ON UPDATE CASCADE, is it correct that b remains NULL? even after update?

[Morten Gulbrandsen]

--------------
SELECT Version()
--------------

+--------------------+
| Version() |
+--------------------+
| 5.0.0-alpha-max-nt |
+--------------------+
1 row in set (0.00 sec)

--------------
DROP TABLE IF EXISTS A
--------------

Query OK, 0 rows affected (0.04 sec)

--------------
CREATE TABLE A
(
a CHAR(9) NOT NULL,
b CHAR(9),
c INT NOT NULL DEFAULT 1,
PRIMARY KEY (a),
INDEX (b, c)
)ENGINE = INNODB
--------------

Query OK, 0 rows affected (0.07 sec)

--------------
SHOW WARNINGS
--------------

Empty set (0.00 sec)

--------------
DESCRIBE A
--------------

+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| a | char(9) | | PRI | | |
| b | char(9) | YES | MUL | NULL | |
| c | int(11) | | | 1 | |
+-------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)

--------------
ALTER TABLE A
ADD FOREIGN KEY (b) REFERENCES A(a)
ON DELETE SET NULL
ON UPDATE CASCADE
--------------

Query OK, 0 rows affected (0.18 sec)
Records: 0 Duplicates: 0 Warnings: 0

--------------
SHOW WARNINGS
--------------

Empty set (0.00 sec)

--------------
DESCRIBE A
--------------

+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| a | char(9) | | PRI | | |
| b | char(9) | YES | MUL | NULL | |
| c | int(11) | | | 1 | |
+-------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)

--------------
SELECT * FROM A
--------------

Empty set (0.00 sec)

--------------
INSERT INTO A (a) VALUES ('a0')
--------------

Query OK, 1 row affected (0.03 sec)

--------------
INSERT INTO A (a) VALUES ('a1')
--------------

Query OK, 1 row affected (0.02 sec)

--------------
SELECT * FROM A
--------------

+----+------+---+
| a | b | c |
+----+------+---+
| a0 | NULL | 1 |
| a1 | NULL | 1 |
+----+------+---+
2 rows in set (0.00 sec)

--------------
UPDATE A SET a='updated' WHERE a='a0'
--------------

Query OK, 1 row affected (0.03 sec)
Rows matched: 1 Changed: 1 Warnings: 0

--------------
SELECT * FROM A
--------------

+---------+------+---+
| a | b | c |
+---------+------+---+
| a1 | NULL | 1 |
| updated | NULL | 1 |
+---------+------+---+
2 rows in set (0.00 sec)

Bye