mysql autoincrementoffset

mysql autoincrementoffset"/>

mysql autoincrementoffset

root@localhost][(none)]> show variables like ‘auto_inc%‘;+--------------------------+-------+

| Variable_name | Value |

+--------------------------+-------+

| auto_increment_increment | 1 |

| auto_increment_offset | 1 |

+--------------------------+-------+

2 rows in set (0.00 sec)

auto_increment_increment：自增值

auto_increment_offset：漂移值,也就是步长

由于auto_increment_increment 属于全局可变的变量，故此可以通过修改自增值来达到测试目的

[root@localhost][(none)]> create table boss.autoinc1(col int not null auto_increment primary key);

Query OK,0 rows affected (1.03sec)[root@localhost][(none)]> set @@auto_increment_increment=10;

Query OK,0 rows affected (0.00sec)[root@localhost][(none)]> show variables like ‘auto_inc%‘;+--------------------------+-------+

| Variable_name | Value |

+--------------------------+-------+

| auto_increment_increment | 10 |

| auto_increment_offset | 1 |

+--------------------------+-------+

2 rows in set (0.00 sec)

从上面可以看到，自增从10开始，那么此时插入数据会是什么结果？

[root@localhost][(none)]> insert into boss.autoinc1 values(null),(null),(null),(null);

Query OK,4 rows affected (0.29sec)

Records:4 Duplicates: 0 Warnings: 0

[root@localhost][(none)]> select col fromboss.autoinc1;+-----+

| col |

+-----+

| 1 |

| 11 |

| 21 |

| 31 |

+-----+

4 rows in set (0.00 sec)

从结果集来看，auto_increment_increment的自增，为下一个跟上一个的间隔为10，也就是11->21->31->41以此类推

此时，我们设置offset这个的偏移值，那么数据则会

[root@localhost][(none)]> create table boss.autoinc2(col int not null auto_increment primary key);

Query OK,0 rows affected (1.31sec)[root@localhost][(none)]> insert into boss.autoinc2 values(null),(null),(null),(null);

Query OK,4 rows affected (0.14sec)

Records:4 Duplicates: 0 Warnings: 0

[root@localhost][(none)]> select col fromboss.autoinc2;+-----+

| col |

+-----+

| 5 |

| 15 |

| 25 |

| 35 |

+-----+

4 rows in set (0.00 sec)

可以看到，第一个是从基数1偏移到5个值(1,2,3,4,5),然后自动增值，每次进10这么处理

本质的逻辑为  auto_increment_offset + N × auto_increment_increment  N表示第几次，从0的技术开始计算

比如5+0*10,5+1*10，即

[root@localhost][mysql]> set @@auto_increment_offset=5;

Query OK,0 rows affected (0.00sec)[root@localhost][mysql]> create table boss.autoinc6(col int not null auto_increment primary key);

Query OK,0 rows affected (0.36sec)[root@localhost][mysql]> set @@auto_increment_increment=10;

Query OK,0 rows affected (0.00sec)[root@localhost][mysql]> show variables like ‘auto_inc%‘;+--------------------------+-------+

| Variable_name | Value |

+--------------------------+-------+

| auto_increment_increment | 10 |

| auto_increment_offset | 5 |

+--------------------------+-------+

2 rows in set (0.00sec)[root@localhost][mysql]> insert into boss.autoinc6 values(null),(null),(null),(null);

Query OK,4 rows affected (0.08sec)

Records:4 Duplicates: 0 Warnings: 0

[root@localhost][mysql]> select col fromboss.autoinc6;+-----+

| col |

+-----+

| 5 |

| 15 |

| 25 |

| 35 |

+-----+

4 rows in set (0.00 sec)

MySQL 中有关auto_increment及auto_increment_offset方面的介绍

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