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mysql -- 基本操作

孟祥忠诗歌 2022-04-04 阅读 42
mysql

数据库操作

1） 查看已有数据库：show databases;

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| myemployees        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql>

2) 创建库(指定字符集)：create datatabase 库名 [character set utf8];

mysql> create database test1 character set utf8;
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> create database test2 charset=utf8;
Query OK, 1 row affected, 1 warning (0.01 sec)

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

mysql>

3)  查看创建库的语句(字符集)：show create database 库名；

mysql> show create database test1;
+----------+---------------------------------------------------------------------------------------------------+
| Database | Create Database                                                                                   |
+----------+---------------------------------------------------------------------------------------------------+
| test1    | CREATE DATABASE `test1` /*!40100 DEFAULT CHARACTER SET utf8 */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+---------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

4) 查看当前所在数据库：select database();

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

5) 切换数据库：use 库名;

mysql> use test1;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| test1      |
+------------+
1 row in set (0.00 sec)

mysql>

6） 删除数据库：drop database 库名;

mysql> drop database test2;
Query OK, 0 rows affected (0.01 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| myemployees        |
| mysql              |
| performance_schema |
| sys                |
| test1              |
+--------------------+
6 rows in set (0.00 sec)

mysql>

7) 数据库命名规则

  • 数字、字母、下划线，单不能使用纯数字
  • 库名区分字母大小写
  • 不能使用特殊字符和mysql关键字

数据类型：

1） 数值类型：

整形：

  • tinyint：一个字节
  • smallint：2个字节
  • mediumint：3个字节
  • int/integer：4个字节
  • bigint：8个字节

浮点型：

  • float: 4个字节
  • double：8个字节

定点类型(精确值)：

  • decimal：用法decimal(M,D) M最多位数，D小数点位数

比特值类型：

  • bit

2）字符串类型

  • char和varchar类型
  • binary和varbinary类型
  • blob和text类型
  • enum类型和set类型

表的基本操作

1） 创建表

create table 表名（

字段名1 数据类型，

字段名2 数据类型，

...

字段名n 数据类型，

）；

  • 如果设置数值为无符号，则加上unsigned；
  • 如果不想字段为NULL，可以设置字段的属性为NOT NULL，在操作数据表时如果该字段的数据为NULL，就会报错；
  • DEFAULT表示设置一个字段的默认值;
  • AUTO_INCREMENT定义列为自增的属性，一般用于主键，数值会自动加1
  • PRIMARY KEY关键字用于定义列为主键。主键的值不能重复以及不能为空。
mysql> create table class (
    -> id int primary key auto_increment,
    -> name varchar(30) not null,
    -> age tinyint unsigned not null,
    -> gender enum('M','F'),
    -> score float default 0.0);
Query OK, 0 rows affected (0.05 sec)

mysql> create table interests (
    -> id int primary key auto_increment,
    -> name varchar(30) not null,
    -> hobby set('sing','dance','draw'),
    -> price decimal(8,2),
    -> level char not null,
    -> comment text);
Query OK, 0 rows affected (0.04 sec)

2） 查看数据表

show tables;

mysql> show tables;    /* 查看当前数据库中的数据表 */
+-----------------+
| Tables_in_test1 |
+-----------------+
| class           |
| interests       |
+-----------------+
2 rows in set (0.00 sec)

mysql>

3) 查看已有表的创建语句

show create table 表名；

mysql> show create table class;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                  |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| class | CREATE TABLE `class` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(30) NOT NULL,
  `age` tinyint unsigned NOT NULL,
  `gender` enum('M','F') DEFAULT NULL,
  `score` float DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

4） 查看表结构

desc 表名

mysql> desc class;
+--------+------------------+------+-----+---------+----------------+
| Field  | Type             | Null | Key | Default | Extra          |
+--------+------------------+------+-----+---------+----------------+
| id     | int              | NO   | PRI | NULL    | auto_increment |
| name   | varchar(30)      | NO   |     | NULL    |                |
| age    | tinyint unsigned | NO   |     | NULL    |                |
| gender | enum('M','F')    | YES  |     | NULL    |                |
| score  | float            | YES  |     | 0       |                |
+--------+------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

5） 删除表

drop table 表名；

mysql> create table test_table(
    -> id int,
    -> name varchar(30)
    -> );
Query OK, 0 rows affected (0.04 sec)

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| class           |
| interests       |
| test_table      |
+-----------------+
3 rows in set (0.00 sec)

mysql> drop table test_table;
Query OK, 0 rows affected (0.03 sec)

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| class           |
| interests       |
+-----------------+
2 rows in set (0.00 sec)

