数据库（三）：存储引擎

进击のpython

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数据库——存储引擎

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上一节在表的操作的最后一点，提到了一个设置存储引擎

那什么是存储引擎呢？存储引擎能用来干什么？

这就是本小节所要研究的问题了

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存储引擎

库就是创建了一个文件夹，在文件夹里存储的文件就叫表

那根据生活常识应该知道，不同的文件的格式是不一样的

文字的就是txt，视频的就是MP4，音乐的就是MP3... ...

那对于表来说也应该有不同的类型用以存储不同的信息

那这个搜索引擎，就是表的类型

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MySQL支持的引擎

有个语句可以帮助你知道有什么引擎

show engines G

mysql> show engines G
*************************** 1. row ***************************
      Engine: FEDERATED
     Support: NO
     Comment: Federated MySQL storage engine
Transactions: NULL
          XA: NULL
  Savepoints: NULL
*************************** 2. row ***************************
      Engine: MRG_MYISAM
     Support: YES
     Comment: Collection of identical MyISAM tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 3. row ***************************
      Engine: MyISAM
     Support: YES
     Comment: MyISAM storage engine
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 4. row ***************************
      Engine: BLACKHOLE
     Support: YES
     Comment: /dev/null storage engine (anything you write to it disappears)
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 5. row ***************************
      Engine: CSV
     Support: YES
     Comment: CSV storage engine
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 6. row ***************************
      Engine: MEMORY
     Support: YES
     Comment: Hash based, stored in memory, useful for temporary tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 7. row ***************************
      Engine: ARCHIVE
     Support: YES
     Comment: Archive storage engine
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 8. row ***************************
      Engine: InnoDB
     Support: DEFAULT
     Comment: Supports transactions, row-level locking, and foreign keys
Transactions: YES
          XA: YES
  Savepoints: YES
*************************** 9. row ***************************
      Engine: PERFORMANCE_SCHEMA
     Support: YES
     Comment: Performance Schema
Transactions: NO
          XA: NO
  Savepoints: NO
9 rows in set (0.00 sec)

那现在就进行简单的介绍，只是了解！！！！！！

create table e1(id int) engine= innodb;

create table e2(id int) engine= memory;

create table e3(id int) engine= blackhole;

create table e4(id int) engine= myisam;

mysql> create table e1(id int) engine= innodb;
Query OK, 0 rows affected (0.72 sec)

mysql>
mysql> create table e2(id int) engine= memory;
Query OK, 0 rows affected (0.07 sec)

mysql>
mysql> create table e3(id int) engine= blackhole;
Query OK, 0 rows affected (0.13 sec)

mysql>
mysql> create table e4(id int) engine= myisam;
Query OK, 0 rows affected (0.14 sec)

mysql> show tables;
+-------------+
| Tables_in_e |
+-------------+
| e1          |
| e2          |
| e3          |
| e4          |
+-------------+
4 rows in set (0.00 sec)

创建了之后，我们就去文件夹里找一下我们刚才创建的文件

frm后缀的是表结构，ibd 就是 innodb的缩写，所以我们就看出来不是一个表就对应一个文件，那只是你的意淫

e2的搜索引擎是memory，特点是存在内存里的，而不是硬盘，所以没有数据存储，只有表结构

e3的搜索引擎是blackhole，特点是放进去数据就没了，所以也不需要数据存储，只有表结构

e4的搜索引擎是myisam，特点是支持索引，所以除了表结构，数据以外，还多了个索引文件

还是这句话，只是简单了解就行！

那现在就来试试每个引擎下的表的特点

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引擎实例展示

首先先给上面的表格赋值

insert into e1 values(1);

insert into e2 values(1);

insert into e3 values(1);

insert into e4 values(1);

只验证两个具有代表性的引擎：

blackhole

mysql>  select * from e1;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql>
mysql>  select * from e2;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.02 sec)

mysql>
mysql>  select * from e3;
Empty set (0.00 sec)

mysql>
mysql>  select * from e4;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

我们可以看出来e3里面的数据不见了，所以是不是丢进去就没有了~

memory

这是将数据放在内存中，也就是将内存清理后数据就不见了

那怎么办才是将内存进行清理呢？关掉服务再开启就ok了

C:UsersAdministrator>net stop mysql
MySQL 服务正在停止.
MySQL 服务已成功停止。


C:UsersAdministrator>net start mysql
MySQL 服务正在启动 ...
MySQL 服务已经启动成功。


C:UsersAdministrator>mysql
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 1
Server version: 5.6.45 MySQL Community Server (GPL)

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

mysql> use e
Database changed
mysql> select * from e1;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.08 sec)

mysql> select * from e2;
Empty set (0.03 sec)

mysql> select * from e3;
Empty set (0.03 sec)

mysql> select * from e4;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.03 sec)

所以说可以确定memory引擎是将表存在内存的

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