MySQL基本命令

一、结构化语言sql介绍

数据查询语言（DQL：Data Query Language）：其语句，也称为“”“数据检索语言”，用以从表中获得数据，确认数据怎样在应用程序给出，保留字段SELECT是DQL是用的最多的动词。

数据操作语言（DML：Data Manipulation Language ）：其语句包括动词INSERT，UPDATE和DELETE，分别用于添加，修改，删除表中的行。也称为动作查询语言。

数据控制语言（DCL：DataControl Language）：他的语句通过GRANT或者REVOKE获得许可，确定单个用户和用户组对数据库的访问，某些RDBMS可用GRANT和REVOKE控制对表单个列的访问。

数据定义语言（DDL：Data Define Language ）：其语句包括动词CREATE和DROP，在数据库中创建新表或者删除表，为表加入索引，DDL包括许多人数据库目录中获得数据有关的保留字，他是动作查询的一部分。

 数据库中一行是一个实体或者记录

              一列是一个属性或者字段

二、mysql的基本命令

1、进入mysql

mysql  

 -p 指定密码

 -u 指定用户

 -P 指定端口 

 -h 主机地址

 -S 指定套接字文件，套接字文件是一种特殊的文件类型，用于通信，它提供了受文件系统访问控制保护的进程间通信。套接字就是支持TCP/IP网络通信的基本操作单元，linux以文件的形式实现套接口，与套接口相应的文件属于sockfs特殊文件系统，创建一个套接口就是在sockfs中创建一个特殊文件，并建立起为实现套接口功能的相关数据结构。

[root@localhost ~]# mysql -uroot -p123 -hlocalhost -P3306 -S /var/lib/mysql/mysql.sock  #套接字文件默认存储位置
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 32
Server version: 5.7.43 MySQL Community Server (GPL)

Copyright (c) 2000, 2023, Oracle and/or its affiliates.

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> 

2、关于库的操作

（1）查看已有数据库

语法：show databases；

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema | #虚拟库，主要存储了系统中一些数据库对象信息，例如用户表信息，列信息，权限信息，字符信息
| mysql              | #授权库，主要存储系统用户的权限信息
| performance_schema | #主要存储数据库服务器的性能参数
| sys                | #主要存储数据库服务器的性能参数（把performance-schema的复杂度降低）
+--------------------+
4 rows in set (0.00 sec)

（2）创建数据库

语法：create database 数据库名 default charset "指定字符集"；

数据库名命名规则：

区别大小写

唯一性

不能使用关键字 create select等

不能单独使用数字

 案例：创建一个名为school的数据库

mysql> create database school default charset"utf8";  #utf8mb4 表情，颜文字 
Query OK, 1 row affected (0.00 sec)

（3）查看创建的库信息

语法：show create database 数据库名；

mysql> show create database school;
+----------+-----------------------------------------------------------------+
| Database | Create Database                                                 |
+----------+-----------------------------------------------------------------+
| school   | CREATE DATABASE `school` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------------------+
1 row in set (0.00 sec)

（4）查看当前所在库（路径）

语法：select database( )；

mysql> select database();
+------------+
| database() |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)

（5）切换库

 语法：use 库名；

mysql> use school;  #切换库
Database changed
mysql> select database(); #查看当前所在库
+------------+
| database() |
+------------+
| school     |
+------------+
1 row in set (0.00 sec)

（6）删除库

mysql> drop database school;  #删除school库
Query OK, 4 rows affected (0.01 sec)

mysql> show databases; #查看所有库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

3、关于表的操作：

表是数据库存储数据的基本单元，由若干个字段组成，主要用来存储数据记录

（1）创建表

create table 表名(
        字段名1  类型 [(宽度) 约束条件],
        字段名2  类型 [(宽度) 约束条件],
        字段名3  类型 [(宽度) 约束条件]
)[存储引擎 字符集];
==在同一张表中，字段名是不能相同
==宽度和约束条件可选
==字段名和类型是必须的

mysql> create table student(
    -> `id` int primary key auto_increment  comment"学生id",
    -> `age` int not null comment"学生年龄",
    -> `address` varchar(20) comment"学生地址",
    -> `phone`   int comment"联系方式");
Query OK, 0 rows affected (0.00 sec)