数据基本操作

1) 插入(insert)

  • insert into 表名 values(值1，值2，...);
  • insert into 表名 (字段1，...) values (值1，...);
mysql> insert into class values(1,'Zhangsan',20,'M',88); /* 按字段定义顺序赋值 */
Query OK, 1 row affected (0.01 sec)
mysql> insert into class (id,name,age,gender,score) values(2,'lisi',18,'F',90);/* 按字段给出的顺序赋值 */
Query OK, 1 row affected (0.00 sec)
mysql> insert into class values  /* 一次插入多条记录 */
    -> (3,'Wangwu',17,'F',91),
    -> (4,'zhaoliu','16','M',82);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

2) 查询(select)

  • select * from 表名 [where 条件];
  • select 字段1， 字段名2 ... from 表名 [where 条件];
mysql> select * from class;
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  20 | M      |    88 |
|  2 | lisi     |  18 | F      |    90 |
|  3 | Wangwu   |  17 | F      |    91 |
|  4 | zhaoliu  |  16 | M      |    82 |
+----+----------+-----+--------+-------+
4 rows in set (0.00 sec)

mysql> select name,age from class;
+----------+-----+
| name     | age |
+----------+-----+
| Zhangsan |  20 |
| lisi     |  18 |
| Wangwu   |  17 |
| zhaoliu  |  16 |
+----------+-----+
4 rows in set (0.00 sec)

where子句

where子句主要通过一定运算条件进行数据的筛选。MySQL主要有以下几种运算：

  • 算术运算符
  • 比较运算符
  • 逻辑运算符
  • 位运算符

算术运算符

  1. +：加
  2. -：减
  3. *：乘
  4. /或DIV：除
  5. %或MOD：取余
mysql> select name,age from class where age % 2 = 1;
+--------+-----+
| name   | age |
+--------+-----+
| Wangwu |  17 |
+--------+-----+
1 row in set (0.00 sec)
mysql> select name,age from class where age - 2 >= 18;
+----------+-----+
| name     | age |
+----------+-----+
| Zhangsan |  20 |
+----------+-----+
1 row in set (0.00 sec)

比较运算符

  • =：等于
  • <>或!=：不等于
  • >：大于
  • <：小于
  • <=：小于等于
  • >=：大于等于
  • BETWEEN ... AND ...：在这个范围内
  • NOT BETWEEN ... AND ...：不在这个范围内
  • IN：在这个集合中
  • NOT IN：不在这个集合内
  • <=>：严格比较两个NULL值是否相同
  • LIKE：模糊匹配
  • REGEXP或RLIKE：正则匹配
  • IS NULL：为空
  • IS NOT NULL：不为空
mysql> select * from class where  score>90;
+----+--------+-----+--------+-------+
| id | name   | age | gender | score |
+----+--------+-----+--------+-------+
|  3 | Wangwu |  17 | F      |    91 |
+----+--------+-----+--------+-------+
1 row in set (0.00 sec)

mysql> select * from class where age between 18 and 20;
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  20 | M      |    88 |
|  2 | lisi     |  18 | F      |    90 |
+----+----------+-----+--------+-------+
2 rows in set (0.00 sec)
mysql> select * from class where age in (16,20);
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  20 | M      |    88 |
|  4 | zhaoliu  |  16 | M      |    82 |
+----+----------+-----+--------+-------+
2 rows in set (0.00 sec)

逻辑运算符

  • NOT或!：非
  • AND：与
  • OR：或
  • XOR：与或
mysql> select * from class where age>16 and gender='M';
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  20 | M      |    88 |
+----+----------+-----+--------+-------+
1 row in set (0.00 sec)
mysql> select * from class where not score > 90;
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  20 | M      |    88 |
|  2 | lisi     |  18 | F      |    90 |
|  4 | zhaoliu  |  16 | M      |    82 |
+----+----------+-----+--------+-------+
3 rows in set (0.00 sec)

位运算符

  • &：按位与
  • |：按位或
  • ^：按位异或
  • !：取反
  • <<：左移
  • >>：右移

更新表记录(update)

update 表名 set 字段1=值1，字段2=值2，... where 条件；

mysql> update class set age=14,score=70 where name='Zhangsan';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from class where name='Zhangsan';
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  14 | M      |    70 |
+----+----------+-----+--------+-------+
1 row in set (0.00 sec)

