From 25d516131ec84e3ff3f2aaf09220a4dfa8b65221 Mon Sep 17 00:00:00 2001 From: diandian Date: Mon, 29 Apr 2024 16:24:47 +0800 Subject: [PATCH] =?UTF-8?q?=E6=9B=B4=E6=96=B0=20'mysql-MD/=E7=AC=AC?= =?UTF-8?q?=E4=BA=8C=E7=AB=A0=EF=BC=9A=E6=95=B0=E6=8D=AE=E5=BA=93=E7=AE=A1?= =?UTF-8?q?=E7=90=86=E5=8F=8A=E6=95=B0=E6=8D=AE=E7=B1=BB=E5=9E=8B.md'?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...二章：数据库管理及数据类型.md | 1722 ++++++++--------- 1 file changed, 861 insertions(+), 861 deletions(-) diff --git a/mysql-MD/第二章：数据库管理及数据类型.md b/mysql-MD/第二章：数据库管理及数据类型.md index b51bb12..61bcb2e 100644 --- a/mysql-MD/第二章：数据库管理及数据类型.md +++ b/mysql-MD/第二章：数据库管理及数据类型.md @@ -1,861 +1,861 @@ -

数据库管理及数据类型

- -**作者：行癫（盗版必究）** - ------- - -## 一：数据类型 - -#### 1.数值类型 - -##### 整数类型 - -​ 整数类型：TINYINT SMALLINT MEDIUMINT INT BIGINT - -​ 作用：用于存储用户的年龄、游戏的Level、经验值等 - -![image-20220920124821420](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124821420.png) - -##### 浮点数类型 - -​ 浮点数类型：FLOAT DOUBLE - -​ 作用：用于存储用户的身高、体重、薪水等 - -![image-20220920124919373](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124919373.png) - -```shell -float(5,3) 5宽度 3精度 -注意： - 宽度不算小数点 - 宽度-精度=点前 -案例： -MySQL [(none)]> create database diandian; -Query OK, 1 row affected (0.00 sec) - -MySQL [(none)]> use diandian -Database changed -MySQL [diandian]> create table t1(id float(6,2)); -Query OK, 0 rows affected (0.24 sec) - -MySQL [diandian]> insert into t1 values('2.22'); -``` - -##### 定点数类型 - -​ 定点数类型：DEC - -​ 定点数在MySQL内部以字符串形式存储，比浮点数更精确，适合用来表示货币等精度高的数据 - -##### 位类型 - -​ 位类型：BIT - -​ BIT(M)可以用来存放多位二进制数，M范围从1~64，如果不写默认为1位 - -#### 2.字符串类型 - -​ CHAR系列 CHAR VARCHAR - -​ TEXT系列 TINYTEXT TEXT MEDIUMTEXT LONGTEXT - -​ BLOB 系列 TINYBLOB BLOB MEDIUMBLOB LONGBLOB - -​ BINARY系列 BINARY VARBINARY - -![image-20220920132114919](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132114919.png) - -##### 枚举类型 - -​ 枚举类型：枚举列可以把一些不重复的字符串存储成一个预定义的集合 - -```shell -mysql> create table enum_table( e ENUM('fish','apple','dog')); -Query OK, 0 rows affected (0.35 sec) -mysql> insert into enum_table(e) values('fish'); -Query OK, 1 row affected (0.11 sec) - -mysql> select * from enum_table; -+------+ -| e | -+------+ -| fish | -+------+ -1 row in set (0.00 sec) - -mysql> insert into enum_table(e) values('nihao'); -ERROR 1265 (01000): Data truncated for column 'e' at row 1 -``` - -##### 时间和日期类型 - -​ 时间和日期类型：DATE TIME DATETIME TIMESTAMP YEAR - -​ 作用：用于存储用户的注册时间，文章的发布时间，文章的更新时间，员工的入职时间等 - -![image-20220920132630856](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132630856.png) - -```shell -mysql> create table t8 ( - id1 timestamp NOT NULL default CURRENT_TIMESTAMP, - id2 datetime default NULL -); - - timestamp 类型的列还有个特性：默认情况下，在 insert, update 数据时，timestamp 列会自动以当前时间（CURRENT_TIMESTAMP）填充/更新。“自动”的意思就是，你不去管它，MySQL 会替你去处理。 - -mysql> insert into t8(id1) values('20180109000000'); -mysql> select * from t8; -+---------------------+------+ -| id1 | d2 | -+---------------------+------+ -| 2018-01-09 00:00:00 | NULL | -+---------------------+------+ -1 row in set (0.00 sec) - -扩展： -select now();查看当前时间 -``` - -## 二：表操作 - -#### 1.案例 - -表:：school.student1 - -``` -字段 字段 字段 -id name sex age -1 tom male 23 记录 -2 jack male 21 记录 -3 alice female 19 记录 -``` - -语法： - -```shell -create table 表名(自定义)( - 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 -``` - -创建库表： - -```shell -mysql> CREATE DATABASE school; //创建数据库school -mysql> use school; -mysql> create table student1( - id int, - name varchar(50), - sex enum('m','f'), - age int - ); -Query OK, 0 rows affected (0.03 sec) -``` - -查看库： - -```shell -mysql> show tables; -+------------------+ -| Tables_in_school | -+------------------+ -| student1 | -+------------------+ -1 row in set (0.00 sec) -``` - -插入语法： - -``` -insert into 表名(字段1,字段2...) values(字段值列表...); -``` - -插入数据： - -```shell -mysql> insert into student1(id,name,sex,age) values(1,'xingdia','m','26'); -``` - -查看表结构： - -```shell -mysql> desc student1; -+-------+---------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+---------------+------+-----+---------+-------+ -| id | int(11) | YES | | NULL | | -| name | varchar(50) | YES | | NULL | | -| sex | enum('m','f') | YES | | NULL | | -| age | int(11) | YES | | NULL | | -+-------+---------------+------+-----+---------+-------+ -4 rows in set (0.00 sec) -``` - -查询数据： - -```shell -mysql> select id,name,sex,age from student1; //查询表中所有字段的值 -Empty set (0.00 sec) - -mysql> select * from student1; /查询表中所有字段的值 -Empty set (0.00 sec) - -mysql> select name,age from student1; //查询表中指定字段的值 -Empty set (0.00 sec) -``` - -扩展插入： - -```shell -mysql> insert into student1 values (1,'xingdian','m',33),(2,'alice','m',20),(3,'jack','m',40); //顺序插入 -Query OK, 3 rows affected (0.14 sec) -Records: 3 Duplicates: 0 Warnings: 0 - -mysql> insert into student1(name,age) values ('zhuzhu',10),('gougou',20); //只向指定的字段插入值 -Query OK, 2 rows affected (0.12 sec) -Records: 2 Duplicates: 0 Warnings: 0 -``` - -#### 2.