Is it Possible to Enforce Data Checking in MySQL using Regular expression

Suppose I have an attribute called phone number and I would like to enforce certain validity on the entries to this field. Can I use regular expression for this purpose, since Regular Expression is very flexible at defining constraints.

Solution 1:

Yes, you can. MySQL supports regex (http://dev.mysql.com/doc/refman/5.6/en/regexp.html) and for data validation you should use a trigger since MySQL doesn't support CHECK constraint (you can always move to PostgreSQL as an alternative:). NB! Be aware that even though MySQL does have CHECK constraint construct, unfortunately MySQL (so far 5.6) does not validate data against check constraints. According to http://dev.mysql.com/doc/refman/5.6/en/create-table.html: "The CHECK clause is parsed but ignored by all storage engines."

You can add a check constraint for a column phone:

CREATE TABLE data (
  phone varchar(100)
);

DELIMITER $$
CREATE TRIGGER trig_phone_check BEFORE INSERT ON data
FOR EACH ROW 
BEGIN 
IF (NEW.phone REGEXP '^(\\+?[0-9]{1,4}-)?[0-9]{3,10}$' ) = 0 THEN 
  SIGNAL SQLSTATE '12345'
     SET MESSAGE_TEXT = 'Wroooong!!!';
END IF; 
END$$
DELIMITER ;


INSERT INTO data VALUES ('+64-221221442'); -- should be OK
INSERT INTO data VALUES ('+64-22122 WRONG 1442'); -- will fail with the error: #1644 - Wroooong!!! 

However you should not rely merely on MySQL (data layer in your case) for data validation. The data should be validated on all levels of your app.

Solution 2:

MySQL 8.0.16 (2019-04-25) and MariaDB 10.2.1 (2016-04-18) now not only parse CHECK constraint but also enforces it.

MySQL: https://dev.mysql.com/doc/refman/8.0/en/create-table-check-constraints.html

MariaDB: https://mariadb.com/kb/en/constraint/