（2）查看表

  查看表结构

语法：desc 表名；

mysql> desc student;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int(11)     | NO   | PRI | NULL    | auto_increment |
| age     | int(11)     | NO   |     | NULL    |                |
| address | varchar(20) | YES  |     | NULL    |                |
| phone   | int(11)     | YES  |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

 查看数据的详细信息

语法：show table status like“表名” \G

mysql> show table status like"student" \G
*************************** 1. row ***************************
           Name: student
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 1
    Create_time: 2023-09-26 18:08:09
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

查看创建表时的信息 

 语法：show create table 表名

mysql> show create table student;
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                                                                                                                                                                                       |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '学生id',
  `age` int(11) NOT NULL COMMENT '学生年龄',
  `address` varchar(20) DEFAULT NULL COMMENT '学生地址',
  `phone` int(11) DEFAULT NULL COMMENT '联系方式',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8               |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

 查询表中指定字段的值

  语法： select 指定字段 from 表名；

mysql> select age from student; #查看student表中的age
+-----+
| age |
+-----+
|  18 |
|  20 |
|  88 |
+-----+
3 rows in set (0.00 sec)

mysql> select age,id from student; #查看student表中的age和id
+-----+----+
| age | id |
+-----+----+
|  18 |  1 |
|  20 |  2 |
|  88 |  6 |
+-----+----+
3 rows in set (0.00 sec)

 查询表中所有字段

  语法：select * from 表名；

mysql> select * from student; #查看student表中的所有信息
+----+-----+---------+------------+
| id | age | address | phone      |
+----+-----+---------+------------+
|  1 |  18 | 山西    | 1999999999 |
|  2 |  20 | NULL    | 1888888888 |
|  6 |  88 | NULL    |       NULL |
+----+-----+---------+------------+
3 rows in set (0.00 sec)

（3）添加新字段

alter 修改表名称 修改字段名称 修改字段数据类型 修改字段的修饰符

语法：alter table 表名 add 新字段；

mysql> alter table student add math int null comment"数学成绩";       #添加一个新字段
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0


mysql> alter table student add name varchar(10) null comment"姓名" after id;  #在id后添加一个新字段name
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int(11)     | NO   | PRI | NULL    | auto_increment |
| name    | varchar(10) | YES  |     | NULL    |                |
| age     | int(11)     | NO   |     | NULL    |                |
| address | varchar(20) | YES  |     | NULL    |                |
| phone   | int(11)     | YES  |     | NULL    |                |
| math    | int(11)     | YES  |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

mysql> alter table student add (chinese int null comment"语文成绩",history int null comment"历史成绩"); #同时添加两个新字段

（4）修改表名

语法： rename table 原表名 to 新表名；

            alter table 原表名 rename 新表名；

mysql> rename table student to students;  #将表名student改为students
Query OK, 0 rows affected (0.01 sec)

mysql> show tables; #查看表
+------------------+
| Tables_in_school |
+------------------+
| students         |
+------------------+
1 row in set (0.00 sec)

mysql> alter table students rename student; #将students改为student
Query OK, 0 rows affected (0.01 sec)

mysql> show tables; #查看表
+------------------+
| Tables_in_school |
+------------------+
| student          |
+------------------+
1 row in set (0.00 sec)

（5）修改字段的的名称，数据类型，修饰符

语法： alter table 表名change 旧字段名 新字段名 字段类型 约束符

mysql> alter table student change math  english  int(12) null; #将math改名为English
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int(11)     | NO   | PRI | NULL    | auto_increment |
| name    | varchar(10) | YES  |     | NULL    |                |
| age     | int(11)     | NO   |     | NULL    |                |
| address | varchar(20) | YES  |     | NULL    |                |
| phone   | int(11)     | YES  |     | NULL    |                |
| english | int(12)     | YES  |     | NULL    |                |
| chinese | int(11)     | YES  |     | NULL    |                |
| history | int(11)     | YES  |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+

   不修改字段的名称，只修改修饰符

语法： alter table 表名 modify 字段名  字段类型 约束符

mysql> alter table student modify chinese int(13);
# 修改chinese是字段类型

（6）insert 插入数据（字符串必须用引号引起来）

语法： insert into 表名（字段）values（值）

mysql> insert into student values(1,18,"山西",1999999999);
Query OK, 1 row affected (0.00 sec)


mysql> insert into student(age,phone) values(20,1888888888);
Query OK, 1 row affected (0.01 sec)

mysql> insert into student set  id=6,age=88;
Query OK, 1 row affected (0.00 sec)


mysql> select * from student;
+----+-----+---------+------------+
| id | age | address | phone      |
+----+-----+---------+------------+
|  1 |  18 | 山西    | 1999999999 |
|  2 |  20 | NULL    | 1888888888 |
|  6 |  88 | NULL    |       NULL |
+----+-----+---------+------------+
3 rows in set (0.00 sec)

