Constraints

- NOT NULL
- UNIQUE
- PRIMARY KEY
- FOREIGN KEY
- CHECK

• You can name a constraint, or the Oracle server automatically generates a name by using the SYS_Cn
  
• All constraints are stored in the data dictionary.
  
• SYS_Cn  n is an integer so that the constraint name is unique.
  
• Define a constraint at the column or table level.
  

* Syntax



CREATE TABLE [schema.]table

(column datatype [DEFAULT expr]

[column_constraint],

...

[table_constraint][,...]);



* Column level constraint:

column [CONSTRAINT constraint_name] constraint_type,



*Table level constraint:

column, ...

[CONSTRAINT constraint_name] constraint_type

(column, ... ),

• NOT NULL constraints must be defined at the column level.