MySQL的索引与事务、存储引擎MyISA和InnoDB

MySQL索引与事务，视图，存储引擎MylSAM和lnnoDB

索引的概念

数据库中的索引与书籍中的目录类似：

1.一本书中，无须阅读整本书,利用目录就可以快速查找所需信息
2.书中的目录是一个词语列表，其中注明了包含各个词的页码

数据库索引：

1.在数据库中，索引使数据库程序无须对整个表进行扫描，就可以在其中找到所需数据
2.数据库中的索弓|是某个表中一列或者若干列值的集合，以及物理标识这些值的数据页的逻辑指针清单

索引的作用：

1.设置了合适的索引之后，数据库利用各种快速的定位技术，能够大大加快查询速率
2.特别是当表很大时，或者查询涉及到多个表时，使用索引可使查询加快成干倍
3.可以降低数据库的IO成本，并且索引还可以降低数据库的排序成本
4.通过创建唯一性索引保证数据表数据的唯一性
5.可以加快表与表之间的连接
6.在使用分组和排序时，可大大减少分组和排序时间

索引的分类

普通索引：

是最基本的索引类型，而且它没有唯一性之类的限制

唯一性索引：

这种索引和前面的"普通索引"基本相同，但有一个区别:索引列的所有值都只能出现一次，即必须唯一

主键：

主键是一种唯一性索引，但它必须指定为"PRIMARY KEY"

全文索引：

MySQL从3.23.23版开始支持全文索引和全文检索。在MySQL中全文索引的索引类型为FULLTEXT,全文索引可以在VARCHAR或者TEXT类型的列上创建

单列索引与多列索引：

索引可以是单列上创建的索引，也可以是在多列上创建的索引

创建索引的原则依据

1.表的主键、外键必须有索引
2.数据量超过300行的表应该有索引
3.经常与其他表进行连接的表，在连接字段.上应该建立索引
4.唯一性太差的字段不适合建立索引
5.更新太频繁地字段不适合创建索引6.经常出现在Where子句中的字段，特别是大表的字段,应该建立索引
7.索引应该建在选择性高的字段上
8.索引应该建在小字段上，对于大的文本字段甚至超长字段，不要建索引

事务的概念

1.事务是一种机制、一个操作序列，包含了一组数据库操作命令，并且把所有的命令作为-一个整体一起向系统提交或撤销操作请求，即这一组数据库命令要么都执行,要么都不执行
2.事务是一个不可分割的工作逻辑单元，在数据库系统上执行并发操作时，事务是最小的控制单元
3.适用于多用户同时操作的数据库系统的场景，如银行、保险公司及证券交易系统等等
4.通过事务的整体性以保证数据的一致性

事务的ACID特点

原子性(Atomicity)：

1.事务是一个完整的操作，事务的各元素是不可分的(原子的)
2.事务中的所有元素必须作为一个整体提交或回滚
3.如果事务中的任何元素失败，则整个事务将失败

一致性(Consistency)：

当事务完成时，数据必须处于一 致状态:在事务开始之前，数据库中存储的数据处于一致状态;在正在进行的事务中，数据可能处于不一致的状态;当事务成功完成时，数据必须再次回到已知的一致状态

隔离性(Isolation)：

1.对数据进行修改的所有并发事务是彼此隔离的，这表明事务必须是独立的，它不应以任何方式依赖于或影响其他事务
2.修改数据的事务可以在另一个使用相同数据的事务开始之前访问这些数据，或者在另一个使用相同数据的事务结束之后访问这些数据

持久性(Durability)：

1.事务持久性指不管系统是否发生故障，事务处理的结果都是永久的
2.一旦事务被提交，事务的效果会被永久地保留在数据库中

事务的操作

1.默认情况下MySQL的事务是自动提交的，当sql语句提交时事务便自动提交

2.手动对事务进行控制的方法：

①事务处理命令控制
②使用set设置事务处理方式

3.事务处理命令控制事务：

①begin：开始一个事务
②commit：提交一个事务
②rollback：回滚一个事务

4.使用set命令进行控制：

①set autocommit=0：禁止自动提交
②set autocommit=1：开启自动提交

存储引擎概念介绍

1.MySQL中的数据用各种不同的技术存储在文件中,每一种技术都使用不同的存储机制、索引技巧、锁定水平并最终提供不同的功能和能力，这些不同的技术以及配套的功能在MySQL中称为存储引擎

