Mysql复杂语句查询

1.自行添加测试数据

2.查询平均成绩大于60分的同学的学号和平均成绩； 

SELECT t1.sid,AVG(t2.number)
FROM student t1 LEFT JOIN score t2 ON t1.sid=t2.student_id
GROUP BY t1.sid HAVING AVG(t2.number)>60;

3.查询所有同学的学号、姓名、选课数、总成绩；

SELECT t1.sid,t1.sname,t2.temp1,t3.temp2
FROM student t1,(SELECT student_id,COUNT(sid) temp1 FROM score GROUP BY student_id) t2,
(SELECT student_id,SUM(number) temp2 FROM score GROUP BY student_id) t3
WHERE t1.sid=t2.student_id AND t1.sid=t3.student_id;
#较复杂，有难度

4.查询姓“李”的老师的个数；

SELECT COUNT(tid)
FROM teacher
WHERE tname LIKE '李%';

5.查询没学过“叶平”老师课的同学的学号、姓名；

SELECT t1.`sid`,t1.`sname`
FROM student t1
WHERE t1.`sid` NOT IN(SELECT student_id
FROM score
WHERE course_id IN(SELECT t2.cid
FROM teacher t1 LEFT JOIN course t2 ON t1.`tid`=t2.`teacher_id`
WHERE t1.tname='叶平' ORDER BY t2.`cid`));
#子句
SELECT student_id
FROM score
WHERE course_id IN(SELECT t2.cid
FROM teacher t1 LEFT JOIN course t2 ON t1.`tid`=t2.`teacher_id`
WHERE t1.tname='叶平' ORDER BY t2.`cid`);<br>#较复杂

6.查询学过“001”并且也学过编号“002”课程的同学的学号、姓名

#方法2 SELECT t1.sid,t1.sname FROM (SELECT t1.`student_id` sid,t2.`sname` sname FROM score t1 LEFT JOIN student t2 ON t1.`student_id`=t2.`sid` WHERE course_id=1 UNION ALL SELECT t1.`student_id`,t2.`sname` FROM score t1 LEFT JOIN student t2 ON t1.`student_id`=t2.`sid` WHERE course_id=2) t1 GROUP BY t1.sid HAVING COUNT(*)>1;

7.查询学过“叶平”老师所教的所有课的同学的学号、姓名；

SELECT  distinct t1.`student_id`,t2.`sname`
FROM score t1 LEFT JOIN student t2 ON t1.`student_id`=t2.`sid`
WHERE t1.`course_id` IN(SELECT t2.cid
FROM teacher t1 LEFT JOIN course t2 ON t1.`tid`=t2.`teacher_id`
WHERE t1.tname='叶平' ORDER BY t2.`cid`);
#子句
SELECT t2.cid
FROM teacher t1 LEFT JOIN course t2 ON t1.`tid`=t2.`teacher_id`
WHERE t1.tname='叶平' ORDER BY t2.`cid`;

8.查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；

#子句1
SELECT number
FROM score
WHERE course_id=2;
#子句2
SELECT number
FROM score t1
WHERE t1.`course_id`=1;
#总语句
SELECT t3.`sid`,t3.`sname`
FROM (SELECT student_id,number
FROM score
WHERE course_id=2) t1,(SELECT student_id,number
FROM score
WHERE course_id=1) t2,student t3
WHERE t1.student_id=t3.sid AND t2.student_id=t3.sid AND t1.number<t2.number;

9.查询有课程成绩小于60分的同学的学号、姓名；

#方法1
SELECT DISTINCT t1.student_id,t2.`sname`
FROM score t1 LEFT JOIN student t2 ON t1.`student_id`=t2.`sid`
WHERE t1.number<60;
#方法2
SELECT t1.sid,t1.sname
FROM student t1,(SELECT student_id FROM score WHERE number<60 GROUP BY student_id) t2
WHERE t1.sid=t2.student_id;

10.查询没有学全所有课的同学的学号、姓名；

#总语句
SELECT sid,sname
FROM student
WHERE sid NOT IN(SELECT student_id
FROM score
GROUP BY student_id HAVING COUNT(course_id)=(SELECT COUNT(cid) FROM course));
#子句
SELECT sid,sname
FROM student
WHERE sid NOT IN();
#子句：学全了的学生编号
SELECT student_id
FROM score
GROUP BY student_id HAVING COUNT(course_id)=(SELECT COUNT(cid) FROM course);
#子句：课程的总数
SELECT COUNT(cid) FROM course;

11.查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