Defining Constraints

• Column-level constraint:
  

  
  
  CREATE TABLE employees(
  
     employee_id   NUMBER(6)
  
        CONSTRAINT emp_emp_id_pk PRIMARY KEY,
  
     first_name    VARCHAR2(20),
  
     ...);

  

  
  
• Table-level constraint:
  

  
  
  CREATE TABLE employees(
  
    employee_id   NUMBER(6),
  
    first_name    VARCHAR2(20),
  
    ...
  
    job_id        VARCHAR2(10) NOT NULL,
  
    CONSTRAINT    emp_emp_id_pk
  
      PRIMARY_KEY(EMPLOYEE_ID));