【MySQL--02】库的操作

1.库的操作

1.1创建数据库

语法：

CREATE DATABASE [IF NOT EXISTS] db_name [create_specification [,
create_specification] ...]create_specification:
[DEFAULT] CHARACTER SET charset_name
[DEFAULT] COLLATE collation_name

说明：

• 大写的表示关键字
• [ ]是可选项
• CHARACTER SET：指定数据库采用的字符集
• COLLATE：指定数据库字符集的校验规则

1.2创建数据库的案例

• 创建一个名为db1的数据库

​ create database db1;

说明：当我们创建数据库没有指定字符集和校验规则时，系统使用默认字符集：utf8,校验规则是：utf8_general_ci

• 创建一个使用utf8字符集的db2数据库

create database db2 charset=utf8;

• 创建一个使用utf8字符集，并带校对规则的db3数据库

create database db3 charset=utf8 collate utf8_general_ci;

1.3字符集和校验规则

1.3.1查看系统默认字符集以及校验规则

show variables like 'character_set_database';

show variables like 'collation_database';

1.3.2查看数据库支持的字符集

show charset;

字符集主要是控制用什么语言。比如utf8就可以使用中文。

1.3.3查看数据库支持的字符集校验规则

show collation;

1.3.4 校验规则对数据库的影响

• 不区分大小写 [以下操作为了演示功能所使用的sql语句后面都会讲解]

创建一个数据库，校验规则使用utf8_general_ci[不区分大小写]

create database test1 collate utf8_general_ci;

use test1;

create table person(name varchar(20));

insert into person values('a');
insert into person values('A');
insert into person values('b');
insert into person values('B');

• 区分大小写

创建一个数据库，校验规则使用utf8_bin[区分大小写]

create database test2 collate utf8_bin;

use test2;

create table person(name varchar(20));

insert into person values('a');
insert into person values('A');
insert into person values('b');
insert into person values('B');

• 进行查询

不区分大小写的查询以及结果

mysql> select * from person;
+------+
| name |
+------+
| a    |
| A    |
| b    |
| B    |
+------+
4 rows in set (0.00 sec)
mysql> select * from person where name = 'a';
+------+
| name |
+------+
| a    |
| A    |
+------+
2 rows in set (0.00 sec)

区分大小写的查询以及结果

mysql> select * from person;
+------+
| name |
+------+
| a    |
| A    |
| b    |
| B    |
+------+
4 rows in set (0.00 sec)mysql> select * from person where name = 'a';
+------+
| name |
+------+
| a    |
+------+
1 row in set (0.00 sec)

• 结果排序

不区分大小写排序以及结果

mysql> select * from person order by name asc;
+------+
| name |
+------+
| a    |
| A    |
| b    |
| B    |
+------+
4 rows in set (0.00 sec)
mysql> select * from person order by name desc;
+------+
| name |
+------+
| b    |
| B    |
| a    |
| A    |
+------+
4 rows in set (0.00 sec)

区分大小写排序以及结果

mysql> select * from person order by name asc;
+------+
| name |
+------+
| A    |
| B    |
| a    |
| b    |
+------+
4 rows in set (0.00 sec)mysql> select * from person order by name desc;
+------+
| name |
+------+
| b    |
| a    |
| B    |
| A    |
+------+
4 rows in set (0.00 sec)

1.4操纵数据库

1.4.1查看数据库

show databases;

演示

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| 104_db             |
| mysql              |
| performance_schema |
| sys                |
| test1              |
| test2              |
+--------------------+
7 rows in set (0.00 sec)

1.4.2 删除数据库

drop database [IF EXISTS] [数据库名];

执行删除之后的结果:

• 数据库内部看不到对应的数据库
• 对应的数据库文件夹被删除，级联删除，里面的数据表全部被删

注意：不要随意删除数据库

演示

mysql> drop database test1;
Query OK, 1 row affected (0.09 sec)mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| 104_db             |
| mysql              |
| performance_schema |
| sys                |
| test2              |
+--------------------+
6 rows in set (0.00 sec)

1.4.3显示创建语句

show create database [数据库名];

演示

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)

说明：

• MySQL建议我们关键字使用大写，但是不是必须的。
• 数据库名字的反引号 ``,是为了防止使用的数据库名刚好是关键字。
• /*!40100 DEFAULT .....*/这个不是注释，表示当前MySQL的版本大于4.01版本，就执行这句话。

1.4.4修改数据库

语法：

ALTER DATABASES [数据库名]
[alter_spacification [,alter_spacification]...]alter_spacification:
[DEFAULT] CHARACTER SET charset_name
[DEFAULT] COLLATE collation_name