删除表记录(delete)

delete from 表名 where 条件;

mysql> delete from class where name='lisi';
Query OK, 1 row affected (0.00 sec)
mysql> select * from class;
+----+----------+-----+--------+-------+
| id | name     | age | gender | score |
+----+----------+-----+--------+-------+
|  1 | Zhangsan |  14 | M      |    70 |
|  3 | Wangwu   |  17 | F      |    91 |
|  4 | zhaoliu  |  16 | M      |    82 |
+----+----------+-----+--------+-------+
3 rows in set (0.00 sec)

表字段的操作(alter)

语法：alter table 表名 执行动作；

1） 添加字段(add)

  • alter table 表名 add 字段名 数据类型；
  • alter table 表名 add 字段名 数据类型 first；
  • alter table 表名 add 字段名 数据类型 after 字段名；
mysql> create table test(
    -> name varchar(30));
Query OK, 0 rows affected (0.05 sec)

mysql> alter table test add sex enum('M','F');
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table test add id int primary key auto_increment first;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table test add age tinyint after name;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc test;
+-------+---------------+------+-----+---------+----------------+
| Field | Type          | Null | Key | Default | Extra          |
+-------+---------------+------+-----+---------+----------------+
| id    | int           | NO   | PRI | NULL    | auto_increment |
| name  | varchar(30)   | YES  |     | NULL    |                |
| age   | tinyint       | YES  |     | NULL    |                |
| sex   | enum('M','F') | YES  |     | NULL    |                |
+-------+---------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)

mysql>

2） 删除字段(drop)

  • alter table 表名 drop 字段名 ；
mysql> alter table test drop sex;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc test;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int         | NO   | PRI | NULL    | auto_increment |
| name  | varchar(30) | YES  |     | NULL    |                |
| age   | tinyint     | YES  |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

3） 修改数据类型(modify)

  • alter table 表名 modify 字段名 新数据类型；
mysql> alter table test modify age int unsigned;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc test;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int          | NO   | PRI | NULL    | auto_increment |
| name  | varchar(30)  | YES  |     | NULL    |                |
| age   | int unsigned | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

4) 表重命名(rename)

  • alter table 表名 rename 新表名；
mysql> alter table test rename student;
Query OK, 0 rows affected (0.03 sec)

日期时间函数

  • now()：返回服务器当前时间。
  • curdate()：返回当前日期。
  • curtime()：返回当前时间。
  • date(date)：返回指定时间的日期。
  • time(date)：返回指定时间的时间。
mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2022-03-30 20:11:58 |
+---------------------+
1 row in set (0.00 sec)

mysql> select curdate();
+------------+
| curdate()  |
+------------+
| 2022-03-30 |
+------------+
1 row in set (0.00 sec)

mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 20:12:17  |
+-----------+
1 row in set (0.00 sec)

mysql> select date('2022-03-30 20:11:58');
+-----------------------------+
| date('2022-03-30 20:11:58') |
+-----------------------------+
| 2022-03-30                  |
+-----------------------------+
1 row in set (0.00 sec)

mysql> select time('2022-03-30 20:11:58');
+-----------------------------+
| time('2022-03-30 20:11:58') |
+-----------------------------+
| 20:11:58                    |
+-----------------------------+
1 row in set (0.00 sec)

时间和日期类型

  • DATE，DATETIME和TIMESTAMP类型
  • TIME类型
  • 年份类型YEAR
类型

大小

（字节）

范围格式用途
DATE3

1000-01-01/

9999-12-31

YYYY-MM-DD日期值
TIME3

-838:59:59/

838:59:59

HH:MM:SS时间值或持续时间
YEAR11901/2155YYYY年份
DATETIME8

1000-01-01 00:00:00/

9999-12-31 23:59:59

YYYY-MM-DD HH:MM:SS混合日期和时间值
TIMESTAMP4

1970-01-01 00:00:00/2038

结束时间是第2147483647秒

YYYYMMDD HHMMSSS混合日期和时间值，时间戳

时间格式

  • date："YYYY-MM-DD"
  • time："HH:MM:SS"
  • datetime："YYYY-MM-DD HH:MM:SS"
  • timestamp："YYYY-MM-DD HH:MM:SS"

注意：

  1. datetime：不给值 ，默认返回NULL。
  2. timestamp：不给值，默认返回系统当前时间。
mysql> alter table class add entry_year date;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from class;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | NULL       |
|  3 | Wangwu   |  17 | F      |    91 | NULL       |
|  4 | zhaoliu  |  16 | M      |    82 | NULL       |
+----+----------+-----+--------+-------+------------+
3 rows in set (0.00 sec)

mysql> update class set entry_year='2022-03-30' where id=1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from class;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  3 | Wangwu   |  17 | F      |    91 | NULL       |
|  4 | zhaoliu  |  16 | M      |    82 | NULL       |
+----+----------+-----+--------+-------+------------+
3 rows in set (0.00 sec)