2.存储引擎就是MySQL将数据存储在文件系统中的存储方式或者存储格式
3.目前MySQL常用的两种存储引擎：

①MyISAM（适合读）
②InnoDB（适合写）

4.MySQL存储引擎是MySQL数据库服务器中的组件，负责为数据库执行实际的数据I/O操作

5.使用特殊存储引擎的主要优点之一在于， 仅需提供特殊应用所需的特性，数据库中的系统开销较小，具有更有效和更高的数据库性能

6.MySQL系统中，存储引擎处于文件系统之.上，在数据保存到数据文件之前会传输到存储引擎，之后按照各个存储引擎的存储格式进行存储

MyISAM的介绍

1.MyISAM存储引擎是MySQ关系数据库系统5.5版本之前默认的存储引擎，前身是ISAM

2.ISAM是一个定义明确且历经时间考验的数据表格管理方法，在设计之时就考虑到数据库被查询的次数要远大于更新的次数
3.SAM的特点：

①ISAM执行读取操作的速度很快,
②它不支持事务处理
③而且不占用大量的内存和存储资源
④不能够容错

MyISAM适用的生产场景举例：

1.公司业务不需要事务的支持
2.一般单方面读取数据比较多的业务，或单方面写入数据比较多的业务
3.MyISAM存储引擎数据读写都比较频繁场景不适合
4.使用读写并发访问相对较低的业务
5.数据修改相对较少的业务
6.对数据业务一致性要求不是非常高的业务
7.服务器硬件资源相对比较差

InnoDB特点介绍

1.支持事务:支持4个事务隔离级别
2.行级锁定，但是全表扫描仍然会是表级锁定
3.读写阻塞与事务隔离级别相关
4.具有非常高效的缓存特性:能缓存索引，也能缓存数据
5.表与主键以簇的方式存储
6.支持分区、表空间，类似oracle数据库
7.支持外键约束，5.5以前不支持全文索引，5.5版本以后支持全文索引
8.对硬件资源要求还是比较高的场合

InnoDB适用生产场景分析

1.业务需要事务的支持
2.行级锁定对高并发有很好的适应能力，但需确保查询是通过索引来完成
3.业务数据更新较为频繁的场景， 如:论坛，微博等
4.业务数据一致性要求较高，例如:银行业务
5.硬件设备内存较大， 利用Innodb较好的缓存能力来提高内存利用率，减少磁盘IO的压力

配置存储引擎

1.在企业中选择好合适的存储引擎之后，就可以进行修改了
2.修改步骤：

①查看数据库可配置的存储引擎
②查看表正在使用的存储引擎
③配置存储引擎为所选择的类型

3.使用show engines查看系统支持的存储引擎查看表使用的存储引擎

方法1: show table status from库名where name='表名;
方法2: show create table表名

索引实操

1，进入数据库，创建数据库，创建表

[root@master2 ~]# mysql -uroot -p     ##进入数据库Enter password:     ##输入密码Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> create database school;    ##创建数据库schoolQuery OK, 1 row affected (0.00 sec)mysql> use school;       ##使用数据库Database changedmysql> create table info(        ##创建表        -> id int(4) not null primary key auto_increment,   ##设置主键，自动增加        -> name varchar(10) not null,       ##名字类型varchar不为空        -> address varchar(50) default 'nanjing',    ##默认南京        -> age int(3) not null);Query OK, 0 rows affected (0.02 sec)

2，向表中插入数据

mysql> insert into info (name,address,age) values ('zhangsan','beijing',20),('lisi','shanghai',22); ##插入数据Query OK, 2 rows affected (0.01 sec)Records: 2  Duplicates: 0  Warnings: 0mysql> select * from info;   ##查看表内容+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 |+----+----------+----------+-----+2 rows in set (0.00 sec)mysql> desc info;               ##查看表结构+---------+-------------+------+-----+---------+----------------+| Field   | Type        | Null | Key | Default | Extra          |+---------+-------------+------+-----+---------+----------------+| id      | int(4)      | NO   | PRI | NULL    | auto_increment || name    | varchar(10) | NO   |     | NULL    |                || address | varchar(50) | YES  |     | nanjing |                || age     | int(3)      | NO   |     | NULL    |                |+---------+-------------+------+-----+---------+----------------+4 rows in set (0.00 sec)

