MySQL 數據類型之集合類型

• Set集合類型是字符類型，可以含有0個或多個值，其中的每個值都需要是在創建字段時指定的集合中
• 比如一個字段被指定為SET(‘one’, ‘two’) not null可以含有以下四種值
　　• ''
　　• 'one'
　　• 'two'
　　• 'one,two‘
• Set集合最大可以有255個值
• MySQL在存儲set集合時，同樣也是存儲為數字類型

mysql>  CREATE TABLE myset (col SET('a', 'b', 'c', 'd'));
Query OK, 0 rows affected (0.12 sec)

mysql> insert into myset values('a');
Query OK, 1 row affected (0.10 sec)

mysql> insert into myset values('a,b');
Query OK, 1 row affected (0.03 sec)

mysql> insert into myset values('a,d');
Query OK, 1 row affected (0.01 sec)

mysql> insert into myset values('a,bd');
ERROR 1265 (01000): Data truncated for column 'col' at row 1
mysql> insert into myset values('a,b,d');
Query OK, 1 row affected (0.05 sec)

mysql> insert into myset values('a,e');
ERROR 1265 (01000): Data truncated for column 'col' at row 1
mysql> select * from myset;
+-------+
| col   |
+-------+
| a     |
| a,b   |
| a,d   |
| a,b,d |
+-------+
4 rows in set (0.00 sec)

mysql> insert into myset values('d,a');
Query OK, 1 row affected (0.08 sec)

mysql> select * from myset;
+-------+
| col   |
+-------+
| a     |
| a,b   |
| a,d   |
| a,b,d |
| a,d   |
+-------+
5 rows in set (0.00 sec)