mysql查询

-- 10.21   SQL练习

-- 表结构和数据参见4个.sql文件

-- 1、查询“c001”课程比“c002”课程成绩高的所有学生的学号；

select s1.sid from (

SELECT sid,score from sc where cid='001') s1

join (

SELECT sid,score from sc where cid='002') s2

on s1.sid=s2.sid

where s1.score > s2.score;

 

-- 2、查询平均成绩大于60 分的同学的学号和平均成绩；

SELECT sc.sid, AVG(sc.score) FROM sc

GROUP BY sc.sid

HAVING AVG(sc.score) >60;

 

-- 3、查询所有同学的学号、姓名、选课数、总成绩；

SELECT sc.sid ,

student.sname AS 姓名,

COUNT(sc.sid) AS 选课数,

SUM(sc.score) AS 总成绩

FROM sc JOIN student

ON sc.sid=student.sid

GROUP BY sc.sid;

 

-- 4、查询姓“刘”的老师的个数；

SELECT COUNT(tName) FROM teacher

WHERE tName LIKE "%李%";

 

-- 5、查询没学过“李老师”课的同学的学号、姓名；

 

 

-- 6、查询学过“c001”并且也学过编号“c002”课程的同学的学号、姓名；

-- 7、查询学过“李老师”所教的所有课的同学的学号、姓名；

-- 8、查询课程编号“c002”的成绩比课程编号“c001”课程低的所有同学的学号、姓名；

-- 9、查询所有课程成绩小于60 分的同学的学号、姓名；

-- 10、查询没有学全所有课的同学的学号、姓名；

 

 

 

 

-- 10.21   SQL练习

-- 表结构和数据参见4个.sql文件

-- 1、查询“c001”课程比“c002”课程成绩高的所有学生的学号；

SELECT

       s1.sid

FROM

       ( SELECT sid, score FROM sc WHERE cid = '001' ) s1

       JOIN ( SELECT sid, score FROM sc WHERE cid = '002' ) s2 ON s1.sid = s2.sid

WHERE

       s1.score > s2.score;-- 2、查询平均成绩大于60 分的同学的学号和平均成绩

SELECT

       sc.sid,

       AVG( sc.score )

FROM

       sc

GROUP BY

       sc.sid

HAVING

       AVG( sc.score ) > 60;-- 3、查询所有同学的学号、姓名、选课数、总成绩；

SELECT

       sc.sid,

       student.sname AS 姓名,

       COUNT( sc.sid ) AS 选课数,

       SUM( sc.score ) AS 总成绩

FROM

       sc

       JOIN student ON sc.sid = student.sid

GROUP BY

       sc.sid;-- 4、查询姓“刘”的老师的个数；

SELECT

       COUNT( tName )

FROM

       teacher

WHERE

       tName LIKE "%李%";-- 5、查询没学过“李老师”课的同学的学号、姓名；

#查询李老师的tid是多少

-- SELECT teacher.tid FROM teacher

-- WHERE teacher.tName="李老师";

#查询李老师的课有哪些

SELECT

       course.cid

FROM

       course

       RIGHT JOIN ( SELECT teacher.tid FROM teacher WHERE teacher.tName = "李老师" ) ON teacher.tid = course.tid;--