说明：

• 对数据库的修改主要指的是修改数据库的字符集，校验规则

实例：将test2数据库字符集改成gdk

mysql> alter database test2 charset=gbk;
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 */ |
+----------+---------------------------------------------------------------+
1 row in set (0.00 sec)

1.4.5备份和恢复

1.4.5.1备份

语法：

#mysqldump -P3306 -u root -p 密码 -B 数据库名 > 数据库备份存储的文件路径

示例：将test2库备份到文件(退出连接，在Linux指令行操作)

#mysqldump -P3306 -u root -p123456 -B test2 > D:/test2.sql

这时，可以打开看看test2.sql文件里面的内容，其实可以把我们整个创建数据库，建表，导入数据的语句都装载在这个文件中。

[Lxy@VM-20-12-centos lesson1]$ mysqldump -B test2 > /home/Lxy/mysql/mysql/lesson1/test2.sql
[Lxy@VM-20-12-centos lesson1]$ ll
total 12
-rw-rw-r-- 1 Lxy Lxy 8082 Apr  9 18:11 mysql.sql
-rw-rw-r-- 1 Lxy Lxy 1989 Apr 10 13:11 test2.sql 

我们可以查看test2.sql文件

-- MySQL dump 10.13  Distrib 5.7.41, for Linux (x86_64)
--
-- Host: localhost    Database: test2
-- ------------------------------------------------------
-- Server version	5.7.41/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;--
-- Current Database: `test2`
--CREATE DATABASE /*!32312 IF NOT EXISTS*/ `test2` /*!40100 DEFAULT CHARACTER SET gbk */;USE `test2`;--
-- Table structure for table `person`
--DROP TABLE IF EXISTS `person`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `person` (`name` varchar(20) COLLATE utf8_bin DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
/*!40101 SET character_set_client = @saved_cs_client */;--
-- Dumping data for table `person`
--LOCK TABLES `person` WRITE;
/*!40000 ALTER TABLE `person` DISABLE KEYS */;
INSERT INTO `person` VALUES ('a'),('A'),('b'),('B');
/*!40000 ALTER TABLE `person` ENABLE KEYS */;
UNLOCK TABLES;
/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;-- Dump completed on 2023-04-10 13:11:08

1.4.5.2还原

mysql> source 路径;

演示：我们先删除test2，再还原

mysql> drop database test2;
Query OK, 1 row affected (0.17 sec)mysql> source /home/Lxy/mysql/mysql/lesson1/test2.sql
Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected, 1 warning (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 1 row affected (0.01 sec)Database changed
Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.21 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected (0.02 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 4 rows affected (0.02 sec)
Records: 4  Duplicates: 0  Warnings: 0Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected, 1 warning (0.01 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected (0.02 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.01 sec)Query OK, 0 rows affected (0.02 sec)mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| 104_db             |
| mysql              |
| performance_schema |
| sys                |
| test2              |
+--------------------+
6 rows in set (0.01 sec)

1.4.5.3注意事项

• 如果备份的不是整个数据库，而是其中的一张表，怎么做？

#mysqldump -u root -p 数据库名 表名1 表名2 > 路径

• 同时备份多个数据库

#mysqldump -u root -p -B 数据库名1 数据库名2 .... > 路径

• 如果备份一个数据库时，没有带上-B参数，在恢复数据库时，需要先创建空数据库，然后使用数据库，再使用source来还原

1.4.6查看连接情况

语法

show processlist;

mysql> show processlist;
+----+------+-----------+-------+---------+------+----------+------------------+
| Id | User | Host      | db    | Command | Time | State    | Info             |
+----+------+-----------+-------+---------+------+----------+------------------+
| 11 | root | localhost | test2 | Query   |    0 | starting | show processlist |
+----+------+-----------+-------+---------+------+----------+------------------+
1 row in set (0.00 sec)

show processlist;

mysql> show processlist;
+----+------+-----------+-------+---------+------+----------+------------------+
| Id | User | Host      | db    | Command | Time | State    | Info             |
+----+------+-----------+-------+---------+------+----------+------------------+
| 11 | root | localhost | test2 | Query   |    0 | starting | show processlist |
+----+------+-----------+-------+---------+------+----------+------------------+
1 row in set (0.00 sec)

可以告诉我们当前有哪些用户连接到我们的MySQL，如果查出某个用户不是你正常登录的，很有可能你的数据库被人入侵了。以后大家发现自己数据库比较慢时，可以用这个指令来查看数据库连接情况。