09.MySQL子查询和连接

0准备工作：

先为剑表添加两个属性：属性(attr)和类型(type)

mysql> ALTER TABLE sword ADD attr VARCHAR(4) NOT NULL;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE sword ADD type VARCHAR(8) NOT NULL;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0
m