954 lines
26 KiB
Markdown
954 lines
26 KiB
Markdown
<h2><center>数据库管理</center></h2>
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------
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## 一：数据类型
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在MySQL数据库管理系统中，可以通过存储引擎来决定表的类型。同时，MySQL数据库管理系统也提供了数据类型决定表存储数据的类型。
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### 1. 数值类型
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**整数类型**
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整数类型：TINYINT SMALLINT MEDIUMINT INT BIGINT
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作用：用于存储用户的年龄、游戏的Level、经验值等
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**浮点数类型**
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浮点数类型：FLOAT DOUBLE
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作用：用于存储用户的身高、体重、薪水等
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```SQL
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float(5,3) # 5宽度 3精度
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注意：
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宽度不算小数点
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宽度-精度=整数
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案例：
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mysql> create database test;
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Query OK, 1 row affected (0.00 sec)
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mysql> use test
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Database changed
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mysql> create table t1(id float(6,2));
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Query OK, 0 rows affected (0.00 sec)
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mysql> insert into t1 values('2.22');
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Query OK, 1 row affected (0.02 sec)
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```
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**定点数类型**
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定点数类型：DEC
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作用：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
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**位类型**
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位类型：BIT
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作用：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
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### 2. 字符串类型
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- CHAR系列：CHAR VARCHAR
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- TEXT系列：TINYTEXT TEXT MEDIUMTEXT LONGTEXT
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- BLOB系列：TINYBLOB BLOB MEDIUMBLOB LONGBLOB
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- BINARY系列：BINARY VARBINARY
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**枚举类型**
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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
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```SQL
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mysql> create table enum_table(e ENUM('fish','apple','dog'));
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Query OK, 0 rows affected (0.01 sec)
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mysql> insert into enum_table(e) values('fish');
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Query OK, 1 row affected (0.01 sec)
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mysql> select * from enum_table;
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+------+
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| e |
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+------+
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| fish |
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+------+
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1 row in set (0.00 sec)
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mysql> insert into enum_table(e) values('nihao');
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ERROR 1265 (01000): Data truncated for column 'e' at row 1
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```
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**时间和日期类型**
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时间和日期类型：DATE、TIME、DATETIME、TIMESTAMP、YEAR
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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
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```SQL
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mysql> create table t2(
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-> id1 timestamp NOT NULL default CURRENT_TIMESTAMP,
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-> id2 datetime default NULL
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-> );
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Query OK, 0 rows affected (0.00 sec)
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mysql> insert into t2(id1) values('20250311104200');
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Query OK, 1 row affected (0.00 sec)
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mysql> select * from t2;
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+---------------------+------+
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| id1 | id2 |
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+---------------------+------+
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| 2025-03-11 10:42:00 | NULL |
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+---------------------+------+
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1 row in set (0.00 sec)
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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。
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扩展：
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mysql> select now();
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+---------------------+
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| now() |
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+---------------------+
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| 2025-03-11 10:42:44 |
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+---------------------+
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1 row in set (0.00 sec)
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```
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## 二：表操作
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**使用编辑器编辑指令**
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```SQL
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mysql> edit
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mysql> \e
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```
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**在mysql客户端内执行系统命令**
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```SQL
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mysql> system ls
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mysql> \! ls
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```
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### 1. 案例
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表：school.student1
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```
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字段 字段 字段
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id name sex age
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1 tom male 23 记录
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2 jack male 21 记录
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3 alice female 19 记录
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```
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语法：
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```SQL
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create table 表名(自定义)(
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字段名1 类型[(宽度) 约束条件],
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字段名2 类型[(宽度) 约束条件],
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字段名3 类型[(宽度) 约束条件]
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)[存储引擎 字符集];
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1.在同一张表中，字段名是不能相同
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2.宽度和约束条件可选
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3.字段名和类型是必须的
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```
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创建库表：
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```SQL
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mysql> create database school;
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Query OK, 1 row affected (0.00 sec)
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mysql> use school
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Database changed
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mysql> create table student1(
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-> id int,
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-> name varchar(50),
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-> sex enum('m','f'),
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-> age int
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-> );
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Query OK, 0 rows affected (0.01 sec)
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```
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查看库：
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```SQL
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mysql> show tables;
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+------------------+
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| Tables_in_school |
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+------------------+
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| student1 |
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+------------------+
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1 row in set (0.00 sec)
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```
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插入语法：
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```SQL
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insert into 表名(字段1,字段2...) values(字段值列表...);
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```
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插入数据：
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```SQL
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mysql> insert into student1(id,name,sex,age) values(1,'wxin','m',26);
