mysql-SQL语句的使用（第八章）

2022-09-22 15:07:42

SQL语句
DDL 数据定义语言
create, drop, alter
DML 数据操纵语言
insert, delete, select, update
DCL 数据控制语言
grant, revoke

使用ALTER TABLE修改表结构

修改表名称

ALTER TABLE <表名> RENAME <新表名>

mysql> ALTER TABLE game_account RENAME account;

修改表的存储引擎

mysql> ALTER TABLE account ENGINE=MyISAM;

添加字段

ALTER TABLE <表名> ADD <字段名称> <字段定义>

mysql> ALTER TABLE account ADD Account_gender ENUM("M","F") NOT NULL;

mysql> ALTER TABLE account ADD Game_zone VARCHAR(20) NOT NULL DEFAULT "HuaBei" FIRST;

mysql> ALTER TABLE account ADD Account_money BIGINT AFTER Account_level;

删除字段

ALTER TABLE <表名> DROP <字段名称>

mysql> ALTER TABLE account DROP Account_role ;

修改字段名称及字段定义

ALTER TABLE <表名> CHANGE <旧字段名称> <新字段名称> <字段定义>

mysql> ALTER TABLE account CHANGE Account_password password CHAR(25) NOT NULL;

mysql> ALTER TABLE account CHANGE password password VARCHAR(60) ;

修改字段定义

ALTER TABLE <表名> MODIFY <字段名称> <字段定义>

mysql> ALTER TABLE account MODIFY Account_name VARCHAR(20) NOT NULL;

DML 数据操纵语言

1、添加数据 INSERT INTO

INSERT INTO tb_name(字段1名称,字段2名称,....) VALUES(value1,value2,....)

注意：
字段的数据类型是字符型、日期/时间型，对应的值需要使用双引号、单引号

插入单条数据

mysql> INSERT INTO account(Account_name,Account_password, Account_level) VALUES("king","123456",60);

插入多条数据

mysql> INSERT INTO account(Account_name ,Account_password, Account_level) VALUES("queen","123",1),("son", "redhat", 2),("sunzi","456",1);

向表中所有字段插入数据

mysql> INSERT INTO account VALUES("haha","linux",10,25000000,"F");

2、删除数据

DELETE FROM <tb_name> WHERE

mysql> DELETE FROM account WHERE Account_name="haha";

3、更新数据

UPDATE <tb_name> SET <字段名称>=<新值> WHERE <条件>

mysql> UPDATE account SET Account_password = "1q2w3e4r..1" WHERE Account_name = "king";

数据查询 --- SELECT

单表查询
多表查询/连接查询
子查询/嵌套查询

导入jiaowu数据库

[root@node01 ~]# mysql -u root -p < jiaowu.sql
Enter password:

单表查询

SELECT col_name1, col_name2, .... FROM tb_name [select_statement]

mysql> SELECT * FROM tutors;

mysql> SELECT Tname,Age FROM tutors;

mysql> SELECT Tname AS 教师, Age AS 年龄 FROM tutors; >>>设置字段的别名
mysql> SELECT Tname 教师, Age 年龄 FROM tutors;

select_statement查询子句：

1、按指定的条件查询数据

WHERE condition

条件的写法：

数字操作符：	=, !=, >, >=, <, <=

逻辑操作符：	AND， OR

mysql> SELECT * FROM tutors WHERE Age > 80;

mysql> SELECT * FROM tutors WHERE Age >= 70 AND Age <= 80;

BETWEEN n AND m

mysql> SELECT * FROM tutors WHERE Age BETWEEN 70 AND 80;

mysql> SELECT * FROM tutors WHERE Tname = "OuYangfeng" OR Tname = "YiDeng" OR Tname = "HuYidao";

IN(value1,value2,value3)

mysql> SELECT * FROM tutors WHERE Tname IN("OuYangfeng","YiDeng","HuYidao");

模糊查询

方法1)

LIKE "通配符表达式"

	通配符：
		%	任意长度任意字符
		_	任意单个字符

mysql> SELECT * FROM tutors WHERE Tname LIKE "%ang%";

mysql> SELECT * FROM tutors WHERE Tname LIKE "Y%" OR Tname LIKE "H%";

方法2)

RLIKE "正则表达式"

mysql> SELECT * FROM tutors WHERE Tname RLIKE "^[1]";

mysql> SELECT * FROM tutors WHERE Tname RLIKE "ang";

IS NULL/IS NOT NULL

mysql> SELECT * FROM students WHERE TID IS NULL;

2、按指定的字段内容排序

ORDER BY <col_name> [ASC|DESC]

	DESC：降序
	ASC：升序，默认

mysql> SELECT * FROM tutors ORDER BY Age;

mysql> SELECT * FROM tutors ORDER BY Age DESC;

3、限制结果的输出行数

LIMIT [n,]m

	忽略前n行，共显示m行

mysql> SELECT * FROM tutors LIMIT 3;

mysql> SELECT * FROM tutors LIMIT 2,3;

mysql> SELECT * FROM tutors ORDER BY Age LIMIT 1;

mysql> SELECT * FROM tutors WHERE Gender="M" ORDER BY Age DESC LIMIT 1;

4、按指定字段将数据进行分组

GROUP BY <字段名称> [HAVING <条件>]

