# 自增主键达到上限，无法插入数据
#### 场景现象
插入数据时报错：ERROR 1062 (23000): Duplicate entry 'xxx' for key 'xxx'
#### 原因分析
自增主键的字段取值达到上限，无法继续增长，导致新插入的数据生成的自增主键值与表中上一条数据相同，因为自增主键的值不可重复，插入失败报错。
```
mysql> create table auto_test5(id tinyint not null AUTO_INCREMENT, name varchar(8), PRIMARY KEY (`id`)); 
Query OK, 0 rows affected (0.06 sec) mysql> insert into auto_test5(name) values('A'),('B'),('C'); 
Query OK, 3 rows affected (0.00 sec) 
Records: 3  Duplicates: 0  Warnings: 0  
mysql> select * from auto_test5; 
+----+------+ 
| id | name | 
+----+------+ 
|  1 | A    | 
|  2 | B    | 
|  3 | C    | 
+----+------+ 
3 rows in set (0.00 sec)  
mysql> alter table auto_test5 AUTO_INCREMENT=125; 
Query OK, 0 rows affected (0.05 sec) 
Records: 0  Duplicates: 0  Warnings: 0  
mysql> show create table auto_test5; 
+------------+-------------------------------------------------------------+ 
| Table      | Create Table                                                | 
+------------+-------------------------------------------------------------+ 
| auto_test5 | CREATE TABLE `auto_test5` (   
`id` tinyint NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   
PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=125 DEFAULT CHARSET=utf8 | 
+------------+-------------------------------------------------------------+ 
mysql> insert into auto_test5(name) values('X'),('Y'),('Z'); 
Query OK, 3 rows affected (0.00 sec) 
Records: 3  Duplicates: 0  Warnings: 0  
mysql> select * from auto_test5; 
+-----+------+ 
| id  | name | 
+-----+------+ 
|   1 | A    | 
|   2 | B    | 
|   3 | C    | 
| 125 | X    | 
| 126 | Y    | 
| 127 | Z    | 
+-----+------+ 
6 rows in set (0.00 sec) 
mysql> show create table auto_test5; 
+------------+-------------------------------------------------------------+ 
| Table      | Create Table                                                | 
+------------+-------------------------------------------------------------+ 
| auto_test5 | CREATE TABLE `auto_test5` (   `id` tinyint NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=127 DEFAULT CHARSET=utf8 | 
+------------+-------------------------------------------------------------+ 
mysql> insert into auto_test5(name) values('D'); 
ERROR 1062 (23000): Duplicate entry '127' for key 'auto_test5.PRIMARY'
```
#### 解决方案
- 如果数据变化较多，表中实际数据量远小于自增主键的容量，则可以考虑将该表的数据全量导入新表，删除原表，然后rename将新表名改回原表名。（数据导入导出的方法有多种，此处仅为示例）
  ```
  mysql>  create table auto_test5_tmp(id tinyint not null AUTO_INCREMENT, name varchar(8), PRIMARY KEY (`id`)); 
  Query OK, 0 rows affected (0.07 sec) 
  mysql> insert into auto_test5_tmp select 0,name from auto_test5; 
  Query OK, 6 rows affected (0.01 sec) 
  Records: 6  Duplicates: 0  Warnings: 0 
  mysql> select * from auto_test5_tmp; 
  +----+------+ 
  | id | name | 
  +----+------+ 
  |  1 | A    | 
  |  2 | B    | 
  |  3 | C    | 
  |  4 | X    | 
  |  5 | Y    | 
  |  6 | Z    | 
  +----+------+ 
  mysql> drop table auto_test5; 
  mysql> rename table auto_test5_tmp to auto_test5; 
  Query OK, 0 rows affected (0.12 sec)  
  mysql> select * from auto_test5; 
  +----+------+ 
  | id | name | 
  +----+------+ 
  |  1 | A    | 
  |  2 | B    | 
  |  3 | C    | 
  |  4 | X    | 
  |  5 | Y    | 
  |  6 | Z    | 
  +----+------+ 
  6 rows in set (0.01 sec) 
  mysql> show create table auto_test5; 
  +------------+-----------------------------------------------------------+ 
  | Table      | Create Table                                              | 
  +------------+-----------------------------------------------------------+ 
  | auto_test5 | CREATE TABLE `auto_test5` (   
  `id` tinyint NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   
  PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8 | 
  +------------+-----------------------------------------------------------+
  ```
  
- 如果确实是自增主键的取值范围不够，则修改自增主键的字段类型，使其能存更多、更大的数据。
  ```
  mysql> select * from auto_test6; 
  +-----+------+ 
  | id  | name | 
  +-----+------+ 
  |   1 | A    | 
  |   2 | B    | 
  |   3 | C    | 
  | 125 | X    | 
  | 126 | Y    | 
  | 127 | Z    | 
  +-----+------+ 
  6 rows in set (0.00 sec)  
  mysql> show create table auto_test6; 
  +------------+-------------------------------------------------------------+ 
  | Table      | Create Table                                                | 
  +------------+-------------------------------------------------------------+ 
  | auto_test6 | CREATE TABLE `auto_test6` (   
  `id` tinyint NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   
  PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=127 DEFAULT CHARSET=utf8 | 
  +------------+-------------------------------------------------------------+ 
  mysql> alter table auto_test6  modify column id int NOT NULL AUTO_INCREMENT; 
  Query OK, 6 rows affected (0.15 sec) 
  Records: 6  Duplicates: 0  Warnings: 0  
  mysql> show create table auto_test6; 
  +------------+-------------------------------------------------------------+ 
  | Table      | Create Table                                                | 
  +------------+-------------------------------------------------------------+ 
  | auto_test6 | CREATE TABLE `auto_test6` (   
  `id` int NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   
  PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=128 DEFAULT CHARSET=utf8 | 
  +------------+-------------------------------------------------------------+ 
  1 row in set (0.00 sec)  
  mysql> insert into auto_test6(name) values('D'); 
  Query OK, 1 row affected (0.01 sec)  
  mysql> select * from auto_test6; 
  +-----+------+ 
  | id  | name | 
  +-----+------+ 
  |   1 | A    | 
  |   2 | B    | 
  |   3 | C    | 
  | 125 | X    | 
  | 126 | Y    | 
  | 127 | Z    | 
  | 128 | D    | 
  +-----+------+ 
  7 rows in set (0.00 sec)  
  mysql> show create table auto_test6; 
  +------------+-------------------------------------------------------------+ 
  | Table      | Create Table                                                | 
  +------------+-------------------------------------------------------------+ 
  | auto_test6 | CREATE TABLE `auto_test6` (   
  `id` int NOT NULL AUTO_INCREMENT,   `name` varchar(8) DEFAULT NULL,   
  PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=129 DEFAULT CHARSET=utf8 | 
  +------------+-------------------------------------------------------------+ 
  1 row in set (0.01 sec)
  ```