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Query OK, 1 row affected (0.01 sec)
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```
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查看表结构：
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```SQL
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mysql> desc student1;
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+-------+---------------+------+-----+---------+-------+
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| Field | Type | Null | Key | Default | Extra |
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+-------+---------------+------+-----+---------+-------+
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| id | int(11) | YES | | NULL | |
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| name | varchar(50) | YES | | NULL | |
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| sex | enum('m','f') | YES | | NULL | |
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| age | int(11) | YES | | NULL | |
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+-------+---------------+------+-----+---------+-------+
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4 rows in set (0.00 sec)
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mysql> show create table student1;
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mysql> show table status like 'student1' \G
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```
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查询数据：
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```SQL
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mysql> select id,name,sex,age from student1; //查询表中所有字段的值
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+------+------+------+------+
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| id | name | sex | age |
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+------+------+------+------+
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| 1 | wxin | m | 26 |
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+------+------+------+------+
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1 row in set (0.00 sec)
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mysql> select * from student1; //查询表中所有字段的值
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+------+------+------+------+
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| id | name | sex | age |
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+------+------+------+------+
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| 1 | wxin | m | 26 |
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+------+------+------+------+
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1 row in set (0.00 sec)
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mysql> select name,age from student1; //查询表中指定字段的值
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+------+------+
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| name | age |
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+------+------+
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| wxin | 26 |
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+------+------+
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1 row in set (0.00 sec)
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```
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扩展插入：
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```SQL
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mysql> insert into student1 values(2,'wyu','f',25),(3,'wyi','m',24),(4,'wbo','m',23); //顺序插入
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Query OK, 3 rows affected (0.00 sec)
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Records: 3 Duplicates: 0 Warnings: 0
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mysql> insert into student1(name,age) values('zhangsan',22),('lisi',21);
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Query OK, 2 rows affected (0.00 sec)
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Records: 2 Duplicates: 0 Warnings: 0
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```
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### 2. 案例
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表：school.student2
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```
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字段名 数据类型
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编号 id int
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姓名 name varchar(50)
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出生年份 born_year year
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生日 birthday date
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上课时间 class_time time
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注册时间 reg_time datetime
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```
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创建表：
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```SQL
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mysql> create table student2(
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-> id int,
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-> name varchar(50),
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-> born_year year,
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-> birthday date,
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-> class_time time,
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-> reg_time datetime
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-> );
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Query OK, 0 rows affected (0.00 sec)
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```
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插入数据：
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```SQL
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mysql> insert into student2 values(1,'tom',now(),now(),now(),now());
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Query OK, 1 row affected, 1 warning (0.00 sec)
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mysql> insert into student2 values(2,'jack',1982,19821120,123000,20140415162545);
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Query OK, 1 row affected (0.00 sec)
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```
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表：school.student3
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```
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id id int
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姓名 name varchar(50)
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性别 sex enum('male','female')
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爱好 hobby set('music','book','game','disc')
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```
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创建表：
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```SQL
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mysql> create table student3(
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-> id int,
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-> name varchar(50),
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-> sex enum('m','f'),
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-> hobby set('music','book','game','disc')
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-> );
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Query OK, 0 rows affected (0.00 sec)
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```
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查看表结构：
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```SQL
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mysql> desc student3;
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+-------+-----------------------------------+------+-----+---------+-------+
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| Field | Type | Null | Key | Default | Extra |
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+-------+-----------------------------------+------+-----+---------+-------+
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| id | int(11) | YES | | NULL | |
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| name | varchar(50) | YES | | NULL | |
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| sex | enum('m','f') | YES | | NULL | |
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| hobby | set('music','book','game','disc') | YES | | NULL | |
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+-------+-----------------------------------+------+-----+---------+-------+
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4 rows in set (0.00 sec)
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mysql> show create table student3\G
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*************************** 1. row ***************************
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Table: student3
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Create Table: CREATE TABLE `student3` (
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`id` int(11) DEFAULT NULL,
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`name` varchar(50) DEFAULT NULL,
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`sex` enum('m','f') DEFAULT NULL,
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`hobby` set('music','book','game','disc') DEFAULT NULL
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) ENGINE=InnoDB DEFAULT CHARSET=utf8
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1 row in set (0.00 sec)
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```
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插入数据：
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```SQL
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mysql> insert into student3 values(1,'tom','m','book,game');
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Query OK, 1 row affected (0.00 sec)
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mysql> insert into student3 values(2,'jack','m','film');
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ERROR 1265 (01000): Data truncated for column 'hobby' at row 1
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```
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注意：
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DESCRIBE查看表结构
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```SQL
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DESCRIBE 表名;
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DESC 表名;
