SQL常用命令集1

 最近在学习数据库理论，顺便把SQL学习一下，下面列出常用的SQL命令 （全部在MySQL上测试通过）。

 

1.  创建表 

CREATE TABLE Student (Sno CHAR(5) NOT NULL UNIQUE, Sname CHAR(20), Ssex CHAR(2), Sage INT, Sdept CHAR(15));
CREATE TABLE course(Cno CHAR(5) NOT NULL UNIQUE, Cname CHAR(30), Cpno CHAR(5), Ccredit SMALLINT);
CREATE TABLE SC(Sno char(5) NOT NULL, Cno char(5) NOT NULL, Grade SMALLINT NOT NULL);

  

 

1.5 增加外键

mysql> ALTER TABLE course ADD CONSTRAINT fk_pno
    -> FOREIGN KEY (Cpno)
    -> REFERENCES course(Cno);

mysql> ALTER TABLE sc ADD CONSTRAINT fk_sno
    -> FOREIGN KEY(Sno)
    -> REFERENCES student(Sno);

mysql> ALTER TABLE sc ADD CONSTRAINT fk_cno
    -> FOREIGN KEY(Cno)
    -> REFERENCES Course(Cno);

 

2.  改变表 

ALTER TABLE Student ADD Scome DATE; 
ALTER TABLE Student MODIFY Sage SMALLINT;

  

3. 删除表

DROP TABLE Student

 

4. 插入信息

INSERT INTO Student VALUES ("95001", "李勇", "男", 20, "CS");
INSERT INTO Student VALUES ("95002", "刘晨", "女", 19, "IS");
INSERT INTO Student VALUES ("95003", "王名", "女", 18, "MA");
INSERT INTO Student VALUES ("95004", "张立", "男", 19, "IS");

INSERT INTO course VALUES ("6", "数据处理", NULL, 2);
INSERT INTO courses VALUES ("2", "数学", NULL, 2);
INSERT INTO course VALUES ("7", "PASCAL语言", "6", 4);
INSERT INTO course VALUES ("4", "操作系统", "6", 3);
INSERT INTO course VALUES ("5", "数据结构", "7", 3);
INSERT INTO course VALUES ("1", "数据库", "5", 4);
INSERT INTO course VALUES ("3", "信息系统", "1", 4);

INSERT INTO sc VALUES("95001", "1", 92);
INSERT INTO sc VALUES("95001", "2", 85);
INSERT INTO sc VALUES("95001", "3", 88);
INSERT INTO sc VALUES("95002", "2", 90);
INSERT INTO sc VALUES("95002", "3", 80);

  

5. 建立索引

CREATE UNIQUE INDEX Stusno ON Student(Sno);
CREATE UNIQUE INDEX Coucno ON course(Cno);
CREATE UNIQUE INDEX SCno ON SC(Sno ASC, Cno DESC);

  

6. 删除索引

DROP INDEX Stusno on Student;

  

7. 查询

　7.1 单表查询

　　7.1.1 对列

select Sno, Sname from student;
select Sno, 2009-Sage from student;
select * from student;
select Sname NAME, 'Year of Birth:' BIRTH, 2009-Sage BIRTHDAY, LOWER(Sdept) DEPARTMENT from student;

　　7.1.2 对行

select Sname from student where Sdept='CS';
select Sname, Sage from student where Sage<20;
select * from SC where grade>85;
select Sname, Sdept, Sage from student where Sage between 20 and 23;
select Sname, Ssex from student where Sdept not in ('CS', 'MA');
select * from student where Sname like '刘%';
select * from course where Cpno is NULL;
select Sname, Ssex from student where Sdept='IS' and Sage=19;

　　7.1.3 排序

　select * from student Order by Sdept, Sage DESC;

　　7.1.4 使用函数

　select COUNT(*) from student;
　select COUNT(DISTINCT Sno) from SC;
　select AVG(GRADE) from SC where Cno='1';
　select MAX(GRADE) from SC where Cno='2';

 　　7.1.5 对查询结果分组

　select Cno, COUNT(Sno) from SC Group by Cno;
　select Cno, COUNT(Sno) from SC Group by Cno having COUNT(*) <2;   

 

   7.2 连接查询

 　　7.2.1 等值非等值查询

select student.*, SC.* from student, sc where student.Sno=sc.Sno;

 　　7.2.2 自身连接

select first.Cno, Second.Cpno from course first, course second where first.Cpno=second.Cno and second.Cpno is not null;

 　　7.2.3 外连接

select Student.Sno, Sname, Ssex, Sage, Sdept, Cno, Grade from Student left join sc on sc.Sno=student.Sno;

 

    7.3 复合条件连接

select Student.Sno, Sname,Cname, Grade from student, course, sc where sc.Sno=Student.Sno AND sc.Cno=Course.Cno;