CONSTRAINTS

Constraints in Data Bases are used to define and Integrity Constraint, as a rule that restricts the values in a data base.

OR (in other words)

In Oracle CONSTRAINT clause allows you to restrict the date, that is entered into a column to ensure that it is valid or that is meets certain conditions.

Types of Constraints :--

1. NOT NULL Constraint
2. UNIQUE Constraint
3. CHECK Constraint
4. PRIMARY KEY Constraint
5. FOREIGN KEY Constraint

Declaration Style

Column Lever (or) In Line style.

Table Level (or) Out Of Line Style.

Column Level:
         They are declared as part of the definition of an individual column or attribute.
         Usually applied when the constraint is specific to that column only.
Table Level:
        They are declared as part of the table definition.
        Definitely applied when the constraint is applied on combination of columns together.