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```
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查看表详细结构：
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```SQL
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SHOW CREATE TABLE 表名;
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```
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## 三：表完整性约束
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### 1. 作用
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用于保证数据的完整性和一致性
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### 2. 约束条件
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- RPIMARY 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
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- 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
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- NOT NULL：标识该字段不能为空
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- 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
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- AUTO_INCREMENT：标识该字段的值自动增长（整数类型，而且为主键）
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- DEFAULT：该字段设置默认值
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注意：
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- 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
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- 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
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```SQL
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mysql> sex enum('male','female') not null default 'male'
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mysql> age int unsigned NOT NULL default 20
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必须为正值（无符号） 不允许为空 默认是20
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```
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是否是key 主键 primary key 外键 forengn key
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### 3. NOT NULL
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表：school.student4
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创建表：
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```SQL
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mysql> create table student4(
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-> id int not null,
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-> name varchar(50) not null,
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-> sex enum('m','f') default 'm' not null,
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-> age int unsigned default 18 not null,
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-> hobby set('music','disc','dance','book') default 'book,dance'
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-> );
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Query OK, 0 rows affected (0.01 sec)
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```
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插入数据：（注意观察查询到的数据）
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```SQL
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mysql> insert into student4(id,name) values(2,'robin');
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Query OK, 1 row affected (0.00 sec)
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mysql> select * from student4;
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+----+-------+-----+-----+------------+
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| id | name | sex | age | hobby |
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+----+-------+-----+-----+------------+
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| 2 | robin | m | 18 | dance,book |
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+----+-------+-----+-----+------------+
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1 row in set (0.00 sec)
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```
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注意报错的原因：
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```SQL
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mysql> insert into student4 values(3,null,'m',40,'book');
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ERROR 1048 (23000): Column 'name' cannot be null
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```
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### 4. 唯一约束
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作用：
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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
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表：company.department
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创建表：
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```SQL
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mysql> create database company;
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Query OK, 1 row affected (0.00 sec)
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mysql> create table company.department1(
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-> dept_id int,
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-> dept_name varchar(30) UNIQUE,
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-> comment varchar(50)
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-> );
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Query OK, 0 rows affected (0.00 sec)
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```
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查看表结构：
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```SQL
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mysql> desc company.department1;
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+-----------+-------------+------+-----+---------+-------+
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| Field | Type | Null | Key | Default | Extra |
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+-----------+-------------+------+-----+---------+-------+
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| dept_id | int(11) | YES | | NULL | |
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| dept_name | varchar(30) | YES | UNI | NULL | |
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| comment | varchar(50) | YES | | NULL | |
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+-----------+-------------+------+-----+---------+-------+
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3 rows in set (0.00 sec)
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```
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数据插入：（注意查看插入数据时的提示）
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```SQL
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mysql> insert into company.department1 values(1,'zhangsan','hr');
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Query OK, 1 row affected (0.00 sec)
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mysql> insert into company.department1 values(1,'zhangsan','hr');
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ERROR 1062 (23000): Duplicate entry 'zhangsan' for key 'dept_name'
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```
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### 5. 主键约束
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注意：
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primary key字段的值是不允许重复，且不允许不NULL（UNIQUE + NOT NULL）
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表：school.student6
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创建表：
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```SQL
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mysql> create table school.student6(
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-> id int primary key not null auto_increment,
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-> name varchar(50) not null,
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-> sex enum('m','f') not null default 'm',
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-> age int not null default 18
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-> );
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Query OK, 0 rows affected (0.01 sec)
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```
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插入数据：
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```SQL
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mysql> insert into school.student6 values (1,'alice','f',22);
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Query OK, 1 row affected (0.00 sec)
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mysql> insert into school.student6(name,sex,age) values ('jack','m',19),('tom','m',23);
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Query OK, 2 rows affected (0.00 sec)
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Records: 2 Duplicates: 0 Warnings: 0
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mysql> select * from school.student6;
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+----+-------+-----+-----+
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| id | name | sex | age |
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+----+-------+-----+-----+
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| 1 | alice | f | 22 |
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| 2 | jack | m | 19 |
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| 3 | tom | m | 23 |
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+----+-------+-----+-----+
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3 rows in set (0.00 sec)
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```
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## 四：修改表
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语法格式：
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- 修改表名
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1. alter table 表名 rename 新表名
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2. rename table 新表名 to 表名
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|
||
- 增加字段
|
||
|
||
1. 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...];
|
||
|
||
2. 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
|
||
|
||
1. alter table 表名 modify 字段名 数据类型 [完整性约束条件...];
|
||
2. 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...];
|
||
3. alter table 表名 change 旧字段名 新字段名 新数据类型 [完整性数据约束...]：
|
||
|
||
### 1. 修改数据库引擎
|
||
|
||
```SQL
|
||
mysql> alter table student2 engine=myisam;
|
||
Query OK, 2 rows affected (0.01 sec)
|
||
Records: 2 Duplicates: 0 Warnings: 0
|
||
//engine=innodb|memory|....
