如何在mysql中插入AUTO_INCREMENT行的键0？

Question

可能重复： How to force MySQL to take 0 as a valid auto-increment value

我知道我可以对现有行进行更新，但是否可以使用id 0插入一行？

mysql> create table inc( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, sz TEXT);
Query OK, 0 rows affected (0.10 sec)

mysql> insert into inc(id, sz) select 25, "a";
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into inc(id, sz) select 25, "a";
ERROR 1062 (23000): Duplicate entry '25' for key 'PRIMARY'
mysql> insert into inc(id, sz) select 27, "b";
Query OK, 1 row affected (0.04 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into inc(id, sz) select -5, "c";
Query OK, 1 row affected (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into inc(id, sz) select 0, "d";
Query OK, 1 row affected (0.15 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select * from inc;
+----+------+
| id | sz   |
+----+------+
| -5 | c    |
| 25 | a    |
| 27 | b    |
| 28 | d    |
+----+------+
4 rows in set (0.00 sec)

Answer 1

来自http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html

“没有为AUTO_INCREMENT列指定值，因此MySQL自动分配序列号。您还可以显式地将NULL或0赋值给该列以生成序列号。”

所以，使用0似乎只需要告诉auto_increment。

但是，如果要分配ID号，我不知道为什么要定义使用AUTO_INCREMENT的列？