说明
用命令行能增强初学者编写SQL的准确度和熟练度，一旦发现输错了，确保命令是错的，输入英文分号，直接会命令报错从而重新输入。
登录
输入用户名和密码即可登录（免密除外）
mysql -u (your username such as 'root') -p
Enter password: ***************(your password)
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.16 MySQL Community Server - GPL
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affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
查所有的库
查所有的数据库。
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jindu |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
6 rows in set (0.75 sec)
删库
由于我们需要重新使用test这个数据库，而里面确实乏善可陈，所以删了重建。
mysql> drop database test;
Query OK, 0 rows affected (0.21 sec)
接下来重新查库，发现少了test库。
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jindu |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
建库
删库是为了重建，那就建一下：
mysql> create database test;
Query OK, 1 row affected (0.17 sec)
再查库，发现test库出现了。
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jindu |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
6 rows in set (0.00 sec)
进入test数据库
mysql使用use命令可以进入指定数据库。
mysql> use test;
Database changed
接下来的操作就在test库中展开啦！
查库中所有的表
新库显然无表，查到空集。
mysql> show tables;
Empty set (0.00 sec)
库中建表
没有表，就建立一个表呗，使用create可以建表，名为stu_info，因为接下来的数据是学生信息。
mysql> create table stu_info
-> (id int primary key not null,
-> name varchar(10) not null,
-> age int not null,
-> email varchar(20),
-> country varchar(10),
-> gpa float(4) not null);
Query OK, 0 rows affected (0.93 sec)
再查表，发现有了stu_info这张表。
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| stu_info |
+----------------+
1 row in set (0.41 sec)
全表查询
select * 虽说在高级应用中是低效的，但对于初学者也是必须掌握的，可查全表信息并返回。
由于我们刚建的表是空表，所以返回空集。
mysql> select * from stu_info;
Empty set (0.36 sec)
表中插入一行
在表中插入一行信息（一个元组）
mysql> insert into stu_info
-> values('1', 'XiaoMing', '19', '[email protected]', 'China', '3.5945');
Query OK, 1 row affected (0.41 sec)
我们查一下全表：
mysql> select * from stu_info;
+----+----------+-----+------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+------------------+---------+--------+
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
+----+----------+-----+------------------+---------+--------+
1 row in set (0.00 sec)
确实有一行数据了。
接下来再插入四行：
mysql> insert into stu_info
-> values('2', 'Bob', '20', '[email protected]', 'USA', '3.9047');
Query OK, 1 row affected (0.41 sec)
mysql> insert into stu_info
-> values('3', 'Steven', '21', '[email protected]', 'UK', '2.5633');
Query OK, 1 row affected (0.41 sec)
mysql> insert into stu_info
-> values('4', 'LiHua', '20', '[email protected]', 'China', '4.9999');
Query OK, 1 row affected (0.44 sec)
mysql> insert into stu_info
-> values('5', 'Amy', '19', '[email protected]', 'China', '4.1000');
Query OK, 1 row affected (0.40 sec)
我们查一下全表：
mysql> select * from stu_info;
+----+----------+-----+---------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+---------------------+---------+--------+
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
| 2 | Bob | 20 | bobbob@gmail.com | USA | 3.9047 |
| 3 | Steven | 21 | steven521@gmail.com | UK | 2.5633 |
| 4 | LiHua | 20 | lihua@thu.stu.com | China | 4.9999 |
| 5 | Amy | 19 | 20205205@163.com | China | 4.1 |
+----+----------+-----+---------------------+---------+--------+
5 rows in set (0.00 sec)
OK，五行信息插入完了。
更改表中一条记录的信息
使用update可以改表中的记录：
mysql> update stu_info
-> set gpa='1.8888'
-> where name='Steven';
Query OK, 1 row affected (0.44 sec)
Rows matched: 1 Changed: 1 Warnings: 0
我们查一下全表：
mysql> select * from stu_info;
+----+----------+-----+---------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+---------------------+---------+--------+
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
| 2 | Bob | 20 | bobbob@gmail.com | USA | 3.9047 |
| 3 | Steven | 21 | steven521@gmail.com | UK | 1.8888 |
| 4 | LiHua | 20 | lihua@thu.stu.com | China | 4.9999 |
| 5 | Amy | 19 | 20205205@163.com | China | 4.1 |
+----+----------+-----+---------------------+---------+--------+
5 rows in set (0.00 sec)
可怜的Steven啊，他的GPA降到1.8888了，太惨了orz
查询结果排序
使用 order by，查询结果排序可以是升序或者降序，默认是升序（升序是指从上到下依次增大，降序反是）：
mysql> select * from stu_info
-> order by gpa;
+----+----------+-----+---------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+---------------------+---------+--------+
| 3 | Steven | 21 | steven521@gmail.com | UK | 1.8888 |