|
||
```
|
||
|
||
### 2. 添加字段
|
||
|
||
```SQL
|
||
mysql> create table student5(id int);
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
|
||
mysql> alter table student5 add name varchar(30) not null,add age int not null default 22;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> alter table student5 add stu_num int not null after name;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> alter table student5 add sex enum('m','f') default 'm' first;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
```
|
||
|
||
### 3. 删除字段
|
||
|
||
```SQL
|
||
mysql> alter table student5 drop sex;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
```
|
||
|
||
### 4. 修改字段类型
|
||
|
||
```SQL
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| id | int(11) | YES | | NULL | |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | int(11) | NO | | 22 | |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
4 rows in set (0.00 sec)
|
||
|
||
mysql> alter table student5 modify age tinyint not null;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| id | int(11) | YES | | NULL | |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
4 rows in set (0.01 sec)
|
||
|
||
mysql> alter table student5 modify id int not null primary key;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
4 rows in set (0.00 sec)
|
||
```
|
||
|
||
### 5. 增加约束
|
||
|
||
```SQL
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
4 rows in set (0.00 sec)
|
||
|
||
mysql> alter table student5 modify id int not null auto_increment;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student5; +---------+-------------+------+-----+---------+----------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+----------------+
|
||
| id | int(11) | NO | PRI | NULL | auto_increment |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+----------------+
|
||
4 rows in set (0.00 sec)
|
||
```
|
||
|
||
### 6. 增加主键
|
||
|
||
```SQL
|
||
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)
|
||
|
||
mysql> alter table student1 add primary key(id);
|
||
Query OK, 0 rows affected (0.03 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student1;
|
||
+-------+---------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+---------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(50) | YES | | NULL | |
|
||
| sex | enum('m','f') | YES | | NULL | |
|
||
| age | int(11) | YES | | NULL | |
|
||
+-------+---------------+------+-----+---------+-------+
|
||
4 rows in set (0.00 sec)
|
||
```
|
||
|
||
### 7. 修改主键和自增
|
||
|
||
```SQL
|
||
mysql> alter table student1 modify id int auto_increment;
|
||
Query OK, 4 rows affected (0.00 sec)
|
||
Records: 4 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student1;
|
||
+-------+---------------+------+-----+---------+----------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+-------+---------------+------+-----+---------+----------------+
|
||
| id | int(11) | NO | PRI | NULL | auto_increment |
|
||
| name | varchar(50) | YES | | NULL | |
|
||
| sex | enum('m','f') | YES | | NULL | |
|
||
| age | int(11) | YES | | NULL | |
|
||
+-------+---------------+------+-----+---------+----------------+
|
||
4 rows in set (0.00 sec)
|
||
```
|
||
|
||
### 8. 删除主键
|
||
|
||
```SQL
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+----------------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+----------------+
|
||
| id | int(11) | NO | PRI | NULL | auto_increment |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+----------------+
|
||
4 rows in set (0.00 sec)
|
||
|
||
mysql> alter table student5 drop primary key;
|
||
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
|
||
mysql> alter table student5 modify id int not null;
|
||
Query OK, 0 rows affected (0.01 sec)
|
||
Records: 0 Duplicates: 0 Warnings: 0
|
||
|
||
mysql> desc student5;
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| Field | Type | Null | Key | Default | Extra |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
