【MySql-Command】-DataBase

创建数据库


注意:创建数据库之前要先连接Mysql服务器

命令:create database <数据库名>

例1:建立一个名为xhkdb的数据库
  
 mysql> create database mydb;

例2:创建数据库并分配用户

①CREATE DATABASE 数据库名;

②GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP,ALTER ON 数据库名.* TO 数据库名@localhost IDENTIFIED BY '密码';

③SET PASSWORD FOR '数据库名'@'localhost' = OLD_PASSWORD('密码');

依次执行3个命令完成数据库创建。
注意:中文 “密码”和“数据库”是户自己需要设置的
======================================================

显示数据库

命令:show databases (注意:最后有个s)
mysql> show databases;

注意:为了不再显示的时候乱码,要修改数据库默认编码。以下以GBK编码页面为例进行说明:

1、修改MYSQL的配置文件:
my.ini里面修改default-character-set=gbk
2、代码运行时修改:
   ①Java代码:jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=gbk
   ②PHP代码:header("Content-Type:text/html;charset=gb2312");
   ③C语言代码:int mysql_set_character_set( MYSQL * mysql, char * csname);

该函数用于为当前连接设置默认的字符集。
字符串csname指定了1个有效的字符集名称。
连接校对成为字符集的默认校对。该函数的工作方式与SET NAMES语句类似
但它还能设置mysql- > charset的值,从而影响了由mysql_real_escape_string() 设置的字符集。

删除数据库

命令:drop database <数据库名>
例如:删除名为 xhkdb的数据库
mysql> drop database xhkdb;

例子1:删除一个已经确定存在的数据库
   mysql> drop database drop_database;
   Query OK, 0 rows affected (0.00 sec)

例子2:删除一个不确定存在的数据库
   mysql> drop database drop_database;
   ERROR 1008 (HY000): Can't drop database 'drop_database'; database doesn't exist
      //发生错误,不能删除'drop_database'数据库,该数据库不存在。
   mysql> drop database if exists drop_database;
   Query OK, 0 rows affected, 1 warning (0.00 sec)//产生一个警告说明此数据库不存在
   mysql> create database drop_database;
   Query OK, 1 row affected (0.00 sec)
   mysql> drop database if exists drop_database;//if exists 判断数据库是否存在,不存在也不产生错误
   Query OK, 0 rows affected (0.00 sec)

连接数据库

命令: use <数据库名>

例如:如果xhkdb数据库存在,尝试存取它:
      mysql> use xhkdb;
屏幕提示:Database changed

use 语句可以通告MySQL把db_name数据库作为默认(当前)数据库使用,用于后续语句。
该数据库保持为默认数据库,直到语段的结尾,或者直到发布一个不同的USE语句:
   mysql> USE db1;
   mysql> SELECT COUNT(*) FROM mytable;   # selects from db1.mytable
   mysql> USE db2;
   mysql> SELECT COUNT(*) FROM mytable;   # selects from db2.mytable

使用USE语句为一个特定的当前的数据库做标记,不会阻碍您访问其它数据库中的表。
下面的例子可以从db1数据库访问作者表,并从db2数据库访问编辑表:
   mysql> USE db1;
   mysql> SELECT author_name,editor_name FROM author,db2.editor
       ->        WHERE author.editor_id = db2.editor.editor_id;

USE语句被设立出来,用于与Sybase相兼容。

有些网友问到,连接以后怎么退出。其实,不用退出来,use 数据库后,使用show databases就能查询所有数据库,如果想跳到其他数据库,用  use 其他数据库名字就可以了。
命令:mysql> select database();

当前选择的数据库

命令:mysql> select database();

*SELECT命令类似于其他编程语言里的print或者write
你可以用它来显示一个字符串、数字、数学表达式的结果等等

1.显示MYSQL的版本
mysql> select version(); 
+-----------------------+ 
| version()             | 
+-----------------------+ 
| 6.0.4-alpha-community | 
+-----------------------+ 
1 row in set (0.02 sec) 

2. 显示当前时间
mysql> select now(); 
+---------------------+ 
| now()               | 
+---------------------+ 
| 2009-09-15 22:35:32 | 
+---------------------+ 
1 row in set (0.04 sec) 

3. 显示年月日
SELECT DAYOFMONTH(CURRENT_DATE); 
+--------------------------+ 
| DAYOFMONTH(CURRENT_DATE) | 
+--------------------------+ 
|                       15 | 
+--------------------------+ 
1 row in set (0.01 sec) 
  
SELECT MONTH(CURRENT_DATE); 
+---------------------+ 
| MONTH(CURRENT_DATE) | 
+---------------------+ 
|                   9 | 
+---------------------+ 
1 row in set (0.00 sec) 
  
SELECT YEAR(CURRENT_DATE); 
+--------------------+ 
| YEAR(CURRENT_DATE) | 
+--------------------+ 
|               2009 | 
+--------------------+ 
1 row in set (0.00 sec) 

4. 显示字符串
mysql> SELECT "welecome to my blog!"; 
+----------------------+ 
| welecome to my blog! | 
+----------------------+ 
| welecome to my blog! | 
+----------------------+ 
1 row in set (0.00 sec) 

5. 当计算器用
select ((4 * 4) / 10 ) + 25; 
+----------------------+ 
| ((4 * 4) / 10 ) + 25 | 
+----------------------+ 
|                26.60 | 
+----------------------+ 
1 row in set (0.00 sec) 

6. 串接字符串
select CONCAT(f_name, " ", l_name) 
AS Name 
from employee_data 
where title = 'Marketing Executive'; 
+---------------+ 
| Name          | 
+---------------+ 
| Monica Sehgal | 
| Hal Simlai    | 
| Joseph Irvine | 
+---------------+ 
3 rows in set (0.00 sec) 
注意:这里用到CONCAT()函数,用来把字符串串接起来。
另外,我们还用到以前学到的AS给结果列'CONCAT(f_name, " ", l_name)'起了个假名
### MCP MySQL Server Configuration and Management #### Overview of MCP MySQL Server Setup For configuring an MCP (Multi-Cloud Platform) environment with a MySQL server, the setup involves ensuring that all necessary configurations are correctly applied to integrate MySQL as part of the data storage solution. In scenarios where applications like Nacos need to connect to a MySQL database, it is crucial to ensure proper initialization and configuration. #### Initialization of MySQL Database for Application Integration When initializing a MySQL database specifically for application integration such as switching from default settings to using MySQL, one can modify `application.properties` or configure during Docker startup[^1]. This ensures that the application connects to the correct MySQL instance configured within the MCP environment. #### Schema Creation for Application Data Persistence To avoid issues related to no datasource exceptions when deploying services on platforms like Nacos via Docker while aiming at persisting data into MySQL, creating databases and tables beforehand is essential. The SQL script located at `D:\software\nacos\nacos-server-2.3.1\conf\mysql-schema.sql` serves this purpose by providing commands needed for setting up schemas required by Nacos[^2]. #### Troubleshooting Common Issues During Deployment In cases similar to those described in experiences involving deployment challenges—such as encountering errors due to missing database creation steps—it becomes evident how critical these preparatory actions are before attempting service deployments. Ensuring that both the database exists along with its schema helps prevent common pitfalls associated with connectivity problems between containers running inside Docker environments and external databases[^3]. ```sql -- Example command to create a new database named 'mcp_db' CREATE DATABASE mcp_db; USE mcp_db; SOURCE D:/software/nacos/nacos-server-2.3.1/conf/mysql-schema.sql; ```
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