DB sql每日练习

Mysql每日训练

创建表以及插入联系数据

---建表
---学生表
CREATE TABLE `Student`(
    `s_id` VARCHAR(20),
    `s_name` VARCHAR(20) NOT NULL DEFAULT '',
    `s_birth` VARCHAR(20) NOT NULL DEFAULT '',
    `s_sex` VARCHAR(10) NOT NULL DEFAULT '',
    PRIMARY KEY(`s_id`)
);
--课程表
CREATE TABLE `Course`(
    `c_id`  VARCHAR(20),
    `c_name` VARCHAR(20) NOT NULL DEFAULT '',
    `t_id` VARCHAR(20) NOT NULL,
    PRIMARY KEY(`c_id`)
);
--教师表
CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20) NOT NULL DEFAULT '',
    PRIMARY KEY(`t_id`)
);
--成绩表
CREATE TABLE `Score`(
    `s_id` VARCHAR(20),
    `c_id`  VARCHAR(20),
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
);
--插入学生表测试数据
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
--课程表测试数据
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

--教师表测试数据
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

--成绩表测试数据
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);

根据问题进行查询

– 1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
SELECT a.*,b.s_score AS 01_score,c.s_score AS 02_score FROM
student a JOIN score b ON a.s_id = b.s_id AND b.c_id=‘01’ – 连接学生和分数表查询到01号课程的成绩
LEFT JOIN – 左加入到分数表，进行条件过滤
score c
ON a.s_id=c.s_id AND c.c_id=‘02’ or c.c_id= NULL
WHERE c.s_score < b.s_score

– 2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
SELECT a.*, b.s_score as 02_score, b.s_score as 01_score FROM
student a JOIN score b ON a.s_id = b.s_id AND b.c_id=‘02’
LEFT JOIN
score c
ON a.s_id=c.s_id AND c.c_id=‘01’ OR c.c_id =NULL
WHERE b.s_score > c.s_score

– 3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
SELECT a.s_id,a.s_name,(b.s_score) as average_score FROM
student a JOIN score b ON a.s_id = b.s_id
GROUP BY a.s_id
HAVING average_score >= 60
ORDER BY average_score

– 4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩-- (包括有成绩的和无成绩的)
SELECT a.s_id,a.s_name,(b.s_score) as average_score FROM
student a LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY a.s_id
HAVING average_score < 60

– 5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
SELECT a.s_id,a.s_name,COUNT(a.s_id) as count_class ,SUM(b.s_score) as sum_score FROM
student a LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY a.s_id

-----------------------------------9.24更-------------------------------

– 6、查询"李"姓老师的数量
SELECT COUNT(*) as named_li FROM
teacher
WHERE teacher.t_name LIKE ‘李%’

– 7、查询学过"张三"老师授课的同学的信息
SELECT st1.,t1. FROM
student st1 LEFT JOIN score sc1
ON st1.s_id = sc1.s_id
LEFT JOIN
teacher t1
ON sc1.c_id = t1.t_id
WHERE t1.t_name LIKE ‘张三’

– 8、查询没学过"张三"老师授课的同学的信息
SELECT st1.,t1. FROM
student st1 LEFT JOIN score sc1
ON st1.s_id = sc1.s_id
LEFT JOIN
teacher t1
ON sc1.c_id = t1.t_id
WHERE t1.t_name NOT LIKE ‘张三’

– 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
select a.* from
student a,score b,score c
where a.s_id = b.s_id and a.s_id = c.s_id and b.c_id=‘01’ and c.c_id=‘02’;

– 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
select a.* from
student a
where a.s_id in (select s_id from score where c_id=‘01’ ) and a.s_id not in(select s_id from score where c_id=‘02’)