CHECK constraint on date of birth?

Question

I am creating my employee table in Oracle and for emp_date I would like to make it so the date of birth is not way back in the past and can not be set in the future?

Answer 1

Check constraints must be deterministic. That is, a particular row must always satisfy the constraint or it must always fail to satisfy the constraint. But SYSDATE is inherently non-deterministic since the returned value is constantly changing. Thus, you cannot define a CHECK constraint that calls SYSDATE or any other user-defined function.

If you try to reference SYSDATE in the constraint definition, you'll get an error

SQL> ed
Wrote file afiedt.buf

  1  create table t(
  2      birth_date date check( birth_date between date '1900-01-01' and
  3                                                sysdate )
  4* )
SQL> /
                                              sysdate )
                                              *
ERROR at line 3:
ORA-02436: date or system variable wrongly specified in CHECK constraint

You could create a CHECK constraint where both the minimum and maximum date were hard-coded but that would not be particularly practical since you'd have to constantly drop and recreate the constraint.

SQL> ed
Wrote file afiedt.buf

  1   create table t(
  2       birth_date date check( birth_date between date '1900-01-01' and
  3                                                 date '2011-12-08' )
  4*  )
SQL> /

Table created.

The practical way to enforce this sort of requirement would be to create a trigger on the table

CREATE OR REPLACE TRIGGER check_birth_date
  BEFORE INSERT OR UPDATE ON employee
  FOR EACH ROW
BEGIN
  IF( :new.emp_dob < date '1900-01-01' or 
      :new.emp_dob > sysdate )
  THEN
    RAISE_APPLICATION_ERROR( 
      -20001, 
      'EMployee date of birth must be later than Jan 1, 1900 and earlier than today' );
  END IF;
END;