1. 说明
在对带有AUTO_INCREMENT列的表delete掉所有数据时:
(1)对于MyISAM表,在delete表中所有数据时没有任何风险,随意折腾;
(2)对于InnoDB表,在delete表中所有数据时,是可能有风险的,可能会引入一个大坑,具体看后面的实验。
环境描述:RHEL 6.4 x86_64 + MySQL 5.6.19
blog地址:http://blog.csdn.net/hw_libo/article/details/40149173
在维护有AUTO_INCREMENT列的表时,另外一个注意点,参考:
http://blog.csdn.net/hw_libo/article/details/40097125
2. MyISAM表
MySQL [bosco]> CREATE TABLE `t7` ( -> `id` int(10) unsigned NOT NULL AUTO_INCREMENT, -> `name` varchar(20) NOT NULL DEFAULT '', -> PRIMARY KEY (`id`) -> ) ENGINE=MyISAM; Query OK, 0 rows affected (0.05 sec) MySQL [bosco]> insert into t7(name) values('GZ'),('SH'),('BJ'),('SZ'),('HZ'); Query OK, 5 rows affected (0.03 sec) Records: 5 Duplicates: 0 Warnings: 0 MySQL [bosco]> select * from t7; +----+------+ | id | name | +----+------+ | 1 | GZ | | 2 | SH | | 3 | BJ | | 4 | SZ | | 5 | HZ | +----+------+ 5 rows in set (0.00 sec) MySQL [bosco]> delete from t7; Query OK, 5 rows affected (0.03 sec) MySQL [bosco]> show create table t7\G *************************** 1. row *************************** Table: t7 Create Table: CREATE TABLE `t7` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(20) NOT NULL DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) MySQL [bosco]> insert into t7(name) values('NJ'); Query OK, 1 row affected (0.07 sec) MySQL [bosco]> select * from t7; +----+------+ | id | name | +----+------+ | 6 | NJ | +----+------+ 1 row in set (0.00 sec) 如果在delete from t2后,重启了mysqld,AUTO_INCREMENT并不会被重置: MySQL [bosco]> show create table t7\G *************************** 1. row *************************** Table: t7 Create Table: CREATE TABLE `t7` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(20) NOT NULL DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 1 row in set (0.00 sec)
3. InnoDB表
MySQL [bosco]> show create table t2\G *************************** 1. row *************************** Table: t2 Create Table: CREATE TABLE `t2` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(20) NOT NULL DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 1 row in set (0.00 sec) MySQL [bosco]> insert into t2(name) values('GZ'),('SH'),('BJ'),('SZ'),('HZ'); Query OK, 5 rows affected (0.04 sec) Records: 5 Duplicates: 0 Warnings: 0 MySQL [bosco1]> select * from t2; +----+------+ | id | name | +----+------+ | 1 | GZ | | 2 | SH | | 3 | BJ | | 4 | SZ | | 5 | HZ | +----+------+ 5 rows in set (0.00 sec) MySQL [bosco]> delete from t2; ## 直接将t2表中的数据全部删除,使用的是delete而非truncate Query OK, 5 rows affected (0.04 sec) MySQL [bosco]> insert into t2(name) values('NJ'); ## 再次插入数据时,自增id会自动为下一编号 Query OK, 1 row affected (0.02 sec) MySQL [bosco]> select * from t2; +----+------+ | id | name | +----+------+ | 6 | NJ | +----+------+ 1 row in set (0.00 sec) 但是,如果在delete from t2后,重启了mysqld,那么情况完全不一样了,这个重启会重置id。 MySQL [bosco]> insert into t2(name) values('FJ'); ## 再次插入数据时,自增id会被重置编号 Query OK, 1 row affected (0.02 sec) MySQL [bosco]> select * from t2; +----+------+ | id | name | +----+------+ | 1 | FJ | ## 再次插入新值时,id编号会重新从头开始 +----+------+ 1 row in set (0.00 sec)
blog地址:http://blog.csdn.net/hw_libo/article/details/40149173
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时间: 2024-10-12 17:47:16