Ok. it might be, but i thougt that if i have a table with all users in and a table with all messages in and i want 10 users to se 1 message and i do the relation with foreign-key mapping i would insert 10 messages in the messages table that are exactly the same but with a diferent userkey in the userkey field.
if i use a relation table i would insert 1 messsage in the message table and 10 rows in the relation table. that only contains the key to the 10 users and 1 message, then i would only fill message text in one row so it wouldnt fill the database with duplicates of the message. On Thu, 2003-10-02 at 15:06, Daniel L�pez wrote: > Hi David, > That's exactly what indexes are for, and they are created/mantained > "automatically" by your database. In fact, if you created such a table > you would be duplicating information, as you would be repeating the > original table key in n rows of your "relationship table" AND repeating > the other key. It would be like an N-M relationship. > Graphically, something like... ( Table A and Table B, 1-N from A to B): > Table A > ------- > A1, AData_1, ... > A2, AData_2, ... > > Table B > ------- > B1, BData_1,..., A1 > B2, BData_2,..., A1 > B3, BData_3,..., A1 > B4, BData_4,..., A2 > > with an extra table... > > Table A > ------- > A1, AData_1, ... > A2, AData_2, ... > > Table B > ------- > B1, BData_1,... > B2, BData_2,... > B3, BData_3,... > B4, BData_4,... > > Table A_B > ------- > B1, A1 > B2, A1 > B3, A1 > B4, A2 > > If you don't have any index on table B using the foreign key of table A, > you might get some performance improvement but it is in this case where > one would have "unnecessary data". I always recommend and use indexes > and just two tables but... > Regards, > D. > > > David Nielsen escribi�: > > > As i undestand it: > > If I do it bidirectional in my example i would insert a row pr. > > mailmessage for each user i sent it to, it would gime a lot of similar > > mailmessages, with just the toUsers field changed, if you have a > > unidirectional relation with a relation table you would only have one > > row in mailmessages with the actual message and a lot of foreign key in > > the relation table thar points at this one message. > > so you would not have a lot of unnessesary data, and the database woulnd > > grow as big. > > Im not a pro database, but i would think it would give me some > > performance, if i just have a relation table which only contains keys to > > my actual tables. > > > > > > Regards, David > > > > On Thu, 2003-10-02 at 12:30, Daniel L�pez wrote: > > > >>Hi, > >>Do you really need an extra table when creating a unidirectional 1-n > >>relationship? I've always used bidirectional relationships so I've never > >>tried, but I don't see the reason why unidirectional ones would require > >>such an extra table. May be I did not understand the statement below. > >>Cheers, > >>D. > >> > >>Edward Kenworthy escribi�: > >> > >>>This is a unidirectional 1:m so yes you do need a relationship table. > >> > >>... //snipped > > > > > > ------------------------------------------------------- > This sf.net email is sponsored by:ThinkGeek > Welcome to geek heaven. > http://thinkgeek.com/sf > _______________________________________________ > xdoclet-user mailing list > [EMAIL PROTECTED] > https://lists.sourceforge.net/lists/listinfo/xdoclet-user > ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ xdoclet-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/xdoclet-user
