MySQL 库的操作
1. 创建与删除数据库
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
- db_name：数据库名
- IF NOT EXISTS：如果要创建的数据库不存在就创建，存在就不创建（避免报错）
- 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
创建名为db1的数据库：create database db1：
mysql> show databases; +---------------------+ | Database | +---------------------+ | db1 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +---------------------+ 6 rows in set (0.01 sec)当我们创建数据库没有指定字符集和校验规则时，系统会使用默认字符集和校验规则。我的系统默认字符集是utf8mb4，默认校验规则是utf8mb4_0900_ai_ci（如下图所示）。
mysql> show create database db1; +----------+----------------------------------------------------------------------------------------------------------------------------------+ | Database | Create Database | +----------+----------------------------------------------------------------------------------------------------------------------------------+ | db1 | CREATE DATABASE `db1` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ | +----------+----------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)删除数据库
语法：drop database db_name
删除名为db1的数据库：drop database db1：
mysql> show databases; +--------------------+ | Database | +--------------------+ | db1 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 6 rows in set (0.01 sec) mysql> drop database db1; Query OK, 0 rows affected (0.01 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 5 rows in set (0.01 sec)总结：创建数据库：create database db_name；删除数据库：drop database db_name。
创建数据库的本质，就是在某条特定的路径下创建一个目录。删除数据库的本质，就是删除在某条特定的路径下删除一个目录。
注意：删除数据库会连同里面的所有数据表一起删除，建议不要随意删除。
2. 数据库编码
创建数据库时，涉及两个编码集：
- 数据库编码集：数据库存储数据时使用的编码格式
- 数据库校验集：数据库读取数据时使用的编码格式
核心原则：数据库对数据做任何操作，都必须保证操作和编码保持一致。
查看系统默认字符集以及校验规则：
show variables like 'character_set_database';查看系统默认字符集
show variables like 'collation_database';查看系统默认校验规则
我的系统默认字符集是 utf8mb4，默认校验规则是 utf8mb4_0900_ai_ci。
mysql> show variables like 'character_set_database'; +------------------------+---------+ | Variable_name | Value | +------------------------+---------+ | character_set_database | utf8mb4 | +------------------------+---------+ 1 row in set (0.01 sec) mysql> show variables like 'collation_database'; +--------------------+-------------------+ | Variable_name | Value | +--------------------+-------------------+ | collation_database | utf8mb4_0900_ai_ci | +--------------------+-------------------+ 1 row in set (0.01 sec)实际上，目前整个数据库的校验规则都是 utf8mb4_09：
mysql> show variables like 'collation_%'; +----------------------+-------------------+ | Variable_name | Value | +----------------------+-------------------+ | collation_connection | utf8mb4_0900_ai_ci | | collation_database | utf8mb4_0900_ai_ci | | collation_server | utf8mb4_0900_ai_ci | +----------------------+-------------------+ 3 rows in set (0.01 sec)输入show charset;查看数据库支持的所有字符集：
mysql> show charset; +----------+---------------------------------+-------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+---------------------------------+-------------------+--------+ | armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 | | ascii | US ASCII | ascii_general_ci | 1 | | big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 | | binary | Binary pseudo charset | binary | 1 | | cp1250 | Windows Central European | cp1250_general_ci | 1 | | cp1251 | Windows Cyrillic | cp1251_general_ci | 1 | | cp1256 | Windows Arabic | cp1256_general_ci | 1 | | cp1257 | Windows Baltic | cp1257_general_ci | 1 | | cp850 | DOS West European | cp850_general_ci | 1 | | cp852 | DOS Central European | cp852_general_ci | 1 | | cp866 | DOS Russian | cp866_general_ci | 1 | | cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 | | dec8 | DEC West European | dec8_swedish_ci | 1 | | eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 | | euckr | EUC-KR Korean | euckr_korean_ci | 2 | | gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 | | gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 | | gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 | | geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 | | greek | ISO 8859-7 Greek | greek_general_ci | 1 | | hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 | | hp8 | HP West European | hp8_english_ci | 1 | | keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 | | koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 | | koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 | | latin1 | cp1252 West European | latin1_swedish_ci | 1 | | latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 | | latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 | | latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 | | macce | Mac Central European | macce_general_ci | 1 | | macroman | Mac West European | macroman_general_ci | 1 | | sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 | | swe7 | 7bit Swedish | swe7_swedish_ci | 1 | | tis620 | TIS620 Thai | tis620_thai_ci | 1 | | ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 | | ujis | EUC-JP Japanese | ujis_japanese_ci | 3 | | utf16 | UTF-16 Unicode | utf16_general_ci | 4 | | utf16le | UTF-16LE Unicode | utf16le_general_ci | 4 | | utf32 | UTF-32 Unicode | utf32_general_ci | 4 | | utf8mb3 | UTF-8 Unicode | utf8mb3_general_ci | 3 | | utf8mb4 | UTF-8 Unicode | utf8mb4_0900_ai_ci | 4 | +----------+---------------------------------+-------------------+--------+输入show collation;查看数据库支持的校验规则。
创建指定字符集/校验规则的数据库
创建一个使用 utf8mb4 字符集的db2数据库：create database db2 charset=utf8mb4;或者 create database db2 character set utf8mb4;
mysql> create database db2 charset=utf8mb4; Query OK, 1 row affected (0.01 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | db2 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 6 rows in set (0.00 sec)总结：创建一个使用特定字符集的数据库：create database db_name charset=charset_name;或者create database db_name character set utf8mb4;。
创建使用 utf8mb4_0900_ai_ci 校验规则的 db3 数据库：create database db3 collate utf8mb4_0900_ai_ci;
mysql> create database db3 collate utf8mb4_0900_ai_ci; Query OK, 1 row affected (0.01 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | db2 | | db3 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 7 rows in set (0.00 sec)总结：创建一个使用特定校验规则的数据库：create database db_name collate collate_name。
校验规则的区别演示
创建一个校验规则为 utf8mb4_0900_ai_ci（不区分大小写）的数据库：create database db_name collate utf8mb4_0900_ai_ci;
mysql> create database databasel collate utf8mb4_0900_ai_ci; Query OK, 1 row affected (0.01 sec) mysql> use databasel; Database changed mysql> create table test(name varchar(20)); Query OK, 0 rows affected (0.03 sec) mysql> insert into test values('a'); Query OK, 1 row affected (0.01 sec) mysql> insert into test values('A'); Query OK, 1 row affected (0.01 sec) mysql> insert into test values('b'); Query OK, 1 row affected (0.01 sec) mysql> insert into test values('B'); Query OK, 1 row affected (0.01 sec)不区分大小写时的排序和查询结果：
mysql> use database1; Database changed mysql> select * from test order by name; +-------+ | name | +-------+ | a | | A | | b | | B | +-------+ 4 rows in set (0.00 sec)创建一个校验规则为 utf8mb4_bin（区分大小写）的数据库：create database db_name collate utf8mb4_bin;
mysql> create database database2 collate utf8mb4_bin; Query OK, 1 row affected (0.01 sec) mysql> use database2; Database changed mysql> create table test(name varchar(20)); Query OK, 0 rows affected (0.03 sec) mysql> insert into test values('a'); Query OK, 1 row affected (0.01 sec) mysql> insert into test values('A'); Query OK, 1 row affected (0.00 sec) mysql> insert into test values('b'); Query OK, 1 row affected (0.01 sec) mysql> insert into test values('B'); Query OK, 1 row affected (0.01 sec)区分大小写时的排序和查询结果：
mysql> use database2; Database changed mysql> select * from test order by name; +-------+ | name | +-------+ | A | | B | | a | | b | +-------+ 4 rows in set (0.00 sec)结论：校验规则不同，查询和排序的结果也会不同。
为什么要在数据库层面设置字符集和校验规则？为了能够存储任意字符集和校验规则的表格。实际开发中，如果没有特殊需求，按数据库默认的字符集和校验规则创建即可，需要指定时再单独配置。
3. 操作数据库
查看所有数据库：show databases;
mysql> show databases; +--------------------+ | Database | +--------------------+ | database1 | | database2 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 7 rows in set (0.00 sec)查看数据库的创建语句：show create database db_name;
