关于mysql的自增id测试，innodb和myisam下的不同表现

来源：互联网发布：unity3d vr 室内场景编辑：程序博客网时间：2024/05/21 09:55

innodb引擎下的自增id测试

1 innodb引擎下，如果显示insert了最大值，那么下次的AUTO_INCREMENT值就是这个最大值+1

mysql> select * from innodb_test;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+
3 rows in set (0.00 sec)

mysql> insert into innodb_test(id) values(100);
Query OK, 1 row affected (0.00 sec)

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=101 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

2 如果这时候再把其中一个id值update成105，那么下次的AUTO_INCREMENT却还是不变

mysql> update innodb_test set id=105 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> select * from innodb_test;
+-----+
| id |
+-----+
| 2 |
| 3 |
| 100 |
| 105 |
+-----+
4 rows in set (0.00 sec)

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=101 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

3 如果这时再利用自增段去插入，到了105的时候是会报错的

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into innodb_test values();
ERROR 1062 (23000): Duplicate entry '105' for key 'PRIMARY'

4 这时继续插入，不会报错，因为刚才即使报错了，AUTO_INCREMENT值依旧会增加

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.00 sec)

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=107 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> select * from innodb_test;
+-----+
| id |
+-----+
| 2 |
| 3 |
| 100 |
| 101 |
| 102 |
| 103 |
| 104 |
| 105 |
| 106 |
+-----+
9 rows in set (0.00 sec)

5 如果db重启了，那么innodb表在启动后，AUTO_INCREMENT值会自动检测出当前表中的最大值+1

测试5.1 手工修改AUTO_INCREMENT值为110，重启db，发现AUTO_INCREMENT还是原来的没有修改前的AUTO_INCREMENT，因为我只修改了但并没有插入数据，顺便提一句，AUTO_INCREMENT值只能设置得比当前值大，不能比当前值小，如果设置得比当前值小，它会默认调整到当前的最大值。

mysql> alter table innodb_test AUTO_INCREMENT=110;
Query OK, 9 rows affected (0.01 sec)
Records: 9 Duplicates: 0 Warnings: 0

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> alter table innodb_test AUTO_INCREMENT=10;
Query OK, 9 rows affected (0.00 sec)
Records: 9 Duplicates: 0 Warnings: 0

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=107 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> alter table innodb_test AUTO_INCREMENT=110;
Query OK, 9 rows affected (0.00 sec)
Records: 9 Duplicates: 0 Warnings: 0

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

这时重启db发现又变回了107，符合刚才的猜测
[root@10-10-175-111 ~]# service mysqld restart
Stopping mysqld: [ OK ]
Starting mysqld: [ OK ]
mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=107 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

测试5.2 插入一条111的记录，重启db，这时AUTO_INCREMENT应该不变，符合猜测

mysql> select * from innodb_test;
+-----+
| id |
+-----+
| 2 |
| 3 |
| 100 |
| 101 |
| 102 |
| 103 |
| 104 |
| 105 |
| 106 |
+-----+
9 rows in set (0.00 sec)

mysql> insert into innodb_test(id) values(111);
Query OK, 1 row affected (0.00 sec)

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=112 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> Ctrl-C -- exit!
Aborted
[root@10-10-175-111 ~]# service mysqld restart
Stopping mysqld: [ OK ]
Starting mysqld: [ OK ]
mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=112 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

测试5.3，删除该表的所有记录，不重启db的话AUTO_INCREMENT不变，如果重启db则AUTO_INCREMENT会置空，重新计数，符合猜测

mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=112 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> delete from innodb_test;
Query OK, 10 rows affected (0.01 sec)

mysql> Ctrl-C -- exit!
Aborted
[root@10-10-175-111 ~]# service mysqld restart
Stopping mysqld: [ OK ]
Starting mysqld: [ OK ]
mysql> show create table innodb_test\G
*************************** 1. row ***************************
Table: innodb_test
Create Table: CREATE TABLE `innodb_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.01 sec)

mysql> insert into innodb_test values();
Query OK, 1 row affected (0.01 sec)

mysql> select * from innodb_test;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.00 sec)

myisam引擎下自增id

1 myisam引擎下，如果显示insert了最大值，那么下次的AUTO_INCREMENT值就是这个最大值+1

mysql> insert into myisam_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into myisam_test values();
Query OK, 1 row affected (0.00 sec)

mysql> insert into myisam_test(id) values(5);
Query OK, 1 row affected (0.00 sec)

mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

2 如果这时候再把其中一个id值update成105，那么下次的AUTO_INCREMENT就会变成106(这和innodb是不同的！)

mysql> update myisam_test set id=105 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> select * from myisam_test;
+-----+
| id |
+-----+
| 2 |
| 5 |
| 105 |
+-----+
3 rows in set (0.00 sec)

mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=106 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

3 当db重启后，myisam引擎的AUTO_INCREMENT值不变

测试3.1 手工修改AUTO_INCREMENT值为110，重启db，发现AUTO_INCREMENT还是110，符合猜测

mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=106 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> alter table myisam_test AUTO_INCREMENT=110;
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0

mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
[root@10-10-175-111 ~]# service mysqld restart
Stopping mysqld: [ OK ]
Starting mysqld: [ OK ]
mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

测试3.2 删除该表下的所有记录，重启db，AUTO_INCREMENT值不变

mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> delete from myisam_test;
Query OK, 3 rows affected (0.00 sec)

Stopping mysqld: [ OK ]
Starting mysqld: [ OK ]
mysql> show create table myisam_test\G
*************************** 1. row ***************************
Table: myisam_test
Create Table: CREATE TABLE `myisam_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=110 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> select * from myisam_test;
Empty set (0.00 sec)

mysql> insert into myisam_test values();
Query OK, 1 row affected (0.00 sec)

mysql> select * from myisam_test;
+-----+
| id |
+-----+
| 110 |
+-----+
1 row in set (0.00 sec)

得到的启示

1 现在都提倡都使用innodb引擎，如果将myisam引擎转换过来的时候，一定要小心这两个引擎在自增id上的不同表现
2 自增id的列不要随意显示指定自增id值，myisam还好些，innodb是可能引起重复主键错误
3 有些主从使用不同引擎的要注意了，同样也是两种引擎不同表现会带来一些意想不到的问题

2 0