MySql基础--灵活运用sql语句

数据库脚本

• 请勿随意修改本人数据，内藏玄机。可随意增加数据
• 补充：DISTINCT：去重

-- 1. 创建学生表
CREATE TABLE t_student (
	sid INT NOT NULL AUTO_INCREMENT COMMENT '学号',
	sname VARCHAR(40) NOT NULL COMMENT '名称',
	birthday DATE NOT NULL COMMENT '年龄',
	ssex TINYINT NOT NULL DEFAULT 1 COMMENT '1男，2女',
	PRIMARY KEY (sid)
);
-- 添加数据
INSERT INTO t_student VALUES(1, '赵雷' , '1990-01-01' , 1);
INSERT INTO t_student VALUES(2 , '钱电' , '1990-12-21' , 1);
INSERT INTO t_student VALUES(3 , '孙风' , '1990-12-20' , 1);
INSERT INTO t_student VALUES(4 , '李云' , '1990-12-06' , 1);
INSERT INTO t_student VALUES(5 , '周梅' , '1991-12-01' , 2);
INSERT INTO t_student VALUES(6 , '吴兰' , '1992-01-01' , 2);
INSERT INTO t_student VALUES(7 , '郑竹' , '1989-01-01' , 2);
INSERT INTO t_student VALUES(9 , '张三' , '2017-12-20' , 2);
INSERT INTO t_student VALUES(10 , '李四' , '2017-12-25' , 2);
INSERT INTO t_student VALUES(11 , '李四' , '2012-06-06' , 2);
INSERT INTO t_student VALUES(12 , '赵六' , '2013-06-13' , 2);
INSERT INTO t_student VALUES(13 , '孙七' , '2014-06-01' , 2);
-- 2.创建教师表
CREATE TABLE t_teacher (
	tid INT NOT NULL AUTO_INCREMENT COMMENT '教师ID',
	tname VARCHAR(40) NOT NULL COMMENT '教师名称',
	PRIMARY KEY (tid)
);
-- 添加收据
INSERT INTO t_teacher VALUES(1 , '张五哥');
INSERT INTO t_teacher VALUES(2 , '李卫');
INSERT INTO t_teacher VALUES(3 , '年羹尧');
-- 3.课程表
CREATE TABLE t_course (
	cid INT NOT NULL COMMENT '课程ID',
	cname VARCHAR(50) COMMENT '课程名称',
	tid INT COMMENT '教师id',
	PRIMARY KEY (cid)
);
-- 添加数据
INSERT INTO t_course VALUES(1 , '语文' , 2);
INSERT INTO t_course VALUES(2 , '数学' , 1);
INSERT INTO t_course VALUES(3 , '英语' , 3);

-- 4.成绩表
CREATE TABLE t_score (
	sid INT NOT NULL COMMENT '学号，外键',
	cid INT NOT NULL COMMENT '课程id',
	score decimal(5,2) COMMENT '成绩',
	UNIQUE KEY ak_key_sid_cid (sid, cid)
);

-- 添加数据
INSERT INTO t_score VALUES(1 , 1 , 80);
INSERT INTO t_score VALUES(1 , 2 , 90);
INSERT INTO t_score VALUES(1 , 3 , 99);
INSERT INTO t_score VALUES(2 , 1 , 70);
INSERT INTO t_score VALUES(2 , 2 , 60);
INSERT INTO t_score VALUES(2 , 3 , 80);
INSERT INTO t_score VALUES(3 , 1 , 80);
INSERT INTO t_score VALUES(3 , 2 , 80);
INSERT INTO t_score VALUES(3 , 3 , 80);
INSERT INTO t_score VALUES(4 , 1 , 50);
INSERT INTO t_score VALUES(4 , 2 , 30);
INSERT INTO t_score VALUES(4 , 3 , 20);
INSERT INTO t_score VALUES(5 , 1 , 76);
INSERT INTO t_score VALUES(5 , 2 , 87);
INSERT INTO t_score VALUES(6 , 1 , 31);
INSERT INTO t_score VALUES(6 , 3 , 34);
INSERT INTO t_score VALUES(7 , 2 , 89);
INSERT INTO t_score VALUES(7 , 3 , 98);

题目：

01）查询" 1 "课程比" 2 "课程成绩高的学生的信息及课程分数
select * from t_student stu
INNER JOIN
(select c1.sid,c1.cid i1,c1.score s1,c2.cid i2 ,c2.score s2 from 
(select * from t_score where cid =1)c1
INNER JOIN
(select * from t_score where cid =2) c2
on c1.sid=c2.sid) cc
on cc.sid = stu.sid
02）查询同时存在" 01 "课程和" 02 "课程的情况
select * from t_student stu 
INNER JOIN
(select c1.sid ,c1.cid c1id,c2.cid c2cid  from 
(select * from t_score where cid =1) c1
INNER JOIN
(select * from t_score where cid =2) c2
on c1.sid=c2.sid) cc
on cc.sid=stu.sid
03）查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
select 
	t.sid, 
	sum(case when t.cid=1 then t.score else 0 end), 
	sum(case when t.cid=2 then t.score else null end) 
	from t_score t GROUP BY t.sid
 
