MYSQL基本操作语句

时间：2023-03-09 09:09:37
MYSQL基本操作语句

0、修改密码:mysqladmin -u root -p password 123456

导出数据库：mysqldump -u root -p yunpay>yunpay.sql

导入数据库：mysql –u root -p yunpay < yunpay.sql

1、为mysql增加一个名为admin，主机名任意的网络用户，其通过密码'123'访问数据库，这个用户拥有对数据库的所有操作权限（ALL PRIVILEGES）

CREATE USER 'admin'@'%' IDENTIFIED BY '123';
GRANT ALL PRIVILEGES ON * . * TO 'admin'@'%' IDENTIFIED BY '123' WITH GRANT OPTION;

2、删除该用户

DROP USER 'wbhuang'@'%';

3、创建数据库

CREATE DATABASE school;
USE school;
SHOW TABLES;

4、删除、创建数据表

删除数据表时，有如下语法

DROP TABLE <表名> [RESTRICT | CASCADE];

当选择RESTRICT：则该表的删除是有限制条件的。欲删除的基本表不能被其他表的约束所引用（如CHECK，FOREIGN KEY等约束），不能有视图，触发器，存储过程和函数，否则不能删除。如果选择CASCADE：则删除基本表的同事，相关的依赖对象，例如视图，都将被一起删除。下面语句的"SET FOREGIN_KEY_CHECKS = 0;"为取消CHECKS依赖。可见MYSQL默认的删除表方式为RESTRICT（受约束的）。

SET FOREIGN_KEY_CHECKS = 0;
DROP TABLE IF EXISTS Student;
DROP TABLE IF EXISTS Course;
DROP TABLE IF EXISTS SC;
CREATE TABLE Student
    (Sno CHAR(9) PRIMARY KEY,
     Sname CHAR(20) UNIQUE,
         Ssex CHAR(2),
         Sage SMALLINT,
         Sdept CHAR(20)
        );
         
CREATE TABLE Course
    (Cno CHAR(4) PRIMARY KEY,
         Cname CHAR(40),
         Cpno CHAR(4),/*先修课*/
         Ccredit SMALLINT,
         FOREIGN KEY (Cpno) REFERENCES Course(Cno)
         /*表级完整性约束条件，Cpno是外码，被参照表是Course，被参照列是Cno*/
         );
CREATE TABLE SC
    (Sno CHAR(9),
         Cno CHAR(4),
         Grade SMALLINT,
         PRIMARY KEY (Sno,Cno),
         /*主码由两个属性构成，必须作为表级完整性进行定义*/
         FOREIGN KEY (Sno) REFERENCES Student(Sno),
         FOREIGN KEY (Cno) REFERENCES Course(Cno)
        );

5、修改数据表

ALTER TABLE Student DROP COLUMN Sentry;
ALTER TABLE Student ADD Sentrance DATE;
ALTER TABLE Student CHANGE Sentrance Sentry DATE;
/*为Student增加"入学时间"列*/
ALTER TABLE Student MODIFY COLUMN Sage INT;
/*将年龄的数据类型由字符型改为整形*/
ALTER TABLE Course ADD UNIQUE(Cname);
/*增加课程名称必须取唯一值的约束条件*/

6、删除、创建索引表

DROP INDEX Stusno ON Student;
DROP INDEX Coucno ON Course;
DROP INDEX SCno ON SC;
CREATE UNIQUE INDEX Stusno ON Student(Sno);
/*按课程号升序建唯一索引*/
CREATE UNIQUE INDEX Coucno ON Course(Cno);
/*SC表按学号升序和课程号降序建唯一索引*/
CREATE UNIQUE INDEX SCno ON SC(Sno ASC, Cno DESC);
<br>SELECT * FROM INDEX Stusno;

7、插入数据

INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept,Sentry) VALUES('20071025','wbhuang','male',23,'math','2007-09-01');
INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept,Sentry) VALUES('20071026','dkluo','male',24,'math','2007-09-01');
INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept,Sentry) VALUES('20071005','hlyang','male',24,'math','2007-09-01');
INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept,Sentry) VALUES('20071007','ljhu','male',24,'math','2007-09-01');
INSERT INTO Student (Sno,Sname,Ssex,Sage,Sdept,Sentry) VALUES('20071024','yluo','male',24,'math','2007-09-01');
INSERT INTO Course (Cno,Cname,Cpno,Ccredit) VALUES('100','Chinese','100',4);
INSERT INTO Course (Cno,Cname,Cpno,Ccredit) VALUES('101','English','100',3);
INSERT INTO Course (Cno,Cname,Cpno,Ccredit) VALUES('102','Science','100',2);
INSERT INTO Course (Cno,Cname,Cpno,Ccredit) VALUES('103','Math','100',5);