3，使用create，alter，创建表直接定义三种方式创建索引（普通索引，唯一性索引）

mysql> create index index_age on info (age);   ##创建普通索引Query OK, 0 rows affected (0.02 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from info;   ##查看表中的索引+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY   |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          1 | index_age |            1 | age         | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+2 rows in set (0.00 sec)mysql> drop index index_age on info;   ##删除表中的索引Query OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from info;        ##查看表中的索引         +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY  |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+1 row in set (0.01 sec)mysql> create unique index unique_name on info (name); ##创建唯一性索引Query OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from info;  ##查看表中索引+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY     |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          0 | unique_name |            1 | name        | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+2 rows in set (0.00 sec)mysql> drop index unique_name on info;  ##删除表中的索引Query OK, 0 rows affected (0.00 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from info;          ##查看表中的索引+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY  |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+1 row in set (0.00 sec)mysql> alter table info add unique index index_name (name);   ##使用alter插入表索引Query OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from info;   ##查看表中的索引+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY    |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          0 | index_name |            1 | name        | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+2 rows in set (0.00 sec)

4，创建两个表，进行关联，多表查询

mysql> create table user(     ##创建user表        -> id int(4) not null primary key auto_increment,   ##设置主键和自动增加        -> name varchar(10) not null,        -> score decimal not null,        -> hobby int(2) not null default '1',  ##默认1        -> index index_score (score));    ##设置索引scoreQuery OK, 0 rows affected (0.01 sec)mysql> desc user;  ##查看表结构+-------+---------------+------+-----+---------+----------------+| Field | Type          | Null | Key | Default | Extra          |+-------+---------------+------+-----+---------+----------------+| id    | int(4)        | NO   | PRI | NULL    | auto_increment || name  | varchar(10)   | NO   |     | NULL    |                || score | decimal(10,0) | NO   | MUL | NULL    |                || hobby | int(2)        | NO   |     | 1       |                |+-------+---------------+------+-----+---------+----------------+4 rows in set (0.00 sec)mysql> insert into user (name,score,hobby) values ('test01',88,1),('stu01',99,2),('wangwu',77,3); ##向表中插入数据Query OK, 3 rows affected (0.00 sec)Records: 3  Duplicates: 0  Warnings: 0mysql> select * from user;    ##查看表内容+----+--------+-------+-------+| id | name   | score | hobby |+----+--------+-------+-------+|  1 | test01 |    88 |     1 ||  2 | stu01  |    99 |     2 ||  3 | wangwu |    77 |     3 |+----+--------+-------+-------+3 rows in set (0.00 sec)mysql> create table hob(     ##创建hob表        -> id int(2) not null primary key,        -> hob_name varchar(10) not null);Query OK, 0 rows affected (0.00 sec)mysql> desc hob;   ##查看表结构+----------+-------------+------+-----+---------+-------+| Field    | Type        | Null | Key | Default | Extra |+----------+-------------+------+-----+---------+-------+| id       | int(2)      | NO   | PRI | NULL    |       || hob_name | varchar(10) | NO   |     | NULL    |       |+----------+-------------+------+-----+---------+-------+2 rows in set (0.00 sec)mysql> insert into hob (id,hob_name) values (1,'看书'),(2,'运动'),(3,'听歌');   ##插入表数据Query OK, 3 rows affected (0.00 sec)Records: 3  Duplicates: 0  Warnings: 0mysql> select * from hob;   ##查看表内容+----+----------+| id | hob_name |+----+----------+|  1 | 看书     ||  2 | 运动     ||  3 | 听歌     |+----+----------+3 rows in set (0.00 sec)mysql> select * from user inner join hob on user.hobby=hob.id;   ##关联user和hob两张表+----+--------+-------+-------+----+----------+| id | name   | score | hobby | id | hob_name |+----+--------+-------+-------+----+----------+|  1 | test01 |    88 |     1 |  1 | 看书     ||  2 | stu01  |    99 |     2 |  2 | 运动     ||  3 | wangwu |    77 |     3 |  3 | 听歌     |+----+--------+-------+-------+----+----------+3 rows in set (0.00 sec)mysql> select user.name,hob.hob_name from user inner join hob on user.hobby=hob.id;##去除其他内容显示name和hob_name内容+--------+----------+| name   | hob_name |+--------+----------+| test01 | 看书     || stu01  | 运动     || wangwu | 听歌     |+--------+----------+3 rows in set (0.00 sec)mysql> select u.name,h.hob_name from user u inner join hob h on u.hobby=h.id; ##设置简易名称+--------+----------+| name   | hob_name |+--------+----------+| test01 | 看书     || stu01  | 运动     || wangwu | 听歌     |+--------+----------+3 rows in set (0.00 sec)mysql> create view view_user as select u.name,h.hob_name from user u inner join hob h on u.hobby##创建视图Query OK, 0 rows affected (0.00 sec)mysql> select * from view_user;  ##查看视图+--------+----------+| name   | hob_name |+--------+----------+| test01 | 看书     || stu01  | 运动     || wangwu | 听歌     |+--------+----------+3 rows in set (0.00 sec)mysql> update user set hobby=3 where name='test01';  ##修改user表中内容Query OK, 1 row affected (0.00 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> select * from view_user;   ##查看视图，即视图就是表的一个链接+--------+----------+| name   | hob_name |+--------+----------+| stu01  | 运动     || test01 | 听歌     || wangwu | 听歌     |+--------+----------+3 rows in set (0.00 sec)