案例 - -表：school.student2 - -```shell - 字段名 数据类型 -编号 id int -姓名 name varchar(50) -出生年份 born_year year -生日 birthday date -上课时间 class_time time -注册时间 reg_time datetime -``` - -创建表： - -```shell -mysql> create table student2( - id int, - name varchar(50), - born_year year, - birthday date, - class_time time, - reg_time datetime - ); -``` - -插入数据： - -```shell -mysql> insert into student2 values(1,'tom',now(),now(),now(),now()); -mysql> insert into student2 values(2,'jack',1982,19821120,123000,20140415162545); -``` - -表：school.student3 - -```shell -id id int -姓名 name varchar(50) -性别 sex enum('male','female') -爱好 hobby set('music','book','game','disc') -``` - -创建表： - -```shell -mysql> create table student3( - id int, - name varchar(50), - sex enum('male','female'), - hobby set('music','book','game','disc') - ); -``` - -查看表结构： - -```shell -mysql> desc student3; -mysql> show create table student3\G -``` - -插入数据： - -```shell -mysql> insert into student3 values (1,'tom','male','book,game'); -mysql> insert into student3 values (2,'jack','male','film'); -``` - -注意： - -​ DESCRIBE查看表结构 - -```shell -DESCRIBE 表名; -DESC 表名; -``` - -​ 查看表详细结构 - -```shell -SHOW CREATE TABLE 表名; -``` - -## 三：表完整性约束 - -#### 1.作用 - -​ 用于保证数据的完整性和一致性 - -#### 2.约束条件 - -PRIMARY KEY (PK) 标识该字段为该表的主键，可以唯一的标识记录，不可以为空 UNIQUE + NOT NULL - -FOREIGN KEY (FK) 标识该字段为该表的外键，实现表与表（父表主键/子表1外键/子表2外键）之间的关联 - -NOT NULL 标识该字段不能为空 - -UNIQUE KEY (UK) 标识该字段的值是唯一的，可以为空，一个表中可以有多个UNIQUE KEY - -AUTO_INCREMENT 标识该字段的值自动增长（整数类型，而且为主键） - -DEFAULT 为该字段设置默认值 - -注意： - -​ 是否允许为空，默认NULL，可设置NOT NULL，字段不允许为空，必须赋值 - -​ 字段是否有默认值，缺省的默认值是NULL，如果插入记录时不给字段赋值，此字段使用默认值 - -```shell -MySQL [(none)]> sex enum('male','female') not null default 'male' -MySQL [(none)]> age int unsigned NOT NULL default 20 必须为正值（无符号） 不允许为空 默认是20 -``` - -​ 是否是key 主键 primary key 外键 forengn key - -#### 3.NOT NULL - -表：school.student4 - -创建表：（注意前提需要有库） - -```shell -mysql> create table school.student4( - id int not null, - name varchar(50) not null, - sex enum('m','f') default 'm' not null, - age int unsigned default 18 not null, - hobby set('music','disc','dance','book') default 'book,dance' - ); -``` - -插入数据：（注意观察查询到的数据） - -```shell -MySQL [(none)]> insert into school.student4(id,name) values(2,'robin'); -Query OK, 1 row affected (0.08 sec) - -MySQL [(none)]> select * from school.student4; -+----+-------+-----+-----+------------+ -| id | name | sex | age | hobby | -+----+-------+-----+-----+------------+ -| 2 | robin | m | 18 | dance,book | -+----+-------+-----+-----+------------+ -1 row in set (0.00 sec) -``` - -注意报错的原因： - -```shell -MySQL [(none)]> insert into school.student4 values(3,NULL,'m',40,'book'); -ERROR 1048 (23000): Column 'name' cannot be null -``` - -#### 4.唯一约束 - -作用： - -​ MySQL索引的建立对于MySQL的高效运行是很重要的，索引可以大大提高MySQL的检索速度 - -表：company.department1 - -创建表： - -```shell -MySQL [(none)]> create database company; -Query OK, 1 row affected (0.01 sec) -MySQL [(none)]> CREATE TABLE company.department1 (dept_id INT,dept_name VARCHAR(30) UNIQUE,comment VARCHAR(50)); -Query OK, 0 rows affected (0.34 sec) -``` - -查看表结构： - -```shell -MySQL [(none)]> desc company.department1; -+-----------+-------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-----------+-------------+------+-----+---------+-------+ -| dept_id | int(11) | YES | | NULL | | -| dept_name | varchar(30) | YES | UNI | NULL | | -| comment | varchar(50) | YES | | NULL | | -+-----------+-------------+------+-----+---------+-------+ -3 rows in set (0.00 sec) -``` - -数据插入：（注意查看插入数据时的提示） - -```shell -MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr"); -Query OK, 1 row affected (0.04 sec) - -MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr"); -ERROR 1062 (23000): Duplicate entry 'xingdian' for key 'dept_name' -``` - -#### 5.