mysql> show create database database1; +-----------+----------------------------------------------------------------------------------------------------------------------------------+ | Database | Create Database | +-----------+----------------------------------------------------------------------------------------------------------------------------------+ | database1 | CREATE DATABASE `database1` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ | +-----------+----------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)!40100 表示：如果当前使用的mysql版本是大于401，就执行后续的语句，后面就是默认的字符集和校验规则，即 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N'，这就是默认字符集和校验规则。
确认当前正在使用的数据库：select database();
mysql> select database(); +------------+ | database() | +------------+ | database1 | +------------+ 1 row in set (0.00 sec)修改数据库，语法：
ALTER DATABASE db_name [alter_spacification [,alter_spacification]...] alter_spacification：
[DEFAULT] CHARACTER SET charset_name
[DEFAULT] COLLATE collation_name
查看表中的字段：desc 表名;
mysql> desc test; +-------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | +-------+-------------+------+-----+---------+-------+ 1 row in set (0.01 sec)4. 数据库的备份与还原
备份整个数据库 —— 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：将数据库 database1 备份到当前路径下的 database1.sql 文件中：
root@hcss-ecs-3ea8:/home/xayy/MYSQL# mysqldump -P3306 -uroot -p -B database1 > database1.sql Enter password: root@hcss-ecs-3ea8:/home/xayy/MYSQL# ls database1.sql备份文件中的内容：将历史上对 database1 数据库执行过的所有有效操作都保存了下来。
-- MySQL dump 10.13 Distrib 8.0.46, for Linux (x86_64) -- -- Host: localhost Database: database1 -- ------------------------------------------------------ -- Server version 8.0.46 /*!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 */; /*!50503 SET NAMES utf8mb4 */; /*!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: `database1` -- CREATE DATABASE /*!32312 IF NOT EXISTS*/ `database1` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */; USE `database1`; -- -- Table structure for table `test` -- DROP TABLE IF EXISTS `test`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!50503 SET character_set_client = utf8mb4 */; CREATE TABLE `test` ( `name` varchar(20) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `test` -- LOCK TABLES `test` WRITE; /*!40000 ALTER TABLE `test` DISABLE KEYS */; INSERT INTO `test` VALUES ('a'),('A'),('b'),('B'); /*!40000 ALTER TABLE `test` 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 2026-05-02 16:05:57还原 —— 语法：source 文件路径
mysql> show databases; +--------------------+ | Database | +--------------------+ | database2 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+ 6 rows in set (0.00 sec) mysql> source /home/xay/MYSQL/database1.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, 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 (0.02 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.01 sec) Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 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) mysql> show databases; +--------------------+ | Database | +--------------------+ | database1 | | database2 | | helloworld | | information_schema | | mysql | | performance_schema | | sys | +--------------------+备份一张或多张表（不备份整个数据库）：mysqldump -u root -p 数据库名 表名1 表名2 > 文件路径/文件名
同时备份多个数据库：mysqldump -u root -p -B 数据库名1 数据库名2 ... > 数据库存放路径
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
- 先手动创建空的数据库
- 使用 use 数据库名; 选中它
- 再执行 source 恢复
查看数据库的连接情况：show processlist;
mysql> show processlist; +----+-----------------+-----------+------------+---------+------+-------------------+------------------+ | Id | User | Host | db | Command | Time | State | Info | +----+-----------------+-----------+------------+---------+------+-------------------+------------------+ | 7 | event_scheduler | localhost | NULL | Daemon | 1625443 | Waiting on empty queue | NULL | | 30 | root | localhost | database1 | Query | 0 | init | show processlist | +----+-----------------+-----------+------------+---------+------+-------------------+------------------+ 2 rows in set, 1 warning (0.00 sec)