[MySQL] on duplicate key update 構文の UPDATE 句で VALUES 関数を使うと INSERT 句でセットしようとした値が取れる。

gistfile1.sql

4.1.21-community-nt 71> USE test;
Query OK, 0 rows affected (0.00 sec)

4.1.21-community-nt 72> CREATE TABLE `test` (
    ->   `id` bigint(20) unsigned NOT NULL auto_increment,
    ->   `age` int(10) unsigned NOT NULL default '0',
    ->   PRIMARY KEY  (`id`)
    -> ) ENGINE=InnoDB DEFAULT CHARSET=utf8
    -> ;
Query OK, 0 rows affected (0.16 sec)

4.1.21-community-nt 73> INSERT INTO test VALUES(1, 10);
Query OK, 1 row affected (0.04 sec)

4.1.21-community-nt 74> SELECT * FROM test;
+----+-----+
| id | age |
+----+-----+
|  1 |  10 |
+----+-----+
1 row in set (0.00 sec)

4.1.21-community-nt 75> INSERT INTO test VALUES(1, 20) ON DUPLICATE KEY UPDATE age = VALUES(age);
Query OK, 2 rows affected (0.04 sec)

4.1.21-community-nt 76> SELECT * FROM test;
+----+-----+
| id | age |
+----+-----+
|  1 |  20 |
+----+-----+
1 row in set (0.00 sec)

4.1.21-community-nt 77> INSERT INTO test SET id = 1,  age = 30 ON DUPLICATE KEY UPDATE age = VALUES(age);
Query OK, 2 rows affected (0.04 sec)

4.1.21-community-nt 78> SELECT * FROM test;
+----+-----+
| id | age |
+----+-----+
|  1 |  30 |
+----+-----+
1 row in set (0.00 sec)

4.1.21-community-nt 79> INSERT INTO test VALUES(1, 40) ON DUPLICATE KEY UPDATE age = VALUES(age) * 2;
Query OK, 2 rows affected (0.04 sec)

4.1.21-community-nt 80> SELECT * FROM test;
+----+-----+
| id | age |
+----+-----+
|  1 |  80 |
+----+-----+
1 row in set (0.00 sec)

http://dev.mysql.com/doc/refman/5.1/ja/miscellaneous-functions.html
VALUES(col_name)