主键约束 - -注意：primary key 字段的值是不允许重复，且不允许不NULL（UNIQUE + NOT NULL） - -表：school.student6 - -创建表： - -```shell -MySQL [(none)]> create table school.student6( - -> id int primary key not null auto_increment, - -> name varchar(50) not null, - -> sex enum('male','female') not null default 'male', - -> age int not null default 18 - -> ); -Query OK, 0 rows affected (0.47 sec) -``` - -插入数据： - -```shell -MySQL [(none)]> insert into school.student6 values (1,'alice','female',22); -Query OK, 1 row affected (0.18 sec) - -MySQL [(none)]> insert into school.student6(name,sex,age) values - -> ('jack','male',19), - -> ('tom','male',23); -Query OK, 2 rows affected (0.14 sec) -Records: 2 Duplicates: 0 Warnings: 0 - -MySQL [(none)]> select * from school.student6; -+----+-------+--------+-----+ -| id | name | sex | age | -+----+-------+--------+-----+ -| 1 | alice | female | 22 | -| 2 | jack | male | 19 | -| 3 | tom | male | 23 | -+----+-------+--------+-----+ -3 rows in set (0.00 sec) - -``` - -## 四：修改表 - -语法格式： - -修改表名 - -​ ALTER TABLE 表名 RENAME 新表名; - -增加字段 - -​ ALTER TABLE 表名 - -​ ADD 字段名 数据类型 [完整性约束条件…], - -​ ADD 字段名 数据类型 [完整性约束条件…]; - -​ ALTER TABLE 表名 - -​ ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名; -删除字段 - -​ ALTER TABLE 表名 DROP 字段名; - -修改字段 - -​ ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…]; - -​ ALTER TABLE 表名 CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…]; - -​ ALTER TABLE 表名 CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…]; - -#### 1.修改数据库引擎 - -```shell -mysql> alter table service engine=innodb; //engine=myisam|memory|.... -``` - -#### 2.添加字段 - -```shell -mysql> create table student10 (id int); -mysql> alter table student10 add name varchar(20) not null, add age int not null default 22; - -mysql> alter table student10 add stu_num int not null after name; //添加name字段之后 - -mysql> alter table student10 add sex enum('male','female') default 'male' first; //添加到最前面 -``` - -#### 3.删除字段 - -```shell -mysql> alter table student10 drop sex; -``` - -#### 4.修改字段类型 - -```shell -MySQL [school]> desc student10; -+-------+---------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+---------+------+-----+---------+-------+ -| id | int(11) | YES | | NULL | | -| age | int(11) | YES | | NULL | | -+-------+---------+------+-----+---------+-------+ -2 rows in set (0.01 sec) - -MySQL [school]> alter table student10 modify age tinyint not null ; -Query OK, 0 rows affected (0.04 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+-------+ -| id | int(11) | YES | | NULL | | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+-------+ -2 rows in set (0.00 sec) - -MySQL [school]> alter table student10 modify id int not null primary key ; ////修改字段类型、约束、主键 -Query OK, 0 rows affected (0.02 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+-------+ -| id | int(11) | NO | PRI | NULL | | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+-------+ -``` - -#### 5.增加约束 - -```shell -MySQL [school]> alter table student10 modify id int not null primary key ; -Query OK, 0 rows affected (0.02 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+-------+ -| id | int(11) | NO | PRI | NULL | | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+-------+ -2 rows in set (0.00 sec) - -MySQL [school]> alter table student10 modify id int not null primary key auto_increment; -ERROR 1068 (42000): Multiple primary key defined //错误，该字段已经是primary key - -MySQL [school]> alter table student10 modify id int not null auto_increment; -Query OK, 0 rows affected (0.04 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+----------------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+----------------+ -| id | int(11) | NO | PRI | NULL | auto_increment | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+----------------+ -``` - -#### 6.增加主键 - -```shell -MySQL [school]> desc student1; -+-------+---------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+---------+------+-----+---------+-------+ -| id | int(11) | YES | | NULL | | -| age | int(11) | YES | | NULL | | -| name | char(1) | YES | | NULL | | -+-------+---------+------+-----+---------+-------+ -3 rows in set (0.00 sec) - -MySQL [school]> alter table student1 add primary key(id); - -MySQL [school]> desc student1; -+-------+---------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+---------+------+-----+---------+-------+ -| id | int(11) | NO | PRI | NULL | | -| age | int(11) | YES | | NULL | | -| name | char(1) | YES | | NULL | | -+-------+---------+------+-----+---------+-------+ -3 rows in set (0.00 sec) -``` - -#### 7.修改主键和自增 - -```shell -MySQL [school]> alter table student1 modify id int auto_increment; -Query OK, 0 rows affected (0.03 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student1; -+-------+---------+------+-----+---------+----------------+ -| Field | Type | Null | Key | Default | Extra | -+-------+---------+------+-----+---------+----------------+ -| id | int(11) | NO | PRI | NULL | auto_increment | -| age | int(11) | YES | | NULL | | -| name | char(1) | YES | | NULL | | -+-------+---------+------+-----+---------+----------------+ -``` - -#### 8.