Hi Jieh Chia, When identifying primary keys, you may encounter a situation where there are no natural primary keys, or the ones available aren't suitable, so you can essentially make a surrogate key (which is what you're suggesting). A surrogate key is a primary key created by the database designer to simplify the identification of entity instances. Surrogate keys are useful in the following situations: When there is no natural key. When the selected candidate key has embedded semantic contents (or is unusable due to privacy concerns). When the selected candidate key is too long. I hope this helps. Thanks, Adam. "Jieh Chia" <24*1*5*4@s*u*e*t*u*a*e*u*a*> wrote: