MySQL stores SET and ENUM as numbers : Set « Data Types « MySQL Tutorial

1. MySQL Tutorial
2. Data Types
3. Set

They can be manipulated using numeric operations.

mysql>
mysql> CREATE Table Test(
    ->     Advertiser SET('A','B','C')
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql>
mysql> INSERT INTO Test (Advertiser) values('A, B');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql>
mysql>
mysql> SELECT * FROM Test WHERE Advertiser = 1;
+------------+
| Advertiser |
+------------+
| A          |
+------------+
1 row in set (0.02 sec)

mysql>
mysql> SELECT Advertiser, Advertiser + 0 FROM Test;
+------------+----------------+
| Advertiser | Advertiser + 0 |
+------------+----------------+
| A          |              1 |
+------------+----------------+
1 row in set (0.00 sec)

mysql>
mysql> drop table Test;
Query OK, 0 rows affected (0.00 sec)

mysql>