Updated on 2023-10-19 GMT+08:00
Auto-Increment Field Value Jump
If the values of the auto-increment field are discontinuous, the possible causes are as follows:
- The increment is not 1.
mysql> show variables like 'auto_inc%'; +--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 2 | | auto_increment_offset | 1 | +--------------------------+-------+ mysql> select * from auto_test1; +----+ | id | +----+ | 2 | | 4 | | 6 | | 8 | +----+
- The value of AUTO_INCREMENT is changed.
mysql> select * from animals; +----+-----------+ | id | name | +----+-----------+ | 1 | dog | | 2 | cat | | 3 | penguin | +----+-----------+ mysql> show create table animals; +---------+-----------------------------------------------------+ | Table | Create Table | +---------+-----------------------------------------------------+ | animals | CREATE TABLE `animals` ( `id` mediumint NOT NULL AUTO_INCREMENT, `name` char(30) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 | +---------+-----------------------------------------------------+ mysql> alter table animals AUTO_INCREMENT=100; Query OK, 0 rows affected (0.04 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table animals; +---------+-----------------------------------------------------+ | Table | Create Table | +---------+-----------------------------------------------------+ | animals | CREATE TABLE `animals` ( `id` mediumint NOT NULL AUTO_INCREMENT, `name` char(30) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=100 DEFAULT CHARSET=utf8 | +---------+-----------------------------------------------------+ mysql> INSERT INTO animals (id,name) VALUES(0,'rabbit'); Query OK, 1 row affected (0.00 sec) mysql> select * from animals; +-----+-----------+ | id | name | +-----+-----------+ | 1 | dog | | 2 | cat | | 3 | penguin | | 100 | rabbit | +-----+-----------+ 9 rows in set (0.00 sec)
- The value of the auto-increment field is specified when data is inserted.
mysql> select * from animals; +----+-----------+ | id | name | +----+-----------+ | 1 | dog | | 2 | cat | | 3 | penguin | +----+-----------+ mysql> INSERT INTO animals (id,name) VALUES(100,'rabbit'); Query OK, 1 row affected (0.00 sec) mysql> select * from animals; +-----+-----------+ | id | name | +-----+-----------+ | 1 | dog | | 2 | cat | | 3 | penguin | | 100 | rabbit | +-----+-----------+ 9 rows in set (0.00 sec)
- If a transaction is not committed or is rolled back, the value of AUTO_INCREMENT increases but does not decrease after the transaction is rolled back. When data is inserted again, the value of the auto-increment field jumps.
mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ 1 row in set (0.00 sec) mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | +----+ mysql> begin; Query OK, 0 rows affected (0.02 sec) mysql> insert into auto_test1 values (0),(0),(0); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | +----+ 6 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ 1 row in set (0.00 sec) mysql> rollback; Query OK, 0 rows affected (0.05 sec) mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | +----+ 3 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ mysql> insert into auto_test1 values (0),(0),(0); Query OK, 3 rows affected (0.01 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | | 7 | | 8 | | 9 | +----+ 6 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+-----------------------------------------+ | Table | Create Table | +------------+-----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8 | +------------+-----------------------------------------+
- After data is inserted, the value of AUTO_INCREMENT changes. But when the corresponding data row is deleted, the value of AUTO_INCREMENT does not decrease. When data is inserted again, the value of the auto-increment field jumps.
mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ 1 row in set (0.00 sec) mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | +----+ mysql> insert into auto_test1 values (0),(0),(0); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | +----+ 6 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ 1 row in set (0.00 sec) mysql> delete from auto_test1 where id>3; mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | +----+ 3 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+----------------------------------------+ | Table | Create Table | +------------+----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 | +------------+----------------------------------------+ mysql> insert into auto_test1 values (0),(0),(0); Query OK, 3 rows affected (0.01 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from auto_test1; +----+ | id | +----+ | 1 | | 2 | | 3 | | 7 | | 8 | | 9 | +----+ 6 rows in set (0.00 sec) mysql> show create table auto_test1; +------------+-----------------------------------------+ | Table | Create Table | +------------+-----------------------------------------+ | auto_test1 | CREATE TABLE `auto_test1` ( `id` int NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8 | +------------+-----------------------------------------+
- If data insertion fails due to some reasons (for example, unique key conflict), the value of AUTO_INCREMENT may jump.
mysql> create table auto_test7(`id` int NOT NULL AUTO_INCREMENT, cred_id int UNIQUE, PRIMARY KEY (`id`)); Query OK, 0 rows affected (0.64 sec) mysql> insert into auto_test7 values(null, 1); Query OK, 1 row affected (0.03 sec) mysql> show create table auto_test7; +------------+-------------------------------+ | Table | Create Table | +------------+-------------------------------+ | auto_test7 | CREATE TABLE `auto_test7` ( `id` int NOT NULL AUTO_INCREMENT, `cred_id` int DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `cred_id` (`cred_id`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 | +------------+--------------------------------------------------------------+ 1 row in set (0.00 sec) mysql> insert into auto_test7 values(null, 1); ERROR 1062 (23000): Duplicate entry '1' for key 'auto_test7.cred_id' mysql> show create table auto_test7; +------------+--------------------------------------------------------------+ | Table | Create Table | +------------+--------------------------------------------------------------+ | auto_test7 | CREATE TABLE `auto_test7` ( `id` int NOT NULL AUTO_INCREMENT, `cred_id` int DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `cred_id` (`cred_id`)) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 | +------------+---------------------------------------------------------------+
- When data is inserted in batches (such as insert...select and load file), the auto-increment key is requested in batches. Two to the power of n sequence numbers are requested in each batch. If the sequence numbers are not used up, the sequence numbers will not be returned. As a result, the value of AUTO_INCREMENT may jump.
mysql> create table auto_test5_tmp(id tinyint not null AUTO_INCREMENT, name varchar(8), PRIMARY KEY (`id`)); Query OK, 0 rows affected (0.08 sec) mysql> select * from auto_test5; +----+------+ | id | name | +----+------+ | 1 | A | | 2 | B | | 3 | C | | 4 | X | | 5 | Y | | 6 | Z | | 8 | A | | 9 | B | | 10 | C | | 11 | X | | 12 | Y | | 13 | Z | +----+------+ 12 rows in set (0.00 sec) mysql> insert into auto_test5_tmp select 0,name from auto_test5; Query OK, 12 rows affected (0.01 sec) Records: 12 Duplicates: 0 Warnings: 0 mysql> select * from auto_test5_tmp; +----+------+ | id | name | +----+------+ | 1 | A | | 2 | B | | 3 | C | | 4 | X | | 5 | Y | | 6 | Z | | 7 | A | | 8 | B | | 9 | C | | 10 | X | | 11 | Y | | 12 | Z | +----+------+ 12 rows in set (0.00 sec) mysql> show create table auto_test5_tmp; +----------------+-------------------------------------------------------+ | Table | Create Table | +----------------+-------------------------------------------------------+ | auto_test5_tmp | CREATE TABLE `auto_test5_tmp` ( `id` tinyint NOT NULL AUTO_INCREMENT, `name` varchar(8) DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8 | +----------------+-------------------------------------------------------+
Parent topic: Basic Issues
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