mysql> CREATE TABLE tb5( -> id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY, -> username VARCHAR(20) NOT NULL UNIQUE KEY, -> age TINYINT UNSIGNED NOT NULL -> );这是建表的代码mysql> INSERT tb5(username,age) VALUE('Tom',22);Query OK, 1 row affected (0.00 sec)mysql> INSERT tb5(username,age) VALUE('Tom',21);ERROR 1062 (23000): Duplicate entry 'Tom' for key 'username'mysql> INSERT tb5(username,age) VALUE('tt',22);Query OK, 1 row affected (0.00 sec)这是插入数据的过程,出现了一个错误,然后就变成下面这样了mysql> SELECT * FROM tb5;+----+----------+-----+| id | username | age |+----+----------+-----+| 1 | Tom | 22 || 3 | tt | 22 |+----+----------+-----+我有点困惑,和unique key有关吗?
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