Creating business rules and constraints on your SQL tables is actually a part of the database design phase. We treat it as a separate topic as these rules can be added later instead of creating them at the same time as the tables. This is really a good thing as none of us can think of everything during the design phase.
There are two kinds of business rules and constraints – those that perform referential integrity of the tables and those that apply actual business rules. These two kinds of constraints are ...
