using a mysql trigger to copy and paste value within the same row, is it possible?

I have a form in which the user enters their e-mail address along with their use开发者_Python百科rname and desired password. How would I go about creating a trigger that will copy the e-mail address into the username field (located in the same row) if the user doesn't select a user name?

Table: Users

+-------+---------+------+-----+---------+
|   uName  |   uPassword   |   uEmail    |
+-------+---------+------+-----+---------+
|   NULL   |    pass123    | uzr@sql.com |
+-------+---------+------+-----+---------+

---

Are you sure you need a trigger to do that? If you have control over your insert or update statement (which you may not if you're using an ORM) you can do something like this:

mysql> insert into t4 (uemail, upassword, uname) SELECT  @email:='joe@joe.com', 'secretpassword', ifnull(null, @email);
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select * from t4 where uemail='joe@joe.com';
+-------------+----------------+-------------+
| uname       | upassword      | uemail      |
+-------------+----------------+-------------+
| joe@joe.com | secretpassword | joe@joe.com |
+-------------+----------------+-------------+
1 row in set (0.00 sec)

If you don't have control over the insert/update statements, then yes, you can use a trigger for that:

mysql> create trigger setuname before insert on t4
    -> for each row begin
    ->   set new.uname=ifnull(new.uname, new.uemail);
    -> end;
    -> |
Query OK, 0 rows affected (0.09 sec)

mysql> delimiter ;

mysql> insert into t4 (uname, uemail, upassword) values (null, 'joe@joe.com', 'secretpassword');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t4;
+-------------+----------------+-------------+
| uname       | upassword      | uemail      |
+-------------+----------------+-------------+
| joe@joe.com | secretpassword | joe@joe.com |
+-------------+----------------+-------------+
1 row in set (0.00 sec)