store > historical > relationship data - either a relationship exists now, or it > doesn't. If you > do want to store historical data, you'd need to keep the current > "tableID" > as your primary key, or add a third field to your two-field primary > key - > the value of that third field would have to be different for any > two rows > that have the same values for the other two fields. > > >> If i do it via MS-SQL then won't it pop an error up in the code if >> it happens? >> > > Yes, like any other invalid query you might run. It's up to you to > catch and > resolve those errors appropriately within your code. > > Dave Watts, CTO, Fig Leaf Software > http://www.figleaf.com/ > > Fig Leaf Software provides the highest caliber vendor-authorized > instruction at our training centers in Washington DC, Atlanta, > Chicago, Baltimore, Northern Virginia, or on-site at your location. > Visit http://training.figleaf.com/ for more information! > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Discover CFTicket - The leading ColdFusion Help Desk and Trouble Ticket application http://www.houseoffusion.com/banners/view.cfm?bannerid=48 Message: http://www.houseoffusion.com/lists.cfm/link=i:4:211943 Archives: http://www.houseoffusion.com/cf_lists/threads.cfm/4 Subscription: http://www.houseoffusion.com/lists.cfm/link=s:4 Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=11502.10531.4 Donations & Support: http://www.houseoffusion.com/tiny.cfm/54