删除主键 - -```shell -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+----------------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+----------------+ -| id | int(11) | NO | PRI | NULL | auto_increment | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+----------------+ -2 rows in set (0.00 sec) - -MySQL [school]> alter table student10 drop primary key; -ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key - -删除自增 -ySQL [school]> alter table student10 modify id int not null; -Query OK, 0 rows affected (0.04 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+-------+ -| id | int(11) | NO | PRI | NULL | | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+-------+ - -MySQL [school]> alter table student10 drop primary key; -Query OK, 0 rows affected (0.03 sec) -Records: 0 Duplicates: 0 Warnings: 0 - -MySQL [school]> desc student10; -+-------+------------+------+-----+---------+-------+ -| Field | Type | Null | Key | Default | Extra | -+-------+------------+------+-----+---------+-------+ -| id | int(11) | NO | | NULL | | -| age | tinyint(4) | NO | | NULL | | -+-------+------------+------+-----+---------+-------+ -2 rows in set (0.00 sec) -``` - -#### 9.复制表 - -复制表结构＋记录 （key不会复制: 主键、外键和索引）复制表结构/记录+表结构，不会将Key复制 - -```shell -mysql> create table new_service select * from service; -``` - -只复制表结构 - -```shell -mysql> create table new1_service select * from service where 1=2; //条件为假，查不到任何记录 -``` - -可以复制主键,只复制表结构 - -```shell -mysql> create table t4 like employees; -``` - -#### 10.删除表 - -```shell -mysql> DROP TABLE 表名; -``` - -#### 11.修改数据表中字段的值 - -语法： - -​ Update 表名 set 列名=值where 条件 - -```shell -mysql> update student set name='123' where id=1; -``` - -删除某一行： - -​ delete from 表名 where id=1 - -```shell -mysql> delete from type where id=1; -``` - -## 五：库操作 - -#### 1.简介 - -​ 系统自带库的含义及作用 - -```shell -MySQL [(none)]> show databases; -+--------------------+ -| Database | -+--------------------+ -| information_schema | -| mysql | -| performance_schema | -| sys | -+--------------------+ -``` - -information_schema：虚拟库，主要存储了系统中的一些数据库对象的信息，例如用户表信息、列信息、权限信息、字符信息等 - -performance_schema：主要存储数据库服务器的性能参数 - -mysql：授权库，主要存储系统用户的权限信息 - -sys：主要存储数据库服务器的性能参数 - -注意：information_schema - -​ SCHEMATA 存放的是系统中的库 - -```shell -MySQL [information_schema]> select * from information_schema.SCHEMATA; -+--------------+--------------------+----------------------------+------------------------+----------+ -| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH | -+--------------+--------------------+----------------------------+------------------------+----------+ -| def | information_schema | utf8 | utf8_general_ci | NULL | -| def | mysql | latin1 | latin1_swedish_ci | NULL | -| def | performance_schema | utf8 | utf8_general_ci | NULL | -| def | school | latin1 | latin1_swedish_ci | NULL | -| def | sys | utf8 | utf8_general_ci | NULL | -+--------------+--------------------+----------------------------+------------------------+----------+ - -目录_名称 -实际库_名称 -默认_字符_设置_名称 -默认_分类_名称 -``` - -​ TABLES 存储表名 - -```shell -MySQL [information_schema]> select * from information_schema.TABLES\G -*************************** 283. row *************************** - TABLE_CATALOG: def - TABLE_SCHEMA: xingdian - TABLE_NAME: t1 - TABLE_TYPE: BASE TABLE - ENGINE: InnoDB - VERSION: 10 - ROW_FORMAT: Dynamic - TABLE_ROWS: 1 - AVG_ROW_LENGTH: 16384 - DATA_LENGTH: 16384 -MAX_DATA_LENGTH: 0 - INDEX_LENGTH: 0 - DATA_FREE: 0 - AUTO_INCREMENT: NULL - CREATE_TIME: 2022-09-22 08:18:38 - UPDATE_TIME: 2022-09-22 08:18:54 - CHECK_TIME: NULL -TABLE_COLLATION: latin1_swedish_ci - CHECKSUM: NULL - CREATE_OPTIONS: - TABLE_COMMENT: -283 rows in set (0.02 sec) -``` - -​ COLUMNS 存储字段 - -```shell -*************************** 3083. row *************************** - TABLE_CATALOG: def - TABLE_SCHEMA: xingdian - TABLE_NAME: t1 - COLUMN_NAME: id - ORDINAL_POSITION: 1 - COLUMN_DEFAULT: NULL - IS_NULLABLE: YES - DATA_TYPE: int -CHARACTER_MAXIMUM_LENGTH: NULL - CHARACTER_OCTET_LENGTH: NULL - NUMERIC_PRECISION: 10 - NUMERIC_SCALE: 0 - DATETIME_PRECISION: NULL - CHARACTER_SET_NAME: NULL - COLLATION_NAME: NULL - COLUMN_TYPE: int(11) - COLUMN_KEY: - EXTRA: - PRIVILEGES: select,insert,update,references - COLUMN_COMMENT: - GENERATION_EXPRESSION: -3083 rows in set (0.03 sec) -``` - -#### 2.创建库 - -方案一：交互式操作 - -```shell -mysql> create database xingdian; -``` - -数据库命名规则： - -​ 区分大小写 - -​ 唯一性 - -​ 不能使用关键字如 create select - -​ 不能单独使用数字 - -方案二：非交互式 - -```shell -mysql -u root -pQianFeng@123 -e "create database diandian" -``` - -#### 3.查看数据库 - -```shell -mysql> show databases; -mysql> show create database xingdian; -mysql> select database(); 查看当前所在的库 -``` - -#### 4.切换数据库 - -```shell -mysql> use xingdian; -``` - -#### 5.删除数据库 - -```shell -mysql> DROP DATABASE 数据库名; -``` +

