> 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 > > I use it in the same manner : at the time of recording, I just know one kind of entity (words) with a value as varchar. Maybe better with xml, but i use for long time to do the following job with SQL. ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