5，全文索引，组合索引

mysql> select * from info;     ##查看表内容+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 |+----+----------+----------+-----+2 rows in set (0.00 sec)mysql> show index from info;    ##查看表的索引+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY    |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          0 | index_name |            1 | name        | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+2 rows in set (0.00 sec)mysql> create fulltext index full_addr on info (address);      ##以address创建全文索引Query OK, 0 rows affected, 1 warning (0.07 sec)Records: 0  Duplicates: 0  Warnings: 1mysql> show index from info;  ##查看表索引+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| info  |          0 | PRIMARY    |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          0 | index_name |            1 | name        | A         |           2 |     NULL | NULL   |      | BTREE      |         |               || info  |          1 | full_addr  |            1 | address     | NULL      |           2 |     NULL | NULL   | YES  | FULLTEXT   |         |               |+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+3 rows in set (0.00 sec)mysql> select * from user;     ##查看user表内容+----+--------+-------+-------+| id | name   | score | hobby |+----+--------+-------+-------+|  1 | test01 |    88 |     3 ||  2 | stu01  |    99 |     2 ||  3 | wangwu |    77 |     3 |+----+--------+-------+-------+3 rows in set (0.00 sec)mysql> create index index_name_score on user (name,score);    ##创建name和score的组合索引Query OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show index from user;   ##查看表索引+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name         | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| user  |          0 | PRIMARY          |            1 | id          | A         |           3 |     NULL | NULL   |      | BTREE      |         |               || user  |          1 | index_score      |            1 | score       | A         |           3 |     NULL | NULL   |      | BTREE      |         |               || user  |          1 | index_name_score |            1 | name        | A         |           3 |     NULL | NULL   |      | BTREE      |         |               || user  |          1 | index_name_score |            2 | score       | A         |           3 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+4 rows in set (0.00 sec)

事务实操

1，开启事务，往表中插入数据

mysql> select * from info;           ##查看表内容数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 |+----+----------+----------+-----+2 rows in set (0.00 sec)mysql> insert into info (name,address,age) values ('wangwu','hangzhou',30)；        ##插入数据mysql> begin;                             ##开启事务Query OK, 0 rows affected (0.00 sec)mysql> insert into info (name,address,age) values ('zhaoliu','hangzhou',31);  ##插入数据Query OK, 1 row affected (0.00 sec)mysql> savepoint a;                 ##设置保存节点aQuery OK, 0 rows affected (0.00 sec)mysql> select * from info;         ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  4 | zhaoliu  | hangzhou |  31 |+----+----------+----------+-----+4 rows in set (0.00 sec)mysql> insert into info (name,address,age) values ('tianqi','hangzhou',32);  ##继续插入数据Query OK, 1 row affected (0.00 sec)mysql> savepoint b;                  ##设置保存节点bQuery OK, 0 rows affected (0.00 sec)mysql> insert into info (name,address,age) values ('heiba','hangzhou',32);      ##继续插入数据Query OK, 1 row affected (0.00 sec)mysql> select * from info;           ##查看表内容+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  4 | zhaoliu  | hangzhou |  31 ||  5 | tianqi   | hangzhou |  32 ||  6 | heiba    | hangzhou |  32 |+----+----------+----------+-----+6 rows in set (0.00 sec)

2，利用另一个终端查看是否成功插入

[root@master2 ~]# mysql -uroot -p         ##进入数据库Enter password:                                      ##输入密码Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> use school;   ##使用数据库Reading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -ADatabase changedmysql> select * from info;   ##查看表内容，此时并没有提交+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 |+----+----------+----------+-----+3 rows in set (0.00 sec)

3，使用回滚，返回保存的节点

mysql> rollback to b;    ##利用回滚到保存节点bQuery OK, 0 rows affected (0.00 sec)mysql> select * from info;   ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  4 | zhaoliu  | hangzhou |  31 ||  5 | tianqi   | hangzhou |  32 |+----+----------+----------+-----+5 rows in set (0.00 sec)mysql> rollback to a;  ##回滚到保存节点aQuery OK, 0 rows affected (0.00 sec)mysql> select * from info;   ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  4 | zhaoliu  | hangzhou |  31 |+----+----------+----------+-----+4 rows in set (0.00 sec)mysql> rollback;     ##回滚到初始，退出事务状态Query OK, 0 rows affected (0.00 sec)mysql> select * from info;  ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 |+----+----------+----------+-----+3 rows in set (0.00 sec)