日期时间运算

  1. 语法格式：select * from 表名 where 字段名 =(时间  运算符 interval 时间间隔单位)
  2. 时间间隔单位：1 day | 1 hour | 2 minute | 2 year | 3 month
mysql> update class set entry_year=curdate()-interval 2 month  where entry_year is null;
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> select * from class;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  3 | Wangwu   |  17 | F      |    91 | 2022-01-30 |
|  4 | zhaoliu  |  16 | M      |    82 | 2022-01-30 |
+----+----------+-----+--------+-------+------------+
3 rows in set (0.00 sec)



模糊查询和正则查询

模糊查询

1) LIKE用于在where子句进行模糊查询，SQL LIKE子句中使用百分号%来表示任何0个或多个字符，下划线_表示一个字符。

使用LIKE子句从数据表中读取数据的通用语法：

select field1, field2, ... fieldN from table_name where fieldx  like condition1;

mysql> select * from class where name like 'Z%';
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  4 | zhaoliu  |  16 | M      |    82 | 2022-01-30 |
+----+----------+-----+--------+-------+------------+
2 rows in set (0.00 sec)

2) mysql中对正则表达式的支持有限，只支持部分正则元字符

select field1, field2, ..., fieldN from table_name where fieldx REGEXP condition1;

排序

order by子句来设定按哪个字段哪种方式来进行排序，再返回搜索结果。使用order by子句将查询数据排序后再返回数据：

select field1, field2, ..., fieldN from table_name where field1 order by field1 [ASC [DESC]]

默认情况ASC表示升序，DESC表示降序。

mysql> select * from class order by age;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  4 | zhaoliu  |  16 | M      |    82 | 2022-01-30 |
|  3 | Wangwu   |  17 | F      |    91 | 2022-01-30 |
+----+----------+-----+--------+-------+------------+
3 rows in set (0.00 sec)

分页

limit子句用于限制由select语句返回的数据数量或者UPDATE，DELETE语句的操作数量。

带有limit子句的select语句的基本语法如下：

select column1, column2, ... ,columnN

from table_name

where filed

limit [num]

mysql> select * from class limit 1;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
+----+----------+-----+--------+-------+------------+
1 row in set (0.00 sec)

联合查询

union操作用于连接两个以上的SELECT语句的结果组合到一个结果集合中。多个select语句会删除重复的数据。

union操作符语法格式：

select expression1, expression2, ...,  expressionN

from tables

[where condtions]

union [ALL | DISTINCT]

select expression1, expression2, ...,  expressionN

from tables

[where condtions]

mysql> select * from class where id=1
    -> union
    -> select * from class where id=3;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  3 | Wangwu   |  17 | F      |    91 | 2022-01-30 |
+----+----------+-----+--------+-------+------------+
2 rows in set (0.00 sec)

数据库备份

1） 备份命令格式：mysqldump -u用户名 -p 源库名 > 路径/备份名.sql

  • --all databases：      备份所有库
  • 库名：                     备份单个库
  • -B 库1 库2 库3 ：    备份多个库
  • 库名 表1 表2 表3 ：备份指定库的多个表
[root@bjAli mysql]# ls
[root@bjAli mysql]# mysqldump -uroot -p test1 > test1.sql
Enter password:
[root@bjAli mysql]# ls
test1.sql
[root@bjAli mysql]#

2） 恢复命令格式：mysql -u用户名 -p 目标库名 < ***.sql

  • --one-database：从所有库备份中恢复一个库
mysql> drop database test1;
Query OK, 3 rows affected (0.06 sec)
mysql> create database student;
Query OK, 1 row affected (0.01 sec)

mysql> quit
Bye
[root@bjAli mysql]# mysql -uroot -p student < test1.sql
Enter password:
[root@bjAli mysql]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 89
Server version: 8.0.28 MySQL Community Server - GPL

Copyright (c) 2000, 2022, 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> use student;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| class             |
| interests         |
| student           |
+-------------------+
3 rows in set (0.01 sec)

mysql> select * from class;
+----+----------+-----+--------+-------+------------+
| id | name     | age | gender | score | entry_year |
+----+----------+-----+--------+-------+------------+
|  1 | Zhangsan |  14 | M      |    70 | 2022-03-30 |
|  3 | Wangwu   |  17 | F      |    91 | 2022-01-30 |
|  4 | zhaoliu  |  16 | M      |    82 | 2022-01-30 |
+----+----------+-----+--------+-------+------------+
3 rows in set (0.00 sec)
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