| id | int(11) | NO | PRI | NULL | |
|
||
| name | varchar(30) | NO | | NULL | |
|
||
| stu_num | int(11) | NO | | NULL | |
|
||
| age | tinyint(4) | NO | | NULL | |
|
||
+---------+-------------+------+-----+---------+-------+
|
||
4 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
|
||
|
||
```SQL
|
||
mysql> create table new_service select * from service;
|
||
```
|
||
|
||
只复制表结构
|
||
|
||
```SQL
|
||
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
|
||
|
||
```SQL
|
||
mysql> create table t4 like employees;
|
||
```
|
||
|
||
### 10. 删除表
|
||
|
||
```SQL
|
||
mysql> DROP TABLE 表名;
|
||
|
||
mysql> show tables;
|
||
+------------------+
|
||
| Tables_in_school |
|
||
+------------------+
|
||
| student1 |
|
||
| student2 |
|
||
| student3 |
|
||
| student4 |
|
||
| student5 |
|
||
| student6 |
|
||
+------------------+
|
||
6 rows in set (0.00 sec)
|
||
|
||
mysql> drop table student5;
|
||
Query OK, 0 rows affected (0.00 sec)
|
||
|
||
mysql> show tables;
|
||
+------------------+
|
||
| Tables_in_school |
|
||
+------------------+
|
||
| student1 |
|
||
| student2 |
|
||
| student3 |
|
||
| student4 |
|
||
| student6 |
|
||
+------------------+
|
||
5 rows in set (0.00 sec)
|
||
```
|
||
|
||
### 11. 修改数据表中字段的值
|
||
|
||
语法：
|
||
|
||
update 表名 set 列名=值 where 条件
|
||
|
||
```SQL
|
||
mysql> update student set name='123' where id=1;
|
||
```
|
||
|
||
### 12. 删除某一行
|
||
|
||
语法：
|
||
|
||
delete from 表名 where id = 1
|
||
|
||
```SQL
|
||
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
|
||
|
||
```SQL
|
||
mysql> show databases;
|
||
+--------------------+
|
||
| Database |
|
||
+--------------------+
|
||
| information_schema |
|
||
| mysql |
|
||
| performance_schema |
|
||
| sys |
|
||
+--------------------+
|
||
7 rows in set (0.00 sec)
|
||
```
|
||
|
||
- 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
|
||
|
||
```SQL
|
||
mysql> 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 | company | utf8 | utf8_general_ci | NULL |
|
||
| def | mysql | utf8 | utf8_general_ci | NULL |
|
||
| def | performance_schema | utf8 | utf8_general_ci | NULL |
|
||
| def | school | utf8 | utf8_general_ci | NULL |
|
||
| def | sys | utf8 | utf8_general_ci | NULL |
|
||
| def | test | utf8 | utf8_general_ci | NULL |
|
||
+--------------+--------------------+----------------------------+------------------------+----------+
|
||
7 rows in set (0.00 sec)
|
||
|
||
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
|
||
|
||
```SQL
|
||
mysql> select * from information_schema.TABLES\G
|
||
*************************** 1. row ***************************
|
||
TABLE_CATALOG: def
|
||
TABLE_SCHEMA: information_schema
|
||
TABLE_NAME: CHARACTER_SETS
|
||
TABLE_TYPE: SYSTEM VIEW
|
||
ENGINE: MEMORY
|
||
VERSION: 10
|
||
ROW_FORMAT: Fixed
|
||
TABLE_ROWS: NULL
|
||
AVG_ROW_LENGTH: 384
|
||
DATA_LENGTH: 0
|
||
MAX_DATA_LENGTH: 16434816
|
||
INDEX_LENGTH: 0
|
||
DATA_FREE: 0
|
||
AUTO_INCREMENT: NULL
|
||
CREATE_TIME: 2025-03-11 12:37:46
|
||
UPDATE_TIME: NULL
|
||
CHECK_TIME: NULL
|
||
TABLE_COLLATION: utf8_general_ci
|
||
CHECKSUM: NULL
|
||
CREATE_OPTIONS: max_rows=43690
|
||
TABLE_COMMENT:
|
||
```
|
||
|
||
|
||
|
||
### 2. 创建库
|
||
|
||
方案一：交互式操作
|
||
|
||
```SQL
|
||
mysql> create database wxin;
|
||
Query OK, 1 row affected (0.00 sec)
|
||
```
|
||
|
||
方案二：非交互式
|
||
|
||
```bash
|
||
[root@rpm mysql]# ./bin/mysql -uroot -p'Wfahui@3123' -e "create database wxin";
|
||
```
|
||
|
||
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
|
||
|
||
**sql语句结尾**
|
||
|
||
每条sql语句都要以;结尾，但是如果列比较多，想看的清楚一点，可以以\G结尾
|
||
|
||
### 3. 查看数据库
|
||
|
||
```SQL
|
||
mysql> show databases;
|
||
mysql> show create database wxin;
|
||
mysql> select database(); 查看当前所在的库
|
||
```
|
||
|
||
### 4.切换数据库
|
||
|
||
```SQL
|
||
mysql> use wxin
|
||
```
|
||
|
||
### 5. 删除数据库
|
||
|
||
```SQL
|
||
mysql> DROP DATABASE 数据库名;
|
||
```
|
||
|