MySQL入门学习(1)：

服务开启与关闭：

开启MySQL服务:NET SATRT [MySQL服务名]

关闭MySQL服务：NET START 【MySQL服务名]

例如：NET START MYSQL56_1

NET STOP MYSQL56_1

查询已开启的服务；NET START

创建表：

例如：

(1) 建立教学管理中的三个基本表：

Students（S＃，SNAME，AGE，SEX）学生（学号，姓名，年龄，性别）

Courses（C＃，CNAME，SCORE，PC＃）课程（课程号，课程名，学分，先行课号）

SC（S＃，C#，GRADE）选修（学号，课程号，成绩）

mysql> Create table Students(
    -> SN CHAR(5),
    -> SNAME CHAR(20) NOT NULL,
    -> AGE INT,
    -> SEX CHAR(2),
    -> primary key(SN));
Query OK, 0 rows affected (0.03 sec)

mysql> Create table Courses(
    -> CN CHAR(5),
    -> CNAME CHAR(20) NOT NULL,
    -> Score float,
    -> PCN CHAR(2),
    -> primary key(CN));
Query OK, 0 rows affected (0.07 sec)

mysql> Create table SC(
    -> SN CHAR(5),
    -> CN CHAR(5),
    -> GRADE FLOAT,
    -> PRIMARY KEY(SN,CN));
Query OK, 0 rows affected (0.08 sec)

添加数据：

（1）用INSERT 命令输入数据。

表6 基本表Students的数据：

表7基本表Courses的数据

表8 基本表SC的数据（空格为未选修）：

mysql> insert into students values('S1','LU',20,'M');
Query OK, 1 row affected (0.04 sec)

mysql> insert into students values('S2','YIN',19,'M');
Query OK, 1 row affected (0.06 sec)

mysql> insert into students values('S3','XU',18,'F');
Query OK, 1 row affected (0.05 sec)

mysql> insert into students values('S4','QU',18,'F');
Query OK, 1 row affected (0.00 sec)

mysql> insert into students values('S6','PAN',14,'M');
Query OK, 1 row affected (0.05 sec)

mysql> insert into students values('S8','DONG',24,'M');
Query OK, 1 row affected (0.05 sec)

mysql> INSERT INTO COURSES VALUES('C1','数学',4,'M');
Query OK, 1 row affected (0.07 sec)

mysql> INSERT INTO COURSES VALUES('C2','英语',8,'M');
Query OK, 1 row affected (0.06 sec)

mysql> INSERT INTO COURSES VALUES('C3','数据结构',4,'F');
Query OK, 1 row affected (0.06 sec)

mysql> INSERT INTO COURSES VALUES('C4','数据库',3.5,'F');
Query OK, 1 row affected (0.07 sec)

mysql> INSERT INTO COURSES VALUES('C5','网络',4,'M');
Query OK, 1 row affected (0.06 sec)

mysql> insert into sc values('S1','C1',85);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO SC VALUES('S1','C2',73);
Query OK, 1 row affected (0.01 sec)

mysql> insert into sc values('S1','C4',89);
Query OK, 1 row affected (0.00 sec)

mysql> insert into sc values('S1','C5',73);
Query OK, 1 row affected (0.00 sec)

mysql> insert into sc values('S2','C1',90);
Query OK, 1 row affected (0.01 sec)

mysql> insert into sc values('S2','C3',80);
Query OK, 1 row affected (0.01 sec)

mysql> insert into sc values('S2','C4',85);
Query OK, 1 row affected (0.15 sec)

mysql> insert into sc values('S3','C1',89);
Query OK, 1 row affected (0.00 sec)

mysql> insert into sc values('S3','C2',86);
Query OK, 1 row affected (0.10 sec)

mysql> insert into sc values('S4','C1',84);
Query OK, 1 row affected (0.10 sec)

mysql> insert into sc values('S4','C2',82);
Query OK, 1 row affected (0.00 sec)

………………………..

