On Wednesday 09 June 2004 21:40, Shlomi Fish wrote: > On Wednesday 09 June 2004 16:50, Amir Hardon wrote: > > Hi, > > I'm planning a DB structure for an e-commerce system, and facing some > > question about the DB efficiency that I don't know how to approach. > > > > For example what will be better, storing all items information in one > > table with one column for category, or having a separate items table for > > each category. > > Doesn't having separate tables contradict one of the Relational Database > Model Normalization Rules (can't remember which)? Even if it doesn't, it > seems like a Bad Idea<tm> as far as modularity is concerned. > > For once in an SQL statement, you can't select (AFAIR) a table based on the > value of a select statement. This: > > SELECT * > FROM (SELECT table FROM categories WHERE cat_id = 5) > WHERE item_id = 103
Just for the protocol: this is possible with mssql and oracle: http://www.schemamania.org/jkl/booksonline/SQLBOL70/html/2_005_29.htm > > won't work. (at least I think it won't.) > > Another thing is that you have several tables with the same schema that you > need to update regularly. > > That probably did not answer your question (even tough your guess seems > correct), but it triggered my opinion bit. > > Regards, > > Shlomi Fish > > > My guess is that separate tables will be faster for use but will consume > > more disk space. > > > > Where can I learn about this subject? I guess it also depends on the DB > > backend I'm using, so for this case it is mySQL. > > > > Thanks, > > -Amir. > > > > ================================================================= > > To unsubscribe, send mail to [EMAIL PROTECTED] with > > the word "unsubscribe" in the message body, e.g., run the command > > echo unsubscribe | mail [EMAIL PROTECTED] ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
