Sql语句50条案例，从创建数据库入门到进阶

#### Sql语句50条案例demo 一. 提示: 根据文章: (https://zhuanlan.zhihu.com/p/43289968) 和<br> (https://zhuanlan.zhihu.com/p/38354000) 完成; 表结构关系: <div align="left"> <img width="500px" height="280px" src="https://pic1.zhimg.com/80/v2-86fd263583a6cead51675982c1735e68_hd.jpg" /> </div> 二. 建表语句: ``` /*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`) ); ``` 插入数据: ``` /*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); ``` 三. 练习案例: 1、查询课程编号为“01”的课程比“02”的课程成绩高的所有学生的学号 > 三个表连接，s_score分为两列: ``` SELECT st.*, a.s_score, b.s_score FROM student st INNER JOIN (SELECT s_id, s_score FROM Score WHERE c_id='01') a ON st.s_id=a.s_id INNER JOIN (SELECT s_id, s_score FROM Score WHERE c_id='02') b ON a.s_id=b.s_id WHERE a.s_score > b.s_score; ``` <br> 2、查询平均成绩大于60分的学生的学号和平均成绩 ``` SELECT s_id, AVG(s_score) FROM Score GROUP BY s_id HAVING AVG(s_score) > 60; ``` <br> 3、查询所有学生的学号、姓名、选课数、总成绩 ``` SELECT A.s_id, A.s_name, COUNT(B.c_id) AS 选课数, SUM(B.s_score) AS 总成绩 FROM student A JOIN score B ON A.s_id=B.s_id GROUP BY A.s_id, A.s_name; ``` <br> 4、查询姓“猴”的老师的个数 ``` SELECT COUNT(t_id) From teacher where t_name like '猴%'; ``` <br> 5、查询没学过“张三”老师课的学生的学号、姓名 ``` SELECT * FROM Student WHERE s_id NOT IN (SELECT sc.s_id FROM Score sc INNER JOIN Course co ON sc.c_id=co.c_id INNER JOIN Teacher te ON co.t_id=te.t_id WHERE te.t_name='张三'); ``` <br> 6、查询学过“张三”老师所教的所有课的同学的学号、姓名 ``` SELECT * FROM Student WHERE s_id IN (SELECT sc.s_id FROM Score sc INNER JOIN Course co ON sc.c_id=co.c_id INNER JOIN Teacher te ON co.t_id=te.t_id WHERE te.t_name='张三'); ``` <br> 7、查询学过编号为“01”的课程并且也学过编号为“02”的课程的学生的学号、姓名 ``` SELECT * FROM student where s_id IN (SELECT a.s_id FROM (SELECT * FROM Score WHERE c_id='01') a INNER JOIN (SELECT * FROM Score WHERE c_id='02') b ON a.s_id=b.s_id); ``` <br> 8、查询学过编号为“01”的课程, 但没学过编号为“02”的课程的学生的学号、姓名 ``` SELECT * FROM student WHERE s_id IN (SELECT s_id FROM Score WHERE c_id='01') AND s_id NOT IN (SELECT s_id FROM Score WHERE c_id='02'); ``` <br> 9、查询课程编号为“02”的总成绩 ``` SELECT SUM(s_score) FROM Score WHERE c_id='02'; /*或*/ SELECT c_id, SUM(s_score) FROM score GROUP BY c_id HAVING c_id = '02'; ``` <br> 10、查询所有课程成绩小于60分(全部课程不及格)的学生的学号、姓名 ``` /*1.得出同学课程成绩小于60分的课程数*/ /*2.统计同学总共学了几门课程*/ /*3.如果相等就是全部课程不及格*/ SELECT a.s_id, t.s_name FROM (SELECT s_id, COUNT(c_id) AS cnt FROM score WHERE s_score<60 GROUP BY s_id) a INNER JOIN (SELECT s_id, COUNT(c_id) AS cnt FROM score GROUP BY s_id) b ON a.s_id=b.s_id INNER JOIN student t ON a.s_id=t.s_id WHERE a.cnt=b.cnt; /*另一种简便方法,如果最大成绩都小于60,那么这个同学所有课程不及格*/ SELECT s_id, s_name FROM student WHERE s_id IN (SELECT s_id FROM score GROUP BY s_id HAVING MAX(s_score)<60); ``` <br> 11.查询没有学全所有课的学生的学号、姓名 ``` SELECT st.*, sc.* FROM student AS st LEFT JOIN score AS sc ON st.s_id=sc.s_id GROUP BY st.s_id HAVING COUNT(DISTINCT sc.c_id) < (SELECT COUNT(DISTINCT c_id) FROM course); ``` <br> 12、查询至少有一门课与学号为“01”的学生所学课程相同的学生的学号和姓名 ``` SELECT DISTINCT st.* FROM student st INNER JOIN score sc ON st.s_id=sc.s_id WHERE sc.c_id IN (SELECT c_id FROM score WHERE s_id='01') AND st.s_id != '01'; ``` 13.查询和“01”号同学所学课程完全相同的其他同学的学号 ``` /*第一步是查出和01号同学(不包括自己)所学课程数相同的学生id*/ /*第二步是查出至少有一门课程和01号同学不同的学生id*/ /*最后AND两个条件, 表示课程数相等,且学的课程相同即为完全相同*/ SELECT * FROM student WHERE s_id IN ( SELECT s_id FROM score WHERE s_id != '01' GROUP BY s_id HAVING COUNT(DISTINCT c_id)=(SELECT COUNT(DISTINCT c_id) FROM score where s_id='01') ) AND s_id NOT IN ( SELECT DISTINCT s_id FROM score WHERE c_id NOT IN ( SELECT sc.c_id FROM score sc WHERE sc.s_id='01' ) ); ``` 14、查询没学过"张三"老师讲授的任一门课程的学生姓名 ``` SELECT * FROM student st WHERE st.s_id NOT IN ( SELECT s.s_id FROM score s INNER JOIN course c ON s.c_id=c.c_id INNER JOIN teacher t ON t.t_id=c.t_id AND t.t_name='张三' ); ``` 15、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 st.s_id, st.s_name, AVG(sc.s_score) FROM student st INNER JOIN score sc ON st.s_id=sc.s_id WHERE st.s_id IN ( SELECT s_id FROM score WHERE s_score<60 GROUP BY s_id HAVING COUNT(DISTINCT c_id)>=2 ) GROUP BY st.s_id, st.s_name; ``` 16、检索"01"课程分数小于60，按分数降序排列的学生信息 ``` SELECT * FROM student st INNER JOIN score sc ON sc.s_id=st.s_id WHERE sc.s_score<60 AND sc.c_id='01' ORDER BY sc.s_score DESC; ``` 17、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 >备注：<br> >1.因为要选出需要的字段 用case when 当c_id='01' then 可以得到对应课程的s_core和课程名<br> >2.因为GROUP BY 要与select 列一致，所以用统计函数MAX加case when, 得到课程分数列<br> >3.因为每科成绩只有一个, 所以MAX取到的是