4.1 create and drop database

C:\Users\admin> mysql -h localhost -u root -pmysql

mysql: [Warning] Using a password on the command line interface can be insecure.

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 3

Server version: 5.7.14 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, 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> show databases;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| test               |

+--------------------+

5 rows in set (0.00 sec)

mysql> create database example;         #create database

Query OK, 1 row affected (0.04 sec)

mysql> show databases;                # 显示 databases

+--------------------+

| Database           |

+--------------------+

| information_schema |

| example            |

| mysql              |

| performance_schema |

| sys                |

| test               |

+--------------------+

6 rows in set (0.00 sec)

mysql> drop database example;              #drop database;

Query OK, 0 rows affected (0.04 sec)

mysql> show databases;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| test               |

+--------------------+

5 rows in set (0.00 sec)

mysql> create database mysql;

ERROR 1007 (HY000): Can't create database 'mysql'; database exists

mysql> create database mydata;

Query OK, 1 row affected (0.01 sec)

4.2 存储引擎

mysql> show engines \G

*************************** 1. row ***************************

      Engine: InnoDB

     Support: DEFAULT

     Comment: Supports transactions, row-level locking, and foreign keys

Transactions: YES

          XA: YES

  Savepoints: YES

*************************** 2. row ***************************

      Engine: MRG_MYISAM

     Support: YES

     Comment: Collection of identical MyISAM tables

Transactions: NO

          XA: NO

  Savepoints: NO

*************************** 3. row ***************************

      Engine: MEMORY

     Support: YES

     Comment: Hash based, stored in memory, useful for temporary tables

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: MyISAM

     Support: YES

     Comment: MyISAM storage engine

Transactions: NO

          XA: NO

  Savepoints: NO

*************************** 6. row ***************************

      Engine: CSV

     Support: YES

     Comment: CSV storage engine

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: PERFORMANCE_SCHEMA

     Support: YES

     Comment: Performance Schema

Transactions: NO

          XA: NO

  Savepoints: NO

*************************** 9. row ***************************

      Engine: FEDERATED

     Support: NO

     Comment: Federated MySQL storage engine

Transactions: NULL

          XA: NULL

  Savepoints: NULL

9 rows in set (0.00 sec)

mysql>

4.2.1 InnoDB engine

InnoDB 是 mysql 数据库中的存储引擎 ,innodb 给 mysql 的表提供了事务，回滚，崩溃修复能力，多版本并发控制的事务安全

(1)     Innodb 那个。存储引擎支持自动增长列 auto_increment.

(2)     Innodb 存储引擎支持外键 (foreign key)

(3)     Innodb 存储引擎，创建的表的表结构在 .frm 文件中，数据和索引存储在 innodb_data_home_dir 和 innodb_data_file_path 定义的表空间

(4)     Innodb 存储引擎的 缺点 是读写效率稍差，占用的数据空间相对较大。

4.2.2 MyISAM engine

MyISAM 是 mysql 中常见的存储引擎

MyISAM 存储引擎的表存储成三个文件。文件的名字与表名相同，扩展名包括 frm,MYD,MYI,

. 其中 frm 为扩展名的文件存储表的结构； MYD(MYData) 为扩展名的文件存储数据， MYI(MYindex) 为扩展名的文件存储引擎

MyISAM 存储引擎的优势在于占用空间小，处理速度快。缺点是不支持事务的完整性和并发性。

4.2.3 MEMORY

特殊存储引擎 , 表结构在 disk 上，数据在内存中。

Memory 表的大小受到显示，表的大小取决于两个参数 max_rows 和 max_heap_table_size

4.2.4 engines 的选择 .