数据库管理及数据类型

+ +**作者：行癫（盗版必究）** + +------ + +## 一：数据类型 + +#### 1.数值类型 + +##### 整数类型 + +​ 整数类型：TINYINT SMALLINT MEDIUMINT INT BIGINT + +​ 作用：用于存储用户的年龄、游戏的Level、经验值等 + +![image-20220920124821420](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124821420.png) + +##### 浮点数类型 + +​ 浮点数类型：FLOAT DOUBLE + +​ 作用：用于存储用户的身高、体重、薪水等 + +![image-20220920124919373](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124919373.png) + +```shell +float(5,3) 5宽度 3精度 +注意： + 宽度不算小数点 + 宽度-精度=点前 +案例： +MySQL [(none)]> create database diandian; +Query OK, 1 row affected (0.00 sec) + +MySQL [(none)]> use diandian +Database changed +MySQL [diandian]> create table t1(id float(6,2)); +Query OK, 0 rows affected (0.24 sec) + +MySQL [diandian]> insert into t1 values('2.22'); +``` + +##### 定点数类型 + +​ 定点数类型：DEC + +​ 定点数在MySQL内部以字符串形式存储，比浮点数更精确，适合用来表示货币等精度高的数据 + +##### 位类型 + +​ 位类型：BIT + +​ BIT(M)可以用来存放多位二进制数，M范围从1~64，如果不写默认为1位 + +#### 2.字符串类型 + +​ CHAR系列 CHAR VARCHAR + +​ TEXT系列 TINYTEXT TEXT MEDIUMTEXT LONGTEXT + +​ BLOB 系列 TINYBLOB BLOB MEDIUMBLOB LONGBLOB + +​ BINARY系列 BINARY VARBINARY + +![image-20220920132114919](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132114919.png) + +##### 枚举类型 + +​ 枚举类型：枚举列可以把一些不重复的字符串存储成一个预定义的集合 + +```shell +mysql> create table enum_table( e ENUM('fish','apple','dog')); +Query OK, 0 rows affected (0.35 sec) +mysql> insert into enum_table(e) values('fish'); +Query OK, 1 row affected (0.11 sec) + +mysql> select * from enum_table; ++------+ +| e | ++------+ +| fish | ++------+ +1 row in set (0.00 sec) + +mysql> insert into enum_table(e) values('nihao'); +ERROR 1265 (01000): Data truncated for column 'e' at row 1 +``` + +##### 时间和日期类型 + +​ 时间和日期类型：DATE TIME DATETIME TIMESTAMP YEAR + +​ 作用：用于存储用户的注册时间，文章的发布时间，文章的更新时间，员工的入职时间等 + +![image-20220920132630856](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132630856.png) + +```shell +mysql> create table t8 ( + id1 timestamp NOT NULL default CURRENT_TIMESTAMP, + id2 datetime default NULL +); + + timestamp 类型的列还有个特性：默认情况下，在 insert, update 数据时，timestamp 列会自动以当前时间（CURRENT_TIMESTAMP）填充/更新。“自动”的意思就是，你不去管它，MySQL 会替你去处理。 + +mysql> insert into t8(id1) values('20180109000000'); +mysql> select * from t8; ++---------------------+------+ +| id1 | d2 | ++---------------------+------+ +| 2018-01-09 00:00:00 | NULL | ++---------------------+------+ +1 row in set (0.00 sec) + +扩展： +select now();查看当前时间 +``` + +## 二：表操作 + +#### 1.案例 + +表:：school.student1 + +``` +字段 字段 字段 +id name sex age +1 tom male 23 记录 +2 jack male 21 记录 +3 alice female 19 记录 +``` + +语法： + +```shell +create table 表名(自定义)( + 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 +``` + +创建库表： + +```shell +mysql> CREATE DATABASE school; //创建数据库school +mysql> use school; +mysql> create table student1( + id int, + name varchar(50), + sex enum('m','f'), + age int + ); +Query OK, 0 rows affected (0.03 sec) +``` + +查看库： + +```shell +mysql> show tables; ++------------------+ +| Tables_in_school | ++------------------+ +| student1 | ++------------------+ +1 row in set (0.00 sec) +``` + +插入语法： + +``` +insert into 表名(字段1,字段2...) values(字段值列表...); +``` + +插入数据： + +```shell +mysql> insert into student1(id,name,sex,age) values(1,'xingdia','m','26'); +``` + +查看表结构： + +```shell +mysql> desc student1; ++-------+---------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+---------------+------+-----+---------+-------+ +| id | int(11) | YES | | NULL | | +| name | varchar(50) | YES | | NULL | | +| sex | enum('m','f') | YES | | NULL | | +| age | int(11) | YES | | NULL | | ++-------+---------------+------+-----+---------+-------+ +4 rows in set (0.00 sec) +``` + +查询数据： + +```shell +mysql> select id,name,sex,age from student1; //查询表中所有字段的值 +Empty set (0.00 sec) + +mysql> select * from student1; /查询表中所有字段的值 +Empty set (0.00 sec) + +mysql> select name,age from student1; //查询表中指定字段的值 +Empty set (0.00 sec) +``` + +扩展插入： + +```shell +mysql> insert into student1 values (1,'xingdian','m',33),(2,'alice','m',20),(3,'jack','m',40); //顺序插入 +Query OK, 3 rows affected (0.14 sec) +Records: 3 Duplicates: 0 Warnings: 0 + +mysql> insert into student1(name,age) values ('zhuzhu',10),('gougou',20); //只向指定的字段插入值 +Query OK, 2 rows affected (0.12 sec) +Records: 2 Duplicates: 0 Warnings: 0 +``` + +#### 2.