8、修改、删除数据

UPDATE  `school`.`student` SET  `Sname` =  'wbhuang',`Sdept` =  'xinji' WHERE  `student`.`Sno` =  '20071025';
DELETE FROM Student WHERE Sno='20071025';

9、普通查询和聚集函数

SELECT Sno,Sname,Ssex FROM Student WHERE Sno='20071004';
SELECT COUNT(DISTINCT Sname) FROM Student;
SELECT AVG(Sage) FROM Student;
SELECT Cno FROM Student ORDER BY Sage DESC;
ORDER BY <列名|,列名> [ASC | DESC];       ASC升序，DESC降序
COUNT([DISTINCT | ALL] * )          统计元素个数
COUNT([DISTINCT | ALL] <列名> ) 统计一列中元素个数
SUM([DISTINCT | ALL] <列名> )       计算一列值的总和（数值型）
AVG([DISTINCT | ALL] <列名> )       计算一列值的平均值（数值型）
MAX([DISTINCT | ALL] <列名> )       计算一列值的最大值
MIX([DISTINCT | ALL] <列名> )       计算一列值的最小值
GROUP BY 子句将查询结果按某一列或多列的值分组，值相等的为一组。
SELECT Cno,COUNT(Sno) FROM SC GROUP BY Cno;
/*Cno值相等的为一组，计算各组的COUNT(Sno)*/

10、连接查询

/*等值，非等值连接：比较的连接谓词有=、<、>、>=、<=、!=(或<>)等*/
SELECT Student.*,SC.* FROM Student,SC WHERE Student.Sno=SC.Sno;
/*若在等值连接中把目标列的重复的属性去掉则为自然连接*/
SELECT Student.*,SC.Cno,SC.Grade FROM Student,SC WHERE Student.Sno=SC.Sno;
/*自身连接：一个表与自己进行连接*/
SELECT FIRST.*,SECOND.* FROM Course FIRST, Course SECOND WHERE FIRST.Cpno=SECOND.Cno;
/*外连接：若某个Student没有选课，仍把舍弃的Student元组保存在结果中，其SC的属性全填NULL*/
SELECT * FROM Student LEFT JOIN SC ON (Student.Sno=SC.Sno);

11、嵌套查询

/*去掉Student.Cname的UNIQUE*/
ALTER TABLE Student DROP INDEX Sname;
/*带有比较运算符的子查询*/
SELECT Sno,Sname,Sdept
FROM Student
WHERE Sdept = (
    SELECT Sdept
    FROM Student
    WHERE Sno='20071004');
                         
SELECT Sno,Sname,Sdept
FROM Student
WHERE Sno IN (
    SELECT Sno
    FROM SC
    WHERE Grade>=5);
                         
/*带有ANY(SOME)或ALL谓词的子查询*/                          
SELECT Sno,Sname,Sage,Ssex
FROM Student
WHERE Sage>ANY (
    SELECT Sage
    FROM Student
    WHERE Ssex='fe');
/*带有[NOT] EXISTS谓词的子查询*/
/*EXISTS谓词的子查询不反悔任何数据，只产生逻辑真与假*/
/*拿外层的元组逐个放在内层中判断是否EXIST，如果为真则将元组放入结果集*/
SELECT Sname
FROM Student
WHERE EXISTS (
    SELECT *
    FROM SC
    WHERE Sno=Student.Sno
    AND Cno='100');
                             
/*集合查询：UNION并集，INTERSECT交集，EXCEPT差集*/
SELECT Sno
FROM Student
WHERE Sdept='hwx'
UNION
SELECT *
FROM Student
WHERE Sage>=20;

12、视图操作

/*创建视图*/
CREATE VIEW V_Student
AS
SELECT Sno,Sname,Sage
FROM Student
WHERE Sdept='xj';
/*删除视图*/
DROP VIEW V_Student;
/*查询视图*/
SELECT Sno,Sname
FROM V_Student
WHERE Sage>50;
/*更新视图*/
UPDATE V_Student
SET Sname='vname'
WHERE Sno='20071089';
INSERT INTO V_Student
VALUES ('20081010','vnew',36);

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