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
| 2 | Bob | 20 | bobbob@gmail.com | USA | 3.9047 |
| 5 | Amy | 19 | 20205205@163.com | China | 4.1 |
| 4 | LiHua | 20 | lihua@thu.stu.com | China | 4.9999 |
+----+----------+-----+---------------------+---------+--------+
5 rows in set (0.00 sec)
加上desc，结果呈现降序：
mysql> select * from stu_info
-> order by gpa desc;
+----+----------+-----+---------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+---------------------+---------+--------+
| 4 | LiHua | 20 | lihua@thu.stu.com | China | 4.9999 |
| 5 | Amy | 19 | 20205205@163.com | China | 4.1 |
| 2 | Bob | 20 | bobbob@gmail.com | USA | 3.9047 |
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
| 3 | Steven | 21 | steven521@gmail.com | UK | 1.8888 |
+----+----------+-----+---------------------+---------+--------+
5 rows in set (0.00 sec)
查询结果只返回部分属性
把 select * 的 “*”换成指定的属性，可以有很多并用逗号分隔，这里还加了排序：
mysql> select id, name, gpa from stu_info
-> order by gpa desc;
+----+----------+--------+
| id | name | gpa |
+----+----------+--------+
| 4 | LiHua | 4.9999 |
| 5 | Amy | 4.1 |
| 2 | Bob | 3.9047 |
| 1 | XiaoMing | 3.5945 |
| 3 | Steven | 1.8888 |
+----+----------+--------+
5 rows in set (0.00 sec)
使用where查询符合指定条件的数据
mysql> select id, name, gpa from stu_info
-> where gpa>3.5
-> order by gpa desc;
+----+----------+--------+
| id | name | gpa |
+----+----------+--------+
| 4 | LiHua | 4.9999 |
| 5 | Amy | 4.1 |
| 2 | Bob | 3.9047 |
| 1 | XiaoMing | 3.5945 |
+----+----------+--------+
4 rows in set (0.00 sec)
where条件相当于编程语言中的boolean值，可使用and表示且、or表示或。
下面的条件是且，查询结果会少一些：
mysql> select id, name, gpa from stu_info
-> where gpa>3.5 and id>2
-> order by gpa desc;
+----+-------+--------+
| id | name | gpa |
+----+-------+--------+
| 4 | LiHua | 4.9999 |
| 5 | Amy | 4.1 |
+----+-------+--------+
2 rows in set (0.00 sec)
下面是或，查询结果会多一些：
mysql> select id, name, gpa from stu_info
-> where gpa>3.5 or id>2
-> order by gpa desc;
+----+----------+--------+
| id | name | gpa |
+----+----------+--------+
| 4 | LiHua | 4.9999 |
| 5 | Amy | 4.1 |
| 2 | Bob | 3.9047 |
| 1 | XiaoMing | 3.5945 |
| 3 | Steven | 1.8888 |
+----+----------+--------+
5 rows in set (0.00 sec)
查询结果去重
select后加上distinct，可以实现查询去重。
这里简单的选择了country一个属性，数据库所有的country属性只有China、USA、UK三种，China是有重复的，使用distinct可以做到查询结果去重：
mysql> select distinct country from stu_info;
+---------+
| country |
+---------+
| China |
| USA |
| UK |
+---------+
3 rows in set (0.00 sec)
从表中删除一行
delete可以删一行数据，这里指定的where条件是id=3（别忘了使用引号），可删除id=3的一行数据：
mysql> delete from stu_info
-> where id='3';
Query OK, 1 row affected (0.41 sec)
mysql> select * from stu_info;
+----+----------+-----+-------------------+---------+--------+
| id | name | age | email | country | gpa |
+----+----------+-----+-------------------+---------+--------+
| 1 | XiaoMing | 19 | 123456789@qq.com | China | 3.5945 |
| 2 | Bob | 20 | bobbob@gmail.com | USA | 3.9047 |
| 4 | LiHua | 20 | lihua@thu.stu.com | China | 4.9999 |
| 5 | Amy | 19 | 20205205@163.com | China | 4.1 |
+----+----------+-----+-------------------+---------+--------+
4 rows in set (0.00 sec)
清空数据表
如果不用where做限定，就会把整个表的数据全删了，但表的结构还保留。
因为表在建立之初就定好了结构，所以表还在，哪怕是空的，也还保留了结构。
delete * 是不合语法规范的，至少不合mysql的规范，既不能清表也不能删表：
mysql> delete * from stu_info;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '* from stu_info' at line 1
真想删就别加*：
mysql> delete from stu_info;
Query OK, 4 rows affected (0.43 sec)
删完了可以查全表，真的空了：
mysql> select * from stu_info;
Empty set (0.00 sec)
删表
看一眼库中所有的表，果然这个表只是空了，表本身还在：
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| stu_info |
+----------------+
1 row in set (0.00 sec)
接下来这个表没啥用了，删掉吧，反正只是一个实验罢了，drop才是正解：
mysql> drop table stu_info;
Query OK, 0 rows affected (0.53 sec)
重新查库中全表：
mysql> show tables;
Empty set (0.00 sec)
确实空了，表删没了。
再删库
查一下，六个库：
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jindu |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
6 rows in set (0.00 sec)
使用drop把test库删掉：
mysql> drop database test;
Query OK, 0 rows affected (0.41 sec)
再查查所有的库：
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| jindu |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
OK删掉了。
退出
退出有多种方式，反正\q是可以退出的啦：
mysql> \q
Bye
总结
本文带领读者使用命令行运行MySQL，执行了基础的SQL增删改查语句，还完成了登录退出、建库删库、建表删表的操作，还望能带领初学者快速入门SQL。
