MySQl 序列的使用讲解

使用AUTO_INCREMENT

mysql> CREATE TABLE insect
    -> (
    -> id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    -> PRIMARY KEY (id),
    -> name VARCHAR(30) NOT NULL, # type of insect
    -> date DATE NOT NULL, # date collected
    -> origin VARCHAR(30) NOT NULL # where collected
);
Query OK, 0 rows affected (0.02 sec)
mysql> INSERT INTO insect (id,name,date,origin) VALUES
    -> (NULL,'housefly','2001-09-10','kitchen'),
    -> (NULL,'millipede','2001-09-10','driveway'),
    -> (NULL,'grasshopper','2001-09-10','front yard');
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> SELECT * FROM insect ORDER BY id;
+----+-------------+------------+------------+
| id | name        | date       | origin     |
+----+-------------+------------+------------+
|  1 | housefly    | 2001-09-10 | kitchen    |
|  2 | millipede   | 2001-09-10 | driveway   |
|  3 | grasshopper | 2001-09-10 | front yard |
+----+-------------+------------+------------+
3 rows in set (0.00 sec)

获取AUTO_INCREMENT值

在MySQL的客户端中可以使用SQL中的LAST_INSERT_ID()函数来获取最后的插入表中的自增列的值。

PERL 实例

$dbh->do ("INSERT INTO insect (name,date,origin)
VALUES('moth','2001-09-14','windowsill')");
my $seq = $dbh->{mysql_insertid};

PHP 实例(PHP通过mysql_insert_id()函数来获取执行的插入SQL语句中AUTO_INCREMENT列的值。)

mysql_query ("INSERT INTO insect (name,date,origin)
VALUES('moth','2001-09-14','windowsill')", $conn_id);
$seq = mysql_insert_id ($conn_id);

重置序列

如果你删除了数据表中的多条记录，并希望对剩下数据的AUTO_INCREMENT列进行重新排列，那么你可以通过删除自增的列，然后重新添加来实现。 不过该操作要非常小心，如果在删除的同时又有新记录添加，有可能会出现数据混乱。操作如下所示：

mysql> ALTER TABLE insect DROP id;
mysql> ALTER TABLE insect
    -> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST,
    -> ADD PRIMARY KEY (id);

设置序列的开始值

mysql> CREATE TABLE insect
    -> (
    -> id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    -> PRIMARY KEY (id),
    -> name VARCHAR(30) NOT NULL, 
    -> date DATE NOT NULL,
    -> origin VARCHAR(30) NOT NULL
)engine=innodb auto_increment=100 charset=utf8;

或者也可以在表创建成功后，通过以下语句来实现：

mysql> ALTER TABLE t AUTO_INCREMENT = 100;