简单来说，transaction就是用来恢复为以前的数据。

举个例子，我想把今天输入到数据库里的数据在晚上的时候全部删除，那么我们就可以在今天早上的时候开始transaction事物，令autocommit关闭并且执行commit，然后再开始输入数据，到晚上的时候，可以执行rollback恢复到今天没输入数据的状态，也就是恢复到commit前的数据。

[root@localhost ~]# mysql -uroot -p              #登录数据库Enter password: Welcome to the MariaDB monitor.  Commands end with ; or \g.Your MariaDB connection id is 10Server version: 5.5.52-MariaDB MariaDB ServerCopyright (c) 2000, 2016, Oracle, MariaDB Corporation Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.MariaDB [(none)]> show databases;+--------------------+| Database           |+--------------------+| information_schema || mysql              || performance_schema || test               |+--------------------+4 rows in set (0.00 sec)MariaDB [(none)]> create database bp                #我自己创建一个数据库用来做这个实验    -> ;Query OK, 1 row affected (0.00 sec)MariaDB [(none)]> MariaDB [(none)]> use bp;Database changedMariaDB [bp]> create table test(id int,name varchar(20));               #建表Query OK, 0 rows affected (0.08 sec)MariaDB [bp]> insert into test values(1,'123');                         Query OK, 1 row affected (0.06 sec)MariaDB [bp]> insert into test values(2,'323');Query OK, 1 row affected (0.01 sec)MariaDB [bp]> select * from test;+------+------+| id   | name |+------+------+|    1 | 123  ||    2 | 323  |+------+------+2 rows in set (0.00 sec)MariaDB [bp]> show variables like '%commit%';                       #查看autocommit是否关闭，可以看到现在开启着+-------------------------------------------+-------+| Variable_name                             | Value |+-------------------------------------------+-------+| aria_group_commit                         | none  || aria_group_commit_interval                | 0     || autocommit                                | ON    || innodb_commit_concurrency                 | 0     || innodb_flush_log_at_trx_commit            | 1     || innodb_use_global_flush_log_at_trx_commit | ON    |+-------------------------------------------+-------+6 rows in set (0.00 sec)MariaDB [bp]> set autocommit=0;                             #关闭autocommitQuery OK, 0 rows affected (0.00 sec)MariaDB [bp]> show variables like '%commit%';+-------------------------------------------+-------+| Variable_name                             | Value |+-------------------------------------------+-------+| aria_group_commit                         | none  || aria_group_commit_interval                | 0     || autocommit                                | OFF   || innodb_commit_concurrency                 | 0     || innodb_flush_log_at_trx_commit            | 1     || innodb_use_global_flush_log_at_trx_commit | ON    |+-------------------------------------------+-------+6 rows in set (0.00 sec)MariaDB [bp]> start transaction;                            #开始事物Query OK, 0 rows affected (0.00 sec)MariaDB [bp]> delete from test where id=1;Query OK, 1 row affected (0.00 sec)MariaDB [bp]> select * from test;+------+------+| id   | name |+------+------+|    2 | 323  |+------+------+1 row in set (0.00 sec)MariaDB [bp]> commit;                                   #记录前面的数据Query OK, 0 rows affected (0.01 sec)MariaDB [bp]> delete from test where id=2;              #删除数据Query OK, 1 row affected (0.00 sec)MariaDB [bp]> select * from test;Empty set (0.00 sec)MariaDB [bp]> rollback;                                 #回滚到commit记录的数据Query OK, 0 rows affected (0.00 sec)MariaDB [bp]> select * from test;                       #回滚成功+------+------+| id   | name |+------+------+|    2 | 323  |+------+------+1 row in set (0.00 sec)MariaDB [bp]>