Tip

Check digit function

It is a good idea to have a check digit in ID columns, especially if values are entered manually. Here is a check function to use:

CREATE OR REPLACE  FUNCTION add_check_digit( in_val IN NUMBER ) RETURN NUMBER AS
   c_in_val VARCHAR2(100);
   c_sum  NUMBER := 0; 
   i NUMBER;
   BEGIN
      c_in_val := TO_CHAR( in_val );                
      i := LENGTH( c_in_val );
      WHILE i > 0 LOOP
         c_sum := c_sum + TO_NUMBER( SUBSTR( c_in_val, i, 1 ) );
         i := i - 1;
      END LOOP; 
   RETURN TO_NUMBER( c_in_val || MOD( c_sum, 10 ) );
END add_check_digit;
/
SHOW ERRORS

Then create the table:

CREATE TABLE a_table ( id_col number(10) );  

Here is a trigger to enforce the rule, since Oracle doesn't allow self-defined functions in check-constraints:

CREATE OR REPLACE TRIGGER ar_iu_a_table 
     AFTER INSERT 
        OR UPDATE OF id_col
     ON a_table 
     FOR EACH ROW 
BEGIN
  IF :new.id_col != add_check_digit( TRUNC( :new.id_col / 10 ) ) THEN
    RAISE_APPLICATION_ERROR( -20000, 'id_col failed check-digit-test !' );
  END IF;
END;
/
SHOW ERRORS

Finally, here is how to use the function for generating new datasets:

INSERT INTO a_table ( id_col) VALUES ( add_check_digit( your_id_sequence.nextval() ) )

For More Information

  • What do you think about this tip? E-mail the Editor at

    Requires Free Membership to View


This was first published in May 2002

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.