MySQL Example of using CONCAT() and UPDATE
This code updates the column named 'phone_number' in the table called 'user' by concatenating '0' in front of the new phone_number.
The new phone_number is old phone_number minus the first 4 characters or beginning from the 5th character.
The update will only be applied to the records with id between 3 and 30 exclusive.
UPDATE user SET phone_number = CONCAT('0', SUBSTRING(phone_number, 5)) WHERE id > 3 AND id < 30;
See how the code is shorter than the explanation?
Biniam from Ethiopia.
This code is posted at http://dev.mysql.com/doc/refman/5.6/en/string-functions.html#c12657