A primary key is a field used to uniquely identify every record in the database. Sometime primary keys are obvious, for example a car license plate could be used to uniquely identify cars. Often, ...

I'm adding a table and subclass table to my DB. (Subclass table = table where the primary key joins to the primary key of another table, to give extra row information to some subset of the rows.

There are two categories of integrity constraints: General constraints, which allow you to restrict the data values that are accepted for the variables in a single data file, such as requiring that ...