[TOC]
## 一、 创建数据库
### 1.创建数据库语法：`create database [if not exists] db_name [create_specification];`
基本语法创建数据库 mytest，例：
```sql
mysql> create database mytest;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| mytest |
| performance_schema |
| school |
| school_01 |
| shop |
| sys |
+--------------------+
8 rows in set (0.00 sec)
```
#### a、可选项 `if not exists`
创建数据库时若加上选项 `if not exists` ，如果这个数据库**没有存在**就顺利创建：
```sql
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| school_01 |
| shop |
| sys |
+--------------------+
7 rows in set (0.00 sec)
mysql> create database if not exists test2;
Query OK, 1 row affected (0.00 sec)
```
创建数据库时若加上选项 `if not exists` ，如果**已经存在**这个数据库就不会创建，并给出一个警告 warning：
```sql
mysql> create database if not exists test2;
Query OK, 1 row affected, 1 warning (0.00 sec)
```
查看给出的警告：
```sql
mysql> show warnings;
+-------+------+------------------------------------------------+
| Level | Code | Message |
+-------+------+------------------------------------------------+
| Note | 1007 | Can't create database 'test2'; database exists |
+-------+------+------------------------------------------------+
1 row in set (0.00 sec)
```
创建数据库时若不加选项 `if not exists` ，如果这个数据库没有存在就顺利创建；如果已经存在这个数据库就会创建失败，并报错提示：
```sql
mysql> create database test3;
Query OK, 1 row affected (0.00 sec)
mysql> create database test3;
ERROR 1007 (HY000): Can't create database 'test3'; database exists
```
#### b、可选项 `create_specification`
数据库创建选项 create_specification 有两个待设置的内容：
1. `character set`：字符集，定义了字符以及字符的编码。常见的如 latin1、gbk、utf8、utf8mb4 等。
2. `collate`：字符校对规则，字符序，定义了字符的比较规则。它们以其相关的字符集名开始，通常包括一个语言名，并且以 `_ci`（大小写不敏感）、`_cs`（大小写敏感）或 `_bin`（二元法，二进制编码）结束。建议使用 bin 类型，相对更准确。
例，创建数据库 mytest 时设置 character set ：
```sql
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| school_01 |
| shop |
| sys |
+--------------------+
7 rows in set (0.00 sec)
mysql> create database mytest character set utf8;
Query OK, 1 row affected (0.00 sec)
mysql> show create database mytest;
+----------+-----------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------+
| mytest | CREATE DATABASE `mytest` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------------------+
1 row in set (0.00 sec)
```
例，创建数据库 test2时设置 character set 和 collate ：
```sql
mysql> create database test2 character set utf8 collate utf8_bin;
Query OK, 1 row affected (0.00 sec)
mysql> show create database test2;
+----------+---------------------------------------------------------------------------------+
| Database | Create Database |
+----------+---------------------------------------------------------------------------------+
| test2 | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */ |
+----------+---------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```
## 二、修改数据库选项
**基本语法为：** `alter database db_name [alter_specification] `
例如，修改数据库 test2 的字符集为 utf8 ：
```sql
mysql> show create database test2;
+----------+------------------------------------------------------------------+
| Database | Create Database |
+----------+------------------------------------------------------------------+
| test2 | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> alter database test2 character set utf8;
Query OK, 1 row affected (0.00 sec)
mysql> show create database test2;
+----------+----------------------------------------------------------------+
| Database | Create Database |
+----------+----------------------------------------------------------------+
| test2 | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+----------------------------------------------------------------+
1 row in set (0.00 sec)
```
例如，修改数据库 test2 的字符集为 gbk 和字符序为 gbk _bin ：
```sql
mysql> alter database test2 character set gbk collate gbk_bin;
Query OK, 1 row affected (0.00 sec)
mysql> show create database test2;
+----------+-------------------------------------------------------------------------------+
| Database | Create Database |
+----------+-------------------------------------------------------------------------------+
| test2 | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET gbk COLLATE gbk_bin */ |
+----------+-------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```
## 三、删除数据库
### 1.删除数据库语法：`drop database db_name;`
例如，删除数据库 mytest ：
```sql
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| mytest |
| performance_schema |
| school |
| school_01 |
| shop |
| sys |
+--------------------+
8 rows in set (0.00 sec)
mysql> drop database mytest;
Query OK, 0 rows affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| school_01 |
| shop |
| sys |
+--------------------+
7 rows in set (0.00 sec)
```
