做了一些mysql的习题 感觉用来应付面试是足够了
1.创建student和score表
CREATE TABLE student (
id INT(10) NOT NULL UNIQUE PRIMARY KEY ,
name VARCHAR(20) NOT NULL ,
sex VARCHAR(4) ,
birth YEAR,
department VARCHAR(20) ,
address VARCHAR(50)
);
创建score表。SQL代码如下：
CREATE TABLE score (
id INT(10) NOT NULL UNIQUE PRIMARY KEY AUTO_INCREMENT ,
stu_id INT(10) NOT NULL ,
c_name VARCHAR(20) ,
grade INT(10)
);
2.为student表和score表增加记录
向student表插入记录的INSERT语句如下：
INSERT INTO student VALUES( 901,'张老大', '男',1985,'计算机系', '北京市海淀区');
INSERT INTO student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
INSERT INTO student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
INSERT INTO student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
INSERT INTO student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
INSERT INTO student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');
向score表插入记录的INSERT语句如下：
INSERT INTO score VALUES(NULL,901, '计算机',98);
INSERT INTO score VALUES(NULL,901, '英语', 80);
INSERT INTO score VALUES(NULL,902, '计算机',65);
INSERT INTO score VALUES(NULL,902, '中文',88);
INSERT INTO score VALUES(NULL,903, '中文',95);
INSERT INTO score VALUES(NULL,904, '计算机',70);
INSERT INTO score VALUES(NULL,904, '英语',92);
INSERT INTO score VALUES(NULL,905, '英语',94);
INSERT INTO score VALUES(NULL,906, '计算机',90);
INSERT INTO score VALUES(NULL,906, '英语',85);
下面是习题的答案 感觉还是有所收获的
3.查询student表的所有记录
select * from student
4.查询student表的第2条到4条记录
select * from student limit 1,3
5.从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息
select id ,name ,department from student
6.从student表中查询计算机系和英语系的学生的信息
select * from student where department in ('计算机系','英语系')
从student表中查询年龄18~22岁的学生信息
select * from student where 2017-birth BETWEEN 18 and 30
从student表中查询每个院系有多少人
select department,count(1) from student GROUP BY department
从score表中查询每个科目的最高分
select c_name,MAX(grade) from score GROUP BY c_name
查询李四的考试科目（c_name）和考试成绩（grade）
select t1.c_name,t1.grade from score t1 left join student t2 on t1.stu_id = t2.id where t2.name = '李四'
select t1.c_name ,t1.grade from score t1 where t1.stu_id =(select id from student where name='李四')
select t1.c_name ,t1.grade from score t1,student t2 where t2.name = '李四' and t1.stu_id = t2.id
用连接的方式查询所有学生的信息和考试信息
select student.id,name,sex,birth,department,address,c_name,grade from score,student where score.stu_id = student.id
计算每个学生的总成绩
select t2.name,sum(t1.grade) from score t1,student t2 WHERE t1.stu_id = t2.id GROUP BY t2.name
13.计算每个考试科目的平均成绩
select c_name, AVG(grade)from score GROUP BY c_name
14.查询计算机成绩低于95的学生信息
select t1.name,t1.sex,t1.birth,t1.department,t1.address,t2.grade,t2.c_name from student t1 ,score t2 where t2.c_name='计算机' and t2.grade<95 and t1.id = t2.stu_id
15.查询同时参加计算机和英语考试的学生的信息
select t1.name,t1.sex,t1.birth,t1.department,t1.address from student t1,score t2,score t3
where t1.id = t2.stu_id
and t2.c_name ='计算机'
and t1.id = t3.stu_id
and t3.c_name='英语'
SELECT * FROM student
WHERE id =ANY
(SELECT stu_id FROM score WHERE stu_id IN( SELECT stu_id FROM score WHERE c_name= '计算机') AND c_name= '英语')
16.将计算机考试成绩按从高到低进行排序
select * from score where c_name='计算机' order by grade desc
17.从student表和score表中查询出学生的学号，然后合并查询结果
SELECT id FROM student
UNION
SELECT stu_id FROM score;
18.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩
select t1.name,t1.sex,t1.birth,t1.department,t1.address,t2.grade,t2.c_name from student t1 ,score t2 where
(t1.name like '张%' or t1.name like '王%')
and t1.id = t2.stu_id
19.查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩
select t1.name,t1.sex,t1.birth,t1.department,t1.address,t2.grade,t2.c_name from student t1 ,score t2 where
t1.address like '湖南%'
and t1.id = t2.stu_id
合并着查询的效率比子查询的效率高多了