案例 + +表：school.student2 + +```shell + 字段名 数据类型 +编号 id int +姓名 name varchar(50) +出生年份 born_year year +生日 birthday date +上课时间 class_time time +注册时间 reg_time datetime +``` + +创建表： + +```shell +mysql> create table student2( + id int, + name varchar(50), + born_year year, + birthday date, + class_time time, + reg_time datetime + ); +``` + +插入数据： + +```shell +mysql> insert into student2 values(1,'tom',now(),now(),now(),now()); +mysql> insert into student2 values(2,'jack',1982,19821120,123000,20140415162545); +``` + +表：school.student3 + +```shell +id id int +姓名 name varchar(50) +性别 sex enum('male','female') +爱好 hobby set('music','book','game','disc') +``` + +创建表： + +```shell +mysql> create table student3( + id int, + name varchar(50), + sex enum('male','female'), + hobby set('music','book','game','disc') + ); +``` + +查看表结构： + +```shell +mysql> desc student3; +mysql> show create table student3\G +``` + +插入数据： + +```shell +mysql> insert into student3 values (1,'tom','male','book,game'); +mysql> insert into student3 values (2,'jack','male','film'); +``` + +注意： + +​ DESCRIBE查看表结构 + +```shell +DESCRIBE 表名; +DESC 表名; +``` + +​ 查看表详细结构 + +```shell +SHOW CREATE TABLE 表名; +``` + +## 三：表完整性约束 + +#### 1.作用 + +​ 用于保证数据的完整性和一致性 + +#### 2.约束条件 + +PRIMARY KEY (PK) 标识该字段为该表的主键，可以唯一的标识记录，不可以为空 UNIQUE + NOT NULL + +FOREIGN KEY (FK) 标识该字段为该表的外键，实现表与表（父表主键/子表1外键/子表2外键）之间的关联 + +NOT NULL 标识该字段不能为空 + +UNIQUE KEY (UK) 标识该字段的值是唯一的，可以为空，一个表中可以有多个UNIQUE KEY + +AUTO_INCREMENT 标识该字段的值自动增长（整数类型，而且为主键） + +DEFAULT 为该字段设置默认值 + +注意： + +​ 是否允许为空，默认NULL，可设置NOT NULL，字段不允许为空，必须赋值 + +​ 字段是否有默认值，缺省的默认值是NULL，如果插入记录时不给字段赋值，此字段使用默认值 + +```shell +MySQL [(none)]> sex enum('male','female') not null default 'male' +MySQL [(none)]> age int unsigned NOT NULL default 20 必须为正值（无符号） 不允许为空 默认是20 +``` + +​ 是否是key 主键 primary key 外键 forengn key + +#### 3.NOT NULL + +表：school.student4 + +创建表：（注意前提需要有库） + +```shell +mysql> create table school.student4( + id int not null, + name varchar(50) not null, + sex enum('m','f') default 'm' not null, + age int unsigned default 18 not null, + hobby set('music','disc','dance','book') default 'book,dance' + ); +``` + +插入数据：（注意观察查询到的数据） + +```shell +MySQL [(none)]> insert into school.student4(id,name) values(2,'robin'); +Query OK, 1 row affected (0.08 sec) + +MySQL [(none)]> select * from school.student4; ++----+-------+-----+-----+------------+ +| id | name | sex | age | hobby | ++----+-------+-----+-----+------------+ +| 2 | robin | m | 18 | dance,book | ++----+-------+-----+-----+------------+ +1 row in set (0.00 sec) +``` + +注意报错的原因： + +```shell +MySQL [(none)]> insert into school.student4 values(3,NULL,'m',40,'book'); +ERROR 1048 (23000): Column 'name' cannot be null +``` + +#### 4.唯一约束 + +作用： + +​ MySQL索引的建立对于MySQL的高效运行是很重要的，索引可以大大提高MySQL的检索速度 + +表：company.department1 + +创建表： + +```shell +MySQL [(none)]> create database company; +Query OK, 1 row affected (0.01 sec) +MySQL [(none)]> CREATE TABLE company.department1 (dept_id INT,dept_name VARCHAR(30) UNIQUE,comment VARCHAR(50)); +Query OK, 0 rows affected (0.34 sec) +``` + +查看表结构： + +```shell +MySQL [(none)]> desc company.department1; ++-----------+-------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-----------+-------------+------+-----+---------+-------+ +| dept_id | int(11) | YES | | NULL | | +| dept_name | varchar(30) | YES | UNI | NULL | | +| comment | varchar(50) | YES | | NULL | | ++-----------+-------------+------+-----+---------+-------+ +3 rows in set (0.00 sec) +``` + +数据插入：（注意查看插入数据时的提示） + +```shell +MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr"); +Query OK, 1 row affected (0.04 sec) + +MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr"); +ERROR 1062 (23000): Duplicate entry 'xingdian' for key 'dept_name' +``` + +#### 5.主键约束 + +注意：primary key 字段的值是不允许重复，且不允许不NULL（UNIQUE + NOT NULL） + +表：school.student6 + +创建表： + +```shell +MySQL [(none)]> create table school.student6( + id int primary key not null auto_increment, + name varchar(50) not null, + sex enum('male','female') not null default 'male', + age int not null default 18 + ); +Query OK, 0 rows affected (0.47 sec) +``` + +插入数据： + +```shell +MySQL [(none)]> insert into school.student6 values (1,'alice','female',22); +Query OK, 1 row affected (0.18 sec) + +MySQL [(none)]> insert into school.student6(name,sex,age) values + -> ('jack','male',19), + -> ('tom','male',23); +Query OK, 2 rows affected (0.14 sec) +Records: 2 Duplicates: 0 Warnings: 0 + +MySQL [(none)]> select * from school.student6; ++----+-------+--------+-----+ +| id | name | sex | age | ++----+-------+--------+-----+ +| 1 | alice | female | 22 | +| 2 | jack | male | 19 | +| 3 | tom | male | 23 | ++----+-------+--------+-----+ +3 rows in set (0.00 sec) + +``` + +## 四：修改表 + +语法格式： + +修改表名 + +​ ALTER TABLE 表名 RENAME 新表名; + +增加字段 + +​ ALTER TABLE 表名 + +​ ADD 字段名 数据类型 [完整性约束条件…], + +​ ADD 字段名 数据类型 [完整性约束条件…]; + +​ ALTER TABLE 表名 + +​ ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名; +删除字段 + +​ ALTER TABLE 表名 DROP 字段名; + +修改字段 + +​ ALTER TABLE 表名 MODIFY 字段名 数据类型 [完整性约束条件…]; + +​ ALTER TABLE 表名 CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…]; + +​ ALTER TABLE 表名 CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…]; + +#### 1.修改数据库引擎 + +```shell +mysql> alter table service engine=innodb; //engine=myisam|memory|.... +``` + +#### 2.添加字段 + +```shell +mysql> create table student10 (id int); +mysql> alter table student10 add name varchar(20) not null, add age int not null default 22; + +mysql> alter table student10 add stu_num int not null after name; //添加name字段之后 + +mysql> alter table student10 add sex enum('male','female') default 'male' first; //添加到最前面 +``` + +#### 3.删除字段 + +```shell +mysql> alter table student10 drop sex; +``` + +#### 4.修改字段类型 + +```shell +MySQL [school]> desc student10; ++-------+---------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+---------+------+-----+---------+-------+ +| id | int(11) | YES | | NULL | | +| age | int(11) | YES | | NULL | | ++-------+---------+------+-----+---------+-------+ +2 rows in set (0.01 sec) + +MySQL [school]> alter table student10 modify age tinyint not null ; +Query OK, 0 rows affected (0.04 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+-------+ +| id | int(11) | YES | | NULL | | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+-------+ +2 rows in set (0.00 sec) + +MySQL [school]> alter table student10 modify id int not null primary key ; ////修改字段类型、约束、主键 +Query OK, 0 rows affected (0.02 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+-------+ +| id | int(11) | NO | PRI | NULL | | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+-------+ +``` + +#### 5.增加约束 + +```shell +MySQL [school]> alter table student10 modify id int not null primary key ; +Query OK, 0 rows affected (0.02 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+-------+ +| id | int(11) | NO | PRI | NULL | | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+-------+ +2 rows in set (0.00 sec) + +MySQL [school]> alter table student10 modify id int not null primary key auto_increment; +ERROR 1068 (42000): Multiple primary key defined //错误，该字段已经是primary key + +MySQL [school]> alter table student10 modify id int not null auto_increment; +Query OK, 0 rows affected (0.04 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+----------------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+----------------+ +| id | int(11) | NO | PRI | NULL | auto_increment | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+----------------+ +``` + +#### 6.增加主键 + +```shell +MySQL [school]> desc student1; ++-------+---------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+---------+------+-----+---------+-------+ +| id | int(11) | YES | | NULL | | +| age | int(11) | YES | | NULL | | +| name | char(1) | YES | | NULL | | ++-------+---------+------+-----+---------+-------+ +3 rows in set (0.00 sec) + +MySQL [school]> alter table student1 add primary key(id); + +MySQL [school]> desc student1; ++-------+---------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+---------+------+-----+---------+-------+ +| id | int(11) | NO | PRI | NULL | | +| age | int(11) | YES | | NULL | | +| name | char(1) | YES | | NULL | | ++-------+---------+------+-----+---------+-------+ +3 rows in set (0.00 sec) +``` + +#### 7.修改主键和自增 + +```shell +MySQL [school]> alter table student1 modify id int auto_increment; +Query OK, 0 rows affected (0.03 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student1; ++-------+---------+------+-----+---------+----------------+ +| Field | Type | Null | Key | Default | Extra | ++-------+---------+------+-----+---------+----------------+ +| id | int(11) | NO | PRI | NULL | auto_increment | +| age | int(11) | YES | | NULL | | +| name | char(1) | YES | | NULL | | ++-------+---------+------+-----+---------+----------------+ +``` + +#### 8.