4，使用commit提交事务

mysql> begin;    ##开启事务Query OK, 0 rows affected (0.00 sec)mysql> insert into info (name,address,age) values ('heiba','hangzhou',32);  ##插入数据Query OK, 1 row affected (0.00 sec)mysql> commit;   ##提交事务Query OK, 0 rows affected (0.00 sec)mysql> select * from info;  ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  7 | heiba    | hangzhou |  32 |+----+----------+----------+-----+4 rows in set (0.00 sec)

5，使用另一个终端查看

mysql> select * from info;   ##查看表数据+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  7 | heiba    | hangzhou |  32 |+----+----------+----------+-----+4 rows in set (0.00 sec)

6，另一种事务的操作方式

mysql> set autocommit=0;   ##设置不自动提交事务Query OK, 0 rows affected (0.00 sec)mysql> update info set address='beijing' where name='heiba';  ##修改表数据Query OK, 1 row affected (0.00 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> select * from info;   ##查看表信息+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  7 | heiba    | beijing  |  32 |+----+----------+----------+-----+4 rows in set (0.00 sec)##另一个终端查看mysql> select * from info;  ##查看表信息，并没有修改+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  7 | heiba    | hangzhou |  32 |+----+----------+----------+-----+4 rows in set (0.00 sec)mysql> set autocommit=1;   ##开启自动提交事务Query OK, 0 rows affected (0.00 sec)##另一个终端查看mysql> select * from info;   ##查看表数据，此时就已经修改+----+----------+----------+-----+| id | name     | address  | age |+----+----------+----------+-----+|  1 | zhangsan | beijing  |  20 ||  2 | lisi     | shanghai |  22 ||  3 | wangwu   | hangzhou |  30 ||  7 | heiba    | beijing  |  32 |+----+----------+----------+-----+4 rows in set (0.00 sec)

存储引擎MyLSAM和InnoDB

1，查看系统默认存储引擎

mysql> show engines;   ##查看默认存储引擎innodb+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |mysql> show create table info;   ##查看创建的表的存储引擎innodb| info  | CREATE TABLE "info" (    "id" int(4) NOT NULL AUTO_INCREMENT,    "name" varchar(10) NOT NULL,    "address" varchar(50) DEFAULT 'nanjing',    "age" int(3) NOT NULL,    PRIMARY KEY ("id"),    UNIQUE KEY "index_name" ("name"),    FULLTEXT KEY "full_addr" ("address")) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8

2，修改MySQL配置文件，设置默认的存储引擎

[root@localhost ~]# vim /etc/my.cnf ##修改配置文件[mysqld]user = mysqlbasedir = /usr/local/mysqldatadir = /usr/local/mysql/dataport = 3306character_set_server=utf8pid-file = /usr/local/mysql/mysql.pidsocket = /usr/local/mysql/mysql.sockserver-id = 1default-storage-engine=Myisam   ##添加默认存储引擎为Myisam[root@master2 ~]# systemctl restart mysqld.service ##重启MySQL服务

3，进入数据库

[root@master2 ~]# mysql -uroot -p   ##进入数据库Enter password:    ##输入密码mysql> use school;    ##使用数据库Reading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -ADatabase changedmysql> create table a ( id int );    ##创建一个a表Query OK, 0 rows affected (0.00 sec)mysql> show create table a;   ##查看表默认的存储引擎Myisam+-------+-------------------------------------------------------------------------------------+| Table | Create Table                                                                        |+-------+-------------------------------------------------------------------------------------+| a     | CREATE TABLE "a" (    "id" int(11) DEFAULT NULL) ENGINE=MyISAM DEFAULT CHARSET=utf8 |+-------+-------------------------------------------------------------------------------------+1 row in set (0.00 sec)mysql> alter table a engine=innodb;  ##修改表的存储引擎为innodbQuery OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show create table a;  ##查看表的存储引擎innodb+-------+-------------------------------------------------------------------------------------+| Table | Create Table                                                                        |+-------+-------------------------------------------------------------------------------------+| a     | CREATE TABLE "a" (    "id" int(11) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8 |+-------+-------------------------------------------------------------------------------------+1 row in set (0.00 sec)