MySQL數據庫auto_increment自增值回溯

本篇內容介紹了“數據庫auto_increment自增值回溯”的有關(guān)知識，在實(shí)際案例的操作過(guò)程中，不少人都會(huì )遇到這樣的困境，接下來(lái)就讓小編帶領(lǐng)大家學(xué)習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學(xué)有所成！

# 創(chuàng )建關(guān)于表t，其中a字段為主鍵自增

mysql> create table t(a bigint primary key auto_increment, b tinyint);

Query OK, 0 rows affected (0.03 sec)

# 插入一些數據

mysql> insert into t select null, 10;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into t select null, 20;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into t select null, 30;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into t select null, 40;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

# 查看表記錄

mysql> select * from t;

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

| a | b    |

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

| 1 |   10 |

| 2 |   20 |

| 3 |   30 |

| 4 |   40 |

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

4 rows in set (0.00 sec)

# 刪除最后一條數據

mysql> delete from t where a=4;

Query OK, 1 row affected (0.02 sec)

# 查看表創(chuàng )建語(yǔ)句，發(fā)現AUTO_INCREMENT=5

mysql> show create table t\G

*************************** 1. row ***************************

       Table: t

Create Table: CREATE TABLE `t` (

  `a` bigint(20) NOT NULL AUTO_INCREMENT,

  `b` tinyint(4) DEFAULT NULL,

  PRIMARY KEY (`a`)

) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

# 進(jìn)行主鍵回溯模擬

# 重啟數據庫

[root@mysql ~]# service mysqld restart

Shutting down MySQL.. SUCCESS!

Starting MySQL. SUCCESS!

# 重新查看表創(chuàng )建語(yǔ)句，發(fā)現AUTO_INCREMENT=4

mysql> show create table t\G

*************************** 1. row ***************************

       Table: t

Create Table: CREATE TABLE `t` (

  `a` bigint(20) NOT NULL AUTO_INCREMENT,

  `b` tinyint(4) DEFAULT NULL,

  PRIMARY KEY (`a`)

) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

# 繼續插入語(yǔ)句

mysql> insert into t select null, 50;

Query OK, 1 row affected (0.00 sec)

Records: 1  Duplicates: 0  Warnings: 0

# 查看表的數據，發(fā)現上述自增ID=4又重新出現

mysql> select * from t;

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

| a | b    |

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

| 1 |   10 |

| 2 |   20 |

| 3 |   30 |

| 4 |   50 |

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

4 rows in set (0.00 sec)

這是因為在MySQL5.7中的表的AUTO_INCREMENT是基于內存，不會(huì )持久化在磁盤(pán)中，每次啟動(dòng)數據庫時(shí)，會(huì )對每張表進(jìn)行max(auto_increment) + 1重新作為該表下一次的主鍵ID的自增值。在MySQL8.0中就不會(huì )出現該問(wèn)題，因為數據會(huì )在磁盤(pán)中持久化。