04）查询不存在" 01 "课程但存在" 02 "课程的情况
select t.sid,
	sum(case when t.cid=1 then t.score else null end ),
	sum(case when t.cid=2 then t.score else 0 end )
from t_score t GROUP BY t.sid

05）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 aa.sid,st.*,aa.s1 from t_student st
INNER JOIN
(select * from (
select sid,avg(score) s1 from t_score GROUP BY sid 
) t where t.s1 >= 60) aa
on aa.sid=st.sid

06）查询在t_score表存在成绩的学生信息
select * from t_student t where exists (select * from t_score ts where ts.sid=t.sid)

select DISTINCT stu.sid,stu.sname,stu.birthday from t_score t INNER JOIN (select * from t_student) stu on t.sid=stu.sid  

07）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(没成绩的显示为 null )
select sid,asname,ccid,count(score) from 
(
select * from 
(select * from 
(select sid asid,sname asname from t_student) a
INNER JOIN
(select sid bsid,count(cid) ccid from t_score GROUP BY sid) b
on a.asid=b.bsid
) c
INNER JOIN
(select * from t_score) d
on c.asid=d.sid
)  e GROUP BY sid 

08）查询「李」姓老师的数量
select count(tid) from t_teacher where tname like '李%';

09）查询学过「张三」老师授课的同学的信息
select * from t_student c
INNER JOIN
(select a.sid from 
(select * from t_score) a
INNER JOIN 
(select tid from t_teacher where tname like '李卫') b
on a.cid=b.tid) d
on d.sid=c.sid

10）查询没有学全所有课程的同学的信息
  SELECT t1.`sid`,t1.`sname`,t1.`ssex`, t2.courses 
    FROM t_student t1 
    LEFT JOIN (SELECT sid,COUNT(*) courses FROM t_score GROUP BY sid) t2 ON t1.sid = t2.sid
  WHERE t2.courses < (SELECT COUNT(*) FROM t_course) OR t2.courses IS NULL;
11）查询没学过"张三"老师讲授的任一门课程的学生姓名
select distinct stu.sname from t_student stu
INNER JOIN
(select * from t_score t
INNER JOIN
(select tid from t_teacher where tname !='李卫') tt
on t.cid=tt.tid
) ss
on stu.sid=ss.sid

12）查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
SELECT t3.sid, t3.sname, ROUND(AVG(t1.score), 2) scoreavg
  FROM t_score t1
       INNER JOIN (
          -- 统计两门以上不及格的学生id
          SELECT t.sid, COUNT(*) num FROM (SELECT sid, cid FROM t_score WHERE score < 60) t GROUP BY t.sid HAVING num >= 2
       ) t2 ON t1.sid = t2.sid 
       INNER JOIN t_student t3 ON t1.sid = t3.sid
 GROUP BY t3.sid, t3.sname
13）检索" 01 "课程分数小于 60，按分数降序排列的学生信息
SELECT t1.`sid`,t1.`sname`,t3.score
  FROM t_student t1 
       INNER JOIN (SELECT sid,score FROM t_score WHERE cid = 1 AND score < 60) t3
       ON t1.`sid` = t3.sid
  ORDER BY t3.score DESC;
14）按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
SELECT 	t2.sid,t2.sname , 
	SUM(CASE WHEN t1.cid = 1 THEN t1.score ELSE 0 END) '语文',
	SUM(CASE WHEN t1.cid = 2 THEN t1.score ELSE 0 END) '数学',
	SUM(CASE WHEN t1.cid = 3 THEN t1.score ELSE 0 END) '英语',
	ROUND(AVG(t1.`score`), 2) avgscore
FROM t_score t1 
     INNER JOIN t_student t2 ON t1.sid = t2.sid
 GROUP BY t2.sid, t2.sname
 ORDER BY avgscore DESC;
15）查询各科成绩最高分、最低分和平均分：
SELECT t2.cid '课程ID', 
       t2.cname '课程名称',
       MAX(t1.score) '最高分',
       MIN(t1.score) '最低分',
       ROUND(AVG(t1.score), 2) '平均分',
       COUNT(t1.sid) '选修人数',
       ROUND(SUM(CASE WHEN t1.score >= 60 THEN 1 ELSE 0 END) / COUNT(t1.sid), 2) '及格率',
       ROUND(SUM(CASE WHEN t1.score >=70 AND t1.score < 80 THEN 1 ELSE 0 END)/COUNT(t1.sid),2) '中等率',
       ROUND(SUM(CASE WHEN t1.score >=80 AND t1.score < 90 THEN 1 ELSE 0 END)/COUNT(t1.sid),2) '优良率',
       ROUND(SUM(CASE WHEN t1.score >= 90 THEN 1 ELSE 0 END)/COUNT(t1.sid), 2) '优秀率'
 FROM t_score t1
      INNER JOIN t_course t2 ON t1.cid = t2.cid
  GROUP BY t2.cid, t2.cname
  ORDER BY COUNT(t1.sid) DESC, t2.cid ASC;

以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90

要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

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