primary key is a candidate key to uniquely identify each row in a table. A unique key or primary key comprises a single column or set of columns. No two distinct rows in a table can have the same value (or combination of values) in those columns. Depending on its design, a table may have arbitrarily many unique keys but at most one primary key.
a compound key is a key that consists of 2 or more attributes that uniquely identify an entity occurrence. On Sat, Jan 2, 2010 at 10:05 PM, Victor Subervi <victorsube...@gmail.com>wrote: > On Sat, Jan 2, 2010 at 11:20 AM, Arthur Fuller <fuller.art...@gmail.com > >wrote: > > > Hi Victor. > > > > I think that the first thing you need to consider is whether a product > can > > be in more than one package, and second is whether a package can be in > > another package. Also, I don't know why you need to auto-generate in > either > > case. It's pretty simple DDL. > > > > Case 1: product can only be in one package: > > > > 1. Add a Packages table with columns PackageID and PackageName and > probably > > PackagePrice. > > 2. Add a PackageID column to the Products table and make it a foreign key > > referencing Packages. > > > > Case 2: product can be in multiple packages: > > 1. Same as above. > > 2. Create a ProductPackages table that contains PackageID and ProductID, > > both as foreign keys into Products and Packages. > > 3. Decide whether you want a compund PK on this new table, or you want > > instead an auto-increment column that would be the PK. (There are > > differences of opinion on this one, so I'm leaving it alone; I don't want > to > > start a religious war :) > > > > Thanks! That's reversing my thinking! I hadn't considered working the other > direction. What is a PK and a compound PK? > TIA, > V > -- Best Regards, Prabhat Kumar MySQL DBA Datavail-India Mumbai Mobile : 91-9987681929 www.datavail.com My Blog: http://adminlinux.blogspot.com My LinkedIn: http://www.linkedin.com/in/profileprabhat
