MySQL - set dynamic default value

Question

I have table of users in my MySQL database. Is it possible to set default value of column profile_url to value of column Id ?

Answer 1

You could use trigger to implement the feature. For example:

CREATE TRIGGER defaultUrl
BEFORE INSERT ON MyTable
FOR EACH ROW 
SET NEW.profile_url = IFNULL(NEW.profile_url, NEW.id);

The expression creates a trigger named defaultUrl that activates before each row inserted into MyTable. If defaultUrl is NULL, the id value is used.