10

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.

nad2000
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Shamim Hafiz - MSFT
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    Short answer: Yes you can. Could you add more context ? Would you like to filter it at input ? If so why don't you filter when the user signs-up for example ? – HamZa Apr 14 '13 at 23:25
  • @HamZaDzCyberDeV No, not at input. I want to enforce this in the database. I understand it can be done by in the application layer, I was wondering if the same was possible in the database layer when creating the tables. – Shamim Hafiz - MSFT Apr 14 '13 at 23:37
  • When creating a table, you have to specify a column type, there is no "phone number" type. You may want to look at [triggers](http://dev.mysql.com/doc/refman/5.6/en/triggers.html) – HamZa Apr 14 '13 at 23:44

3 Answers3

18

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.

nad2000
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    Thanks. This is something I was looking for. I understand that all validation should be done at all layers, but I needed to know how it's done for data layer. – Shamim Hafiz - MSFT Apr 15 '13 at 04:06
  • This is the create table query: 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)) ) ; \n This INSERT query will work:\n insert into fk values(1,19,'a@a.com','a@b.com', 30);\n This INSERT query will not work:\n insert into fk values(2,19,'a@a.com','a@bc.com', 30); – Shubhankar Raj Jun 27 '21 at 02:36
  • So we can set regular expression in the Check Constraint of create table. – Shubhankar Raj Jun 27 '21 at 02:39
4

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/

Abit Gray
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1

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);

Shubhankar Raj
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