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

Question

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.

Answer 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.

Answer 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/

Answer 3

Actually, we can can set regular expression within check constraints in MySQL. Eg.,:

create table fk 
  ( 
    empid int not null unique, 
    age int check(age between 18 and 60), 
    email varchar(20) default 'N/A', 
    secondary_email varchar(20) check(secondary_email RLIKE'^[a-zA-Z]@[a-zA-Z0-9]\.[a-z,A-Z]{2,4}'), 
    deptid int check(deptid in(10,20,30)) 
  ) 
; 

This INSERT query will work: insert into fk values(1,19,'a@a.com','a@b.com', 30);

This INSERT query will not work: insert into fk values(2,19,'a@a.com','a@bc.com', 30);