删除主键 + +```shell +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+----------------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+----------------+ +| id | int(11) | NO | PRI | NULL | auto_increment | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+----------------+ +2 rows in set (0.00 sec) + +MySQL [school]> alter table student10 drop primary key; +ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key + +删除自增 +ySQL [school]> alter table student10 modify id int not null; +Query OK, 0 rows affected (0.04 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+-------+ +| id | int(11) | NO | PRI | NULL | | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+-------+ + +MySQL [school]> alter table student10 drop primary key; +Query OK, 0 rows affected (0.03 sec) +Records: 0 Duplicates: 0 Warnings: 0 + +MySQL [school]> desc student10; ++-------+------------+------+-----+---------+-------+ +| Field | Type | Null | Key | Default | Extra | ++-------+------------+------+-----+---------+-------+ +| id | int(11) | NO | | NULL | | +| age | tinyint(4) | NO | | NULL | | ++-------+------------+------+-----+---------+-------+ +2 rows in set (0.00 sec) +``` + +#### 9.复制表 + +复制表结构＋记录 （key不会复制: 主键、外键和索引）复制表结构/记录+表结构，不会将Key复制 + +```shell +mysql> create table new_service select * from service; +``` + +只复制表结构 + +```shell +mysql> create table new1_service select * from service where 1=2; //条件为假，查不到任何记录 +``` + +可以复制主键,只复制表结构 + +```shell +mysql> create table t4 like employees; +``` + +#### 10.删除表 + +```shell +mysql> DROP TABLE 表名; +``` + +#### 11.修改数据表中字段的值 + +语法： + +​ Update 表名 set 列名=值where 条件 + +```shell +mysql> update student set name='123' where id=1; +``` + +删除某一行： + +​ delete from 表名 where id=1 + +```shell +mysql> delete from type where id=1; +``` + +## 五：库操作 + +#### 1.简介 + +​ 系统自带库的含义及作用 + +```shell +MySQL [(none)]> show databases; ++--------------------+ +| Database | ++--------------------+ +| information_schema | +| mysql | +| performance_schema | +| sys | ++--------------------+ +``` + +information_schema：虚拟库，主要存储了系统中的一些数据库对象的信息，例如用户表信息、列信息、权限信息、字符信息等 + +performance_schema：主要存储数据库服务器的性能参数 + +mysql：授权库，主要存储系统用户的权限信息 + +sys：主要存储数据库服务器的性能参数 + +注意：information_schema + +​ SCHEMATA 存放的是系统中的库 + +```shell +MySQL [information_schema]> select * from information_schema.SCHEMATA; ++--------------+--------------------+----------------------------+------------------------+----------+ +| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH | ++--------------+--------------------+----------------------------+------------------------+----------+ +| def | information_schema | utf8 | utf8_general_ci | NULL | +| def | mysql | latin1 | latin1_swedish_ci | NULL | +| def | performance_schema | utf8 | utf8_general_ci | NULL | +| def | school | latin1 | latin1_swedish_ci | NULL | +| def | sys | utf8 | utf8_general_ci | NULL | ++--------------+--------------------+----------------------------+------------------------+----------+ + +目录_名称 +实际库_名称 +默认_字符_设置_名称 +默认_分类_名称 +``` + +​ TABLES 存储表名 + +```shell +MySQL [information_schema]> select * from information_schema.TABLES\G +*************************** 283. row *************************** + TABLE_CATALOG: def + TABLE_SCHEMA: xingdian + TABLE_NAME: t1 + TABLE_TYPE: BASE TABLE + ENGINE: InnoDB + VERSION: 10 + ROW_FORMAT: Dynamic + TABLE_ROWS: 1 + AVG_ROW_LENGTH: 16384 + DATA_LENGTH: 16384 +MAX_DATA_LENGTH: 0 + INDEX_LENGTH: 0 + DATA_FREE: 0 + AUTO_INCREMENT: NULL + CREATE_TIME: 2022-09-22 08:18:38 + UPDATE_TIME: 2022-09-22 08:18:54 + CHECK_TIME: NULL +TABLE_COLLATION: latin1_swedish_ci + CHECKSUM: NULL + CREATE_OPTIONS: + TABLE_COMMENT: +283 rows in set (0.02 sec) +``` + +​ COLUMNS 存储字段 + +```shell +*************************** 3083. row *************************** + TABLE_CATALOG: def + TABLE_SCHEMA: xingdian + TABLE_NAME: t1 + COLUMN_NAME: id + ORDINAL_POSITION: 1 + COLUMN_DEFAULT: NULL + IS_NULLABLE: YES + DATA_TYPE: int +CHARACTER_MAXIMUM_LENGTH: NULL + CHARACTER_OCTET_LENGTH: NULL + NUMERIC_PRECISION: 10 + NUMERIC_SCALE: 0 + DATETIME_PRECISION: NULL + CHARACTER_SET_NAME: NULL + COLLATION_NAME: NULL + COLUMN_TYPE: int(11) + COLUMN_KEY: + EXTRA: + PRIVILEGES: select,insert,update,references + COLUMN_COMMENT: + GENERATION_EXPRESSION: +3083 rows in set (0.03 sec) +``` + +#### 2.创建库 + +方案一：交互式操作 + +```shell +mysql> create database xingdian; +``` + +数据库命名规则： + +​ 区分大小写 + +​ 唯一性 + +​ 不能使用关键字如 create select + +​ 不能单独使用数字 + +方案二：非交互式 + +```shell +mysql -u root -pQianFeng@123 -e "create database diandian" +``` + +#### 3.查看数据库 + +```shell +mysql> show databases; +mysql> show create database xingdian; +mysql> select database(); 查看当前所在的库 +``` + +#### 4.切换数据库 + +```shell +mysql> use xingdian; +``` + +#### 5.删除数据库 + +```shell +mysql> DROP DATABASE 数据库名; +```