实践：
总结：
学生分数，总和，降序排列。
SELECT id,stname,math+english+chiniese AS ss FROM score ORDER BY ss DESC;
查询平均成绩大于60分的同学的学号和平均成绩。（后两者可行，前一个是我随意写的。）
SELECT stuid FROM score WHERE cid=1;
SELECT stuid,SUM(s)/3 AS ss FROM score WHERE stuid=1;
SELECT stuid,AVG(s) FROM score GROUP BY stuid HAVING AVG(s)>10;
查询所有同学的学号、姓名、选课数、总成绩。
SELECT student.stuid,student.stuname,COUNT(score.cid),SUM(score.s) FROM Student LEFT OUTER JOIN score ON student.stuid=score.stuid GROUP BY Student.stuid, Student.stuname;
题目1：
源代码：
执行：select语句变成如下：
源代码：
CREATE DATABASE t_table;
CREATE TABLE score(
id INT PRIMARY KEY AUTO_INCREMENT,
stname VARCHAR(10) NOT NULL,
math INT,
english INT,
chiniese INT
)CHARSET utf8;
INSERT INTO score(id,stname,math,english,chiniese) VALUES
(1,'xiaoming',7,5,6),
(3,'cai',7,5,6),
(2,'hong',5,2,3)
SELECT id,stname,math+english+chiniese AS ss FROM score ORDER BY ss DESC;
题目2：
源代码：
CREATE DATABASE test;
CREATE TABLE student(
stuid INT PRIMARY KEY AUTO_INCREMENT,
stuname VARCHAR(20),
age INT,
gender VARCHAR(20)
)
CREATE TABLE course(
cid INT PRIMARY KEY AUTO_INCREMENT,
cname VARCHAR(20),
tid INT
)
CREATE TABLE score(
stuid INT,
cid INT,
s INT
)
INSERT INTO student(stuid,stuname,age,gender)VALUES //学生
(1,'ming',18,'girl'),
(2,'hong',19,'boy'),
(3,'king',10,'boy'),
(4,'ging',13,'girl');
INSERT INTO course(cid,cname,tid)VALUES //课程
(1,'english',1),
(2,'chiniese',2),
(3,'math',3);
INSERT INTO score(stuid,cid,s)VALUES //分数
(1,1,90),
(1,3,30),
(1,2,50),
(4,2,99),
(3,1,44);
查询平均成绩大于60分的同学的学号和平均成绩。
SELECT stuid FROM score WHERE cid=1;
SELECT stuid,SUM(s)/3 AS ss FROM score WHERE stuid=1;
SELECT stuid,AVG(s) FROM score GROUP BY stuid HAVING AVG(s)>10;
查询所有同学的学号、姓名、选课数、总成绩。
SELECT student.stuid,student.stuname,COUNT(score.cid),SUM(score.s) FROM Student LEFT OUTER JOIN score ON student.stuid=score.stuid GROUP BY Student.stuid, Student.stuname;
