【MySQL】MySQL数据库的基本操作一

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2022-02-19


一. 数据库操作

1. 查看数据库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| zmedu              |
+--------------------+
5 rows in set

注意：


  • MySQL数据库指令不区分大小写，操作真正的表和库的时候才区分大小写
  • 任何命令都以；结束

2. 创建数据库
mysql> create database zmgaosh;
Query OK, 1 row affected

每创建一个数据库都会在data下创建同名的文件夹，一个数据库说到底就是个文件夹

【MySQL】MySQL数据库的基本操作一_数据库

查看数据库，发现zmgaosh已经创建好了；

【MySQL】MySQL数据库的基本操作一_数据库_02

3. 选择数据库

select database(); 查看当前在哪个库

use zmgaosh ; 切换到zmgaosh

mysql> select database();
+------------+
| database() |
+------------+
| zmedu      |
+------------+
1 row in set

mysql> use zmgaosh;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| zmgaosh    |
+------------+
1 row in set

mysql>
4. 删除数据库

drop 删除数据库命令

mysql> drop database zmgaosh;
Query OK, 0 rows affected

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| zmedu              |
+--------------------+
5 rows in set

mysql>

注意： drop命令将删除指定数据库的所有的表，而且没有任何提示；如果你到data目录下查看，会发现没有zmgaosh这个文件夹了。

二. 数据库表的操作

1. 查看表
mysql> use zmedu;
Database changed
mysql> show tables;
+-----------------+
| Tables_in_zmedu |
+-----------------+
| t               |
+-----------------+
1 row in set

mysql>

zmedu数据库里我创建了一个t表，所以使用show就可以看到，zmedu库中只有一个表t。

2. 创建表

语法：create table 表名 (字段名 类型, 字段名 类型, 字段名 类型);

mysql> create table hero(id int(20),name char(40),level int(2));
Query OK, 0 rows affected

mysql> show tables;
+-----------------+
| Tables_in_zmedu |
+-----------------+
| hero            |
| t               |
+-----------------+
2 rows in set
3. 查看表结构的表述
mysql> desc hero;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int      | YES  |     | NULL    |       |
| name  | char(40) | YES  |     | NULL    |       |
| level | int      | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set

可以看到有三个字段，id，name 和level，他们的类型

​如果想查看创建表时候所执行的命令：​

mysql> show create table hero;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                               |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
| hero  | CREATE TABLE `hero` (
  `id` int DEFAULT NULL,
  `name` char(40) DEFAULT NULL,
  `level` int DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql>

在MySQL8里，创建表的默认 编码是UTF8

4. 删除表
mysql> create table hero1(id int(20),name char(40),level int(2));
Query OK, 0 rows affected

mysql> show tables;
+-----------------+
| Tables_in_zmedu |
+-----------------+
| hero            |
| hero1           |
| t               |
+-----------------+
3 rows in set

mysql> drop table hero1;
Query OK, 0 rows affected

mysql> show tables;
+-----------------+
| Tables_in_zmedu |
+-----------------+
| hero            |
| t               |
+-----------------+
2 rows in set
5. 插入记录

使用insert into插入数据， insert into …values

mysql> insert into hero values(1,'zmgaosh',20);
Query OK, 1 row affected

mysql> insert into hero(id,name) values(2,'gaosh
');
Query OK, 1 row affected
6. 查看表记录
mysql> select * from hero;
+----+---------+-------+
| id | name    | level |
+----+---------+-------+
|  1 | zmgaosh |    20 |
|  2 | gaosh   | NULL  |
+----+---------+-------+
2 rows in set

只查某一个字段

mysql> select id from hero;
+----+
| id |
+----+
|  1 |
|  2 |
+----+
2 rows in set

mysql>

字段的操作

1. 修改字段类型

查看一下原来的字段结构

mysql> desc hero;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int      | YES  |     | NULL    |       |
| name  | char(40) | YES  |     | NULL    |       |
| level | int      | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
3 rows in set

可以看到有id，name ，level 类型

​我们现在把name的char类型改为varchar;​

mysql> alter table hero modify name varchar(4
0);
Query OK, 2 rows affected
Records: 2  Duplicates: 0  Warnings: 0

mysql> desc hero;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int         | YES  |     | NULL    |       |
| name  | varchar(40) | YES  |     | NULL    |       |
| level | int         | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set
2. 修改字段名称和类型

语法： alter table 表名 change 原字段名 新字段名 新字段类型

mysql> alter table hero change name heroname char(40);
Query OK, 2 rows affected
Records: 2  Duplicates: 0  Warnings: 0

mysql> desc hero;
+----------+----------+------+-----+---------+-------+
| Field    | Type     | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| id       | int      | YES  |     | NULL    |       |
| heroname | char(40) | YES  |     | NULL    |       |
| level    | int      | YES  |     | NULL    |       |
+----------+----------+------+-----+---------+-------+
3 rows in set
3. 添加字段

语法： alter table 表名 add 字段 类型

mysql> alter table hero add team enum('A','B
');
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc hero;
+----------+---------------+------+-----+---------+-------+
| Field    | Type          | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| id       | int           | YES  |     | NULL    |       |
| heroname | char(40)      | YES  |     | NULL    |       |
| level    | int           | YES  |     | NULL    |       |
| team     | enum('A','B') | YES  |     | NULL    |       |
+----------+---------------+------+-----+---------+-------+
4 rows in set

mysql>
4. 删除字段

语法：alter table 表名 drop 字段名 ;

mysql> desc hero;
+----------+---------------+------+-----+---------+-------+
| Field    | Type          | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| id       | int           | YES  |     | NULL    |       |
| heroname | char(40)      | YES  |     | NULL    |       |
| level    | int           | YES  |     | NULL    |       |
| team     | enum('A','B') | YES  |     | NULL    |       |
+----------+---------------+------+-----+---------+-------+
4 rows in set

mysql> alter table hero drop team;
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc hero;
+----------+----------+------+-----+---------+-------+
| Field    | Type     | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| id       | int      | YES  |     | NULL    |       |
| heroname | char(40) | YES  |     | NULL    |       |
| level    | int      | YES  |     | NULL    |       |
+----------+----------+------+-----+---------+-------+
3 rows in set
5. 删除行

删除id=2的行

mysql> select * from hero;
+----+----------+-------+
| id | heroname | level |
+----+----------+-------+
|  1 | zmgaosh  |    20 |
|  2 | gaosh    | NULL  |
+----+----------+-------+
2 rows in set

mysql> delete from hero where id=2;
Query OK, 1 row affected

mysql> select * from hero;
+----+----------+-------+
| id | heroname | level |
+----+----------+-------+
|  1 | zmgaosh  |    20 |
+----+----------+-------+
1 row in set
6. 更新

更新id1 变成22

mysql> select * from hero;
+----+----------+-------+
| id | heroname | level |
+----+----------+-------+
|  1 | zmgaosh  |    20 |
+----+----------+-------+
1 row in set

mysql> update hero set id=22;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from hero;
+----+----------+-------+
| id | heroname | level |
+----+----------+-------+
| 22 | zmgaosh  |    20 |
+----+----------+-------+
1 row in set

总结

数据库和数据库表的增删改查是一个运维必会的，如果连这都不会，就放弃运维了。



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