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?它返回每行的数字。
exhibitor_categories 的定义如下:
set('contemporary', 'classical impression / transitional', 'outdoor', 'home accessories')
感谢您的时间 :)
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?它返回每行的数字。
exhibitor_categories 的定义如下:
set('contemporary', 'classical impression / transitional', 'outdoor', 'home accessories')
INTEGER
。0
,第二个值设置位 1
,以此类推。mysql> CREATE TABLE exhibitor_registry(exhibitor_categories set('contemporary',
'classical impression / transitional', 'outdoor', '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,classical impression / transitional,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)
@Obay
: 一幅位图将2的幂次方相加,以防混淆。它是 2^0
+ 2^1 + 2^2 = 1 + 2 + 4 = 7
。如果是 6
,你就无法区分 1 + 2 + 3
和 2 + 4
。 - Quassnoiset
(位图),而不是一个enum
。存储outdoor
将把数值设置为4
。 - Quassnoi