聚合函数：

SUM(字段名称)		求和
AVG(字段名称)		平均值
MAX(字段名称)		最大值
MIN(字段名称)		最小值
COUNT(字段名称)		计数

mysql> SELECT AVG(Age) AS 平均年龄 FROM tutors;

mysql> SELECT AVG(Age) AS 平均年龄,Gender AS 性别 FROM tutors GROUP BY Gender;

mysql> SELECT AVG(Age) AS 平均年龄,Gender AS 性别 FROM tutors GROUP BY Gender HAVING 平均年龄>65;

连接查询(多表查询)

内连接
外连接
	左外连接
	右外连接

前提条件：多张表之间要存在相关联的字段

内连接

特征：只有相关联字段具有相同的值时，才显示对应的结果 

语法：

	SELECT tb1.col, tb2.col,.... FROM tb1 INNER JOIN tb2 ON tb1.col=tb2.col

mysql> SELECT students.Name, students.Age, students.Gender, courses.Cname
-> FROM students INNER JOIN courses
-> ON students.CID1=courses.CID;

mysql> SELECT students.Name, students.Age, students.Gender, tutors.Tname
-> FROM students INNER JOIN tutors
-> ON students.TID=tutors.TID;

mysql> SELECT students.Name, students.Age, students.Gender, courses.Cname, tutors.Tname
-> FROM students INNER JOIN courses INNER JOIN tutors
-> ON students.CID1=courses.CID AND courses.TID=tutors.TID;

自然连接

mysql> SELECT students.Name, students.Age, students.Gender, courses.Cname
-> FROM students,courses
-> WHERE students.CID1=courses.CID;

外连接

左外连接

特征：以左表为主，显示左表所有数据，右表中没有关联的数据时，显示为NULL

语法： 

SELECT tb1.col, tb2.col,.... FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col

mysql> SELECT students.Name, students.Age, students.Gender, courses.Cname
-> FROM students LEFT JOIN courses
-> ON students.CID2=courses.CID;

右外连接

	特征：以右表为主，显示右表所有数据，左表中没有关联的数据时，显示为NULL

	语法： 

	SELECT tb1.col, tb2.col,.... FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col

嵌套查询/子查询

以查询的结果作为另外一个查询的条件、数据源使用
	
mysql> SELECT * FROM tutors WHERE Age > (SELECT AVG(Age) FROM tutors);

用户权限控制

用户管理

格式：user@host		
	
	root@localhost
	
host写法：
	1、IP地址	martin@192.168.1.1
	2、网段		martin@192.168.1.%
	3、所有		martin@%

创建用户

CREATE USER IDENTIFIED BY

mysql> CREATE USER ‘martin‘@‘localhost‘ IDENTIFIED BY ‘Www.1.com‘;
mysql> FLUSH PRIVILEGES;

mysql> SELECT user();
+------------------+
| user() |
+------------------+
| martin@localhost |
+------------------+
1 row in set (0.00 sec)

设置用户的密码

方法1)

mysql> SET PASSWORD FOR ‘martin‘@‘localhost‘ = PASSWORD("Www.3.com");
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

方法2)

[root@node01 mysql]# mysqladmin -u martin -p password "Www.4.com"

方法3)

mysql> ALTER USER ‘martin‘@"localhost" IDENTIFIED BY "Www.2.com";
Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

存放用户信息的表 ------- mysql.user

删除用户

mysql> DROP USER ‘martin‘@‘localhost‘;

mysql> FLUSH PRIVILEGES;

权限控制

查看用户权限

mysql> SHOW GRANTS FOR ‘martin‘@‘localhost‘;

授权

GRANT <权限>,... ON <库名>.<表名> TO <用户名> [IDENTIFIED BY "password"]

权限：

	select 
	select,update,create 
	all 
	
库名.表名：

	jiaowu.tutors
	jiaowu.*
	*.*

mysql> GRANT select ON jiaowu.tutors TO ‘martin‘@‘localhost‘;
mysql> FLUSH PRIVILEGES;

mysql> GRANT select,insert ON jiaowu.* TO ‘admin‘@‘localhost‘ IDENTIFIED BY ‘Www.1.com‘;
mysql> FLUSH PRIVILEGES;

示例：建立远程登录用户alice，允许在192.168.122.137上登录数据库服务器，允许其查询jiaowu库中的tutors表，并允许其更新表中的年龄字段

mysql> GRANT select, update(Age) ON jiaowu.tutors TO ‘alice‘@‘192.168.122.137‘ IDENTIFIED BY ‘Www.1.com‘;

mysql> FLUSH PRIVILEGES;

客户端：

[root@node03 ~]# yum install -y mysql-community-client.x86_64

[root@node03 ~]# mysql -u alice -p -h 192.168.122.105

撤销权限

REVOKE <权限> ON <库名>.<表名> FROM <用户名>

mysql> REVOKE select ON jiaowu.tutors FROM "martin"@"localhost";
mysql> FLUSH PRIVILEGES;

https://dev.mysql.com/doc/refman/5.5/en/privileges-provided.html

索引Index

作用：提高查询速度

1、创建索引

mysql> CREATE INDEX account_name ON account(Account_name);

2、查看索引

mysql> SHOW INDEX FROM account\G;

3、删除索引

mysql> DROP INDEX account_name ON account;

HY ??

mysql-SQL语句的使用（第八章）

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