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 10
Server version: 5.5.52-MariaDB MariaDB Server

Copyright (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 changed
MariaDB [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autocommit
Query 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]>