数据查询

( 1 ) 列出选修课程号为C2的学生学号与姓名。

（2）检索选修课程名为“数学”的学生学号与姓名。

（3）检索没有选修C2课程的学生姓名与年龄。

（4）检索选修全部课程的学生姓名。

mysql> selECT STUDENTS.SN,STUDENTS.SNAME FROM STUDENTS,SC
    -> WHERE (STUDENTS.SN=SC.SN) AND (SC.CN='C2');
+----+-------+
| SN | SNAME |
+----+-------+
| S1 | LU    |
| S3 | XU    |
| S4 | QU    |
| S6 | PAN   |
| S8 | DONG |
+----+-------+
5 rows in set (0.09 sec)

mysql> selECT STUDENTS.SN,STUDENTS.SNAME FROM STUDENTS,COURSES,SC
-> WHERE (STUDENTS.SN=SC.SN) AND (SC.CN=COURSES.CN) AND (COURSES.CNAME='网络');
+----+-------+
| SN | SNAME |
+----+-------+
| S1 | LU |
| S8 | DONG |
+----+-------+
2 rows in set (0.00 sec)

mysql> select students.SNAME,students.age
    -> from students,sc
    -> where students.sn=sc.sn and sc.cn='C2' and sc.grade IS NULL;
+-------+------+
| SNAME | age |
+-------+------+
| YIN   |   19 |
+-------+------+
1 row in set (0.00 sec)

mysql> delete
    -> from sc
    -> where Grade is NULL;
Query OK, 10 rows affected (0.03 sec)

mysql> select SNAME
    -> from students
    -> where not exists
    -> (Select * from courses
    -> where not exists
    -> (select * from sc
    -> where sc.sn=students.sn and sc.cn=courses.cn));
+-------+
| SNAME |
+-------+
| LU    |
+-------+
1 row in set (0.00 sec)

数据修改、删除

（1）           把C2课程的非空成绩提高10％。

（2）           在SC表中删除课程名为“物理”的成绩所对应的元组。

（3）           在S和SC表中删除学号为S8的所有数据。

mysql> update sc
-> set grade=grade*1.1
-> where cn='C2';
Query OK, 5 rows affected (0.07 sec)
Rows matched: 5 Changed: 5 Warnings: 0

mysql> select * from sc
-> where cn='C2';
+----+----+-------+
| SN | CN | GRADE |
+----+----+-------+
| S1 | C2 | 80.3 |
| S3 | C2 | 94.6 |
| S4 | C2 | 90.2 |
| S6 | C2 | 82.5 |
| S8 | C2 | 93.5 |
+----+----+-------+
5 rows in set (0.00 sec)

mysql> delete
-> from sc
-> where cn=(select cn
-> from courses
-> where cname='物理');
Query OK, 0 rows affected (0.00 sec)

mysql> delete from sc
-> where sc.sn='S8';
Query OK, 4 rows affected (0.05 sec)

mysql> delete from students where sn='S8';
Query OK, 1 row affected (0.00 sec)

视图的操作

（1）       建立男生学生的视图，属性包括学号，姓名，选修课程名和成绩。

（2）       在男生视图中查询平均成绩大于80分的学生学号和姓名。

mysql> create view M
-> as
-> select students.sn,sname,cname,grade
-> from students,courses,sc
-> where students.sn=sc.sn and courses.cn=sc.cn;
Query OK, 0 rows affected (0.06 sec)

mysql> select sn,sname
-> from M
-> where AVG(grade)>80
-> group by sn;
ERROR 1111 (HY000): Invalid use of group function

此处WHERE子句不能使用聚集函数作为表达式作为条件表达式，因此执行此查询将会出现语法错误。

mysql> select sn,sname
-> from M
-> group by sn
-> HAVING AVG(grade)>80;
+----+-------+
| sn | sname |
+----+-------+
| S1 | LU |
| S2 | YIN |
| S3 | XU |
| S4 | QU |
| S6 | PAN |
+----+-------+
5 rows in set (0.00 sec)