The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows:AUTO_INCREMENT属性可用于为新行生成唯一标识：

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
);

INSERT INTO animals (name) VALUES
    ('dog'),('cat'),('penguin'),
    ('lax'),('whale'),('ostrich');

SELECT * FROM animals;

Which returns:返回：

+----+---------+
| id | name    |
+----+---------+
|  1 | dog     |
|  2 | cat     |
|  3 | penguin |
|  4 | lax     |
|  5 | whale   |
|  6 | ostrich |
+----+---------+

No value was specified for the AUTO_INCREMENT column, so MySQL assigned sequence numbers automatically. 没有为AUTO_INCREMENT列指定任何值，因此MySQL会自动分配序列号。You can also explicitly assign 0 to the column to generate sequence numbers, unless the NO_AUTO_VALUE_ON_ZERO SQL mode is enabled. 除非启用了NO_AUTO_VALUE_ON_ZERO SQL模式，否则也可以将0显式分配给列以生成序列号。For example:例如

INSERT INTO animals (id,name) VALUES(0,'groundhog');

If the column is declared NOT NULL, it is also possible to assign NULL to the column to generate sequence numbers. For example:如果列被声明为NOT NULL，也可以将NULL分配给列以生成序列号。例如

INSERT INTO animals (id,name) VALUES(NULL,'squirrel');

When you insert any other value into an AUTO_INCREMENT column, the column is set to that value and the sequence is reset so that the next automatically generated value follows sequentially from the largest column value. For example:在AUTO_INCREMENT列中插入任何其他值时，该列将被设置为该值，并且序列将被重置，以便下一个自动生成的值从最大列值开始依次出现。例如

INSERT INTO animals (id,name) VALUES(100,'rabbit');
INSERT INTO animals (id,name) VALUES(NULL,'mouse');
SELECT * FROM animals;
+-----+-----------+
| id  | name      |
+-----+-----------+
|   1 | dog       |
|   2 | cat       |
|   3 | penguin   |
|   4 | lax       |
|   5 | whale     |
|   6 | ostrich   |
|   7 | groundhog |
|   8 | squirrel  |
| 100 | rabbit    |
| 101 | mouse     |
+-----+-----------+

Updating an existing AUTO_INCREMENT column value also resets the AUTO_INCREMENT sequence.更新现有的AUTO_INCREMENT列值也会重置AUTO_INCREMENT序列。

You can retrieve the most recent automatically generated AUTO_INCREMENT value with the LAST_INSERT_ID() SQL function or the mysql_insert_id() C API function. These functions are connection-specific, so their return values are not affected by another connection which is also performing inserts.您可以使用LAST_INSERT_ID()SQL函数或mysql_insert_id()C API函数检索最新自动生成的AUTO_INCREMENT值。这些函数是特定于连接的，因此它们的返回值不受同时执行插入的另一个连接的影响。

Use the smallest integer data type for the AUTO_INCREMENT column that is large enough to hold the maximum sequence value you require. 对AUTO_INCREMENT列使用最小的整数数据类型，该数据类型足够大，可以容纳所需的最大序列值。When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. 当列达到数据类型的上限时，下一次尝试生成序列号失败。Use the UNSIGNED attribute if possible to allow a greater range. For example, if you use TINYINT, the maximum permissible sequence number is 127. 如果可能，请使用UNSIGNED属性以允许更大的范围。例如，如果使用TINYINT，则允许的最大序列号为127。For TINYINT UNSIGNED, the maximum is 255. 对于TINYINT UNSIGNED，最大值为255。See Section 11.1.2, “Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types.有关所有整数类型的范围，请参阅第11.1.2节，“整数类型（精确值）-Integer、INT、SMALLINT、TINYINT、MEDIUMINT、BIGINT”。

To start with an AUTO_INCREMENT value other than 1, set that value with CREATE TABLE or ALTER TABLE, like this:要从AUTO_INCREMENT值而不是1开始，请使用CREATE TABLE或ALTER TABLE设置该值，如下所示：

mysql> ALTER TABLE tbl AUTO_INCREMENT = 100;