（7）delete删除数据

语法： delete from 表名 where id="  ";

mysql> delete from student where id=1; #删除id=1的字段
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+------+-----+---------+------------+---------+---------+---------+
| id | name | age | address | phone      | english | chinese | history |
+----+------+-----+---------+------------+---------+---------+---------+
|  2 | NULL |  20 | NULL    | 1888888888 |    NULL |    NULL |    NULL |
|  6 | NULL |  88 | NULL    |       NULL |    NULL |    NULL |    NULL |
+----+------+-----+---------+------------+---------+---------+---------+
2 rows in set (0.00 sec

（8）update 更新数据

语法：update 表名 set  要更新的信息  where id=" ";

mysql> select * from student;
+----+------+-----+---------+------------+---------+---------+---------+
| id | name | age | address | phone      | english | chinese | history |
+----+------+-----+---------+------------+---------+---------+---------+
|  2 | NULL |  20 | NULL    | 1888888888 |    NULL |    NULL |    NULL |
|  6 | NULL |  88 | NULL    |       NULL |    NULL |    NULL |    NULL |
+----+------+-----+---------+------------+---------+---------+---------+
2 rows in set (0.00 sec)

mysql> update student set name='xiaoming' where id=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student;
+----+----------+-----+---------+------------+---------+---------+---------+
| id | name     | age | address | phone      | english | chinese | history |
+----+----------+-----+---------+------------+---------+---------+---------+
|  2 | xiaoming |  20 | NULL    | 1888888888 |    NULL |    NULL |    NULL |
|  6 | NULL     |  88 | NULL    |       NULL |    NULL |    NULL |    NULL |
+----+----------+-----+---------+------------+---------+---------+---------+
2 rows in set (0.00 sec)

（9）复制表

   复制一张表

mysql> create table stu3(select * from student);
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from stu3;
+----+----------+-----+---------+------------+---------+---------+---------+
| id | name     | age | address | phone      | english | chinese | history |
+----+----------+-----+---------+------------+---------+---------+---------+
|  2 | xiaoming |  20 | NULL    | 1888888888 |    NULL |    NULL |    NULL |
|  6 | NULL     |  88 | NULL    |       NULL |    NULL |    NULL |    NULL |
+----+----------+-----+---------+------------+---------+---------+---------+
2 rows in set (0.00 sec)

mysql> create table stu4 (select id,name from student);
Query OK, 2 rows affected (0.02 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from stu4;
+----+----------+
| id | name     |
+----+----------+
|  2 | xiaoming |
|  6 | NULL     |
+----+----------+
2 rows in set (0.00 sec)

 复制表结构

mysql> create table stu5(SELECT  id,name,age,address,phone  from student where 5=4);
#等式不成立只复制结构，等式成立全部复制
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc stu5;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(11)     | NO   |     | 0       |       |
| name    | varchar(10) | YES  |     | NULL    |       |
| age     | int(11)     | NO   |     | NULL    |       |
| address | varchar(20) | YES  |     | NULL    |       |
| phone   | int(11)     | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> select * from stu5;
Empty set (0.00 sec)

（10）删除表

语法：drop table 表名；

mysql> drop table stu5;
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;
+------------------+
| Tables_in_school |
+------------------+
| stu3             |
| stu4             |
| student          |
+------------------+
3 rows in set (0.00 sec)

扩展：引擎

（1）查看支持的存储

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

（2）查看当前默认的存储引擎

mysql> show variables like "%storage_engine%";
+----------------------------------+--------+
| Variable_name                    | Value  |
+----------------------------------+--------+
| default_storage_engine           | InnoDB |
| default_tmp_storage_engine       | InnoDB |
| disabled_storage_engines         |        |
| internal_tmp_disk_storage_engine | InnoDB |
+----------------------------------+--------+
4 rows in set (0.01 sec)

（3）查看MySQL服务器的版本

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.43    |
+-----------+
1 row in set (0.00 sec)