我对这个sql语句的含义感到困惑：
- SELECT exhibitor_categories+0 from exhibitor_registry
什么是Exhibitor_categories 0？它返回返回的每一行的数字.
Exhibitor_categories定义为：
- set('contemporary','classical impression / transitional','outdoor','home accessories')
谢谢你的时间 ：)
解决方法
它隐含地将设定值转换为INTEGER.
集合被视为位图,因此第一个值设置位0,第二个值设置位1等.
- MysqL> CREATE TABLE exhibitor_registry(exhibitor_categories set('contemporary','home accessories') NOT NULL);
- Query OK,0 rows affected (0.08 sec)
- MysqL> INSERT
- -> INTO exhibitor_registry
- -> VALUES ('contemporary,classical impression / transitional,outdoor');
- Query OK,1 row affected (0.03 sec)
- MysqL> SELECT exhibitor_categories
- -> FROM exhibitor_registry;
- +----------------------------------------------------------+
- | exhibitor_categories |
- +----------------------------------------------------------+
- | contemporary,outdoor |
- +----------------------------------------------------------+
- 1 row in set (0.00 sec)
- MysqL> SELECT exhibitor_categories + 0
- -> FROM exhibitor_registry;
- +--------------------------+
- | exhibitor_categories + 0 |
- +--------------------------+
- | 7 |
- +--------------------------+
- 1 row in set (0.00 sec)
