Mysql如何创建数据库
小编给大家分享一下MySQL如何创建数据库，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
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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.
特性 | InnoDB | MyISAM | MEMORY |
事务安全 | 支持 | 无 | 无 |
存储限制 | 64TB | 有 | 有 |
空间使用 | 高 | 低 | 低 |
内存使用 | 高 | 低 | 高 |
插入数据的速度 | 低 | 高 | 高 |
对外键的迟滞 | 支持 | 无 | 无 |
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