On febr. 2, 15:15, lew...@xxxxxxxxxxxxxx (Lewis Cunningham) wrote: > --- vladimir konrad <v...@xxxxxxxxxxxxx> wrote: > > > I think that I understand basic relational theory but then I had an > > idea. > > Basically, instead of adding field to a table every time there is a > > need for it, have a table split in two: one holds identity (id) and > > one holds the attributes (linked to this id). > > Basically, if in the future user decides that the subject should > > have a new attribute, he can simply add "attribute definition" and > > attribute_definition_set (if any) and the application would handle > > Basically, you would be creating your own data dictionary (i.e. > system catalog) on top of the db data dictionary. The database > already comes with a way to easily add columns: ddl. I have seen > newbie database designers reinvent this method a hundred times. The > performance hits and complexity of querying data would far out weigh > any perceived maintenance gain. > > My .02. > > LewisC > > Lewis R Cunningham > > An Expert's Guide to Oracle Technologyhttp://blogs.ittoolbox.com/oracle/guide/ > > LewisC's Random Thoughtshttp://lewiscsrandomthoughts.blogspot.com/ > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match I always thought that having nullable columns in a table is a Bad Thing (http://technet.microsoft.com/en-us/library/ms191178.aspx) and shows that you try to put different type of entities into the same table - having 90 in a column ... brrrrr. I think its much better to avoid it whenever you have the info but when you don't you just have to use the EAV model. E.g. If I knew what info I wanted to store on a person I could create columns for that, but since in our application users create the questionnaires that is used to store info on persons I see little choice - I must have a subjectID, questionID, value table. SWK SWK ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your message can get through to the mailing list cleanly
