Question

Here is my table:

Id    Password       Status
1     a6cc890..       1

I have a trigger upon Password which is used to encrypt the field.

The trigger is as below:

-- Trigger DDL Statements
DELIMITER $$

USE `ediftpdb`$$

CREATE
DEFINER=`edidbo`@`%`
TRIGGER `ediftpdb`.`trigger_format_passwd`
BEFORE INSERT ON `ediftpdb`.`users`
FOR EACH ROW
SET NEW.passwd=md5(NEW.passwd)$$

CREATE
DEFINER=`edidbo`@`%`
TRIGGER `ediftpdb`.`trigger_format_passwd_update`
BEFORE UPDATE ON `ediftpdb`.`users`
FOR EACH ROW
SET NEW.passwd=md5(NEW.passwd)$$

To my surprise, the trigger is fired when I update Status, and the password is encrypted again!

What should I do to resolve this issue?

Answer 1

If you update Status, you’re doing an UPDATE and all of the UPDATE triggers will fire. All you need to do is compare the new and old values of passwd and only apply your MD5 if they are different. Lucky for you, MySQL supplies OLD and NEW row aliases:

You can refer to columns in the subject table (the table associated with the trigger) by using the aliases OLD and NEW. OLD.col_name refers to a column of an existing row before it is updated or deleted. NEW.col_name refers to the column of a new row to be inserted or an existing row after it is updated. Try using IF:

BEFORE UPDATE ON `ediftpdb`.`users`
FOR EACH ROW
SET NEW.passwd = IF(NEW.passwd = OLD.passwd, NEW.passwd, md5(NEW.passwd))

This shouldn’t change NEW.passwd unless NEW.passwd (the new password) and OLD.passwd (the hashed password that is already in the database) are different. Of course, this might fail if someone manages to enter the MD5 of their old password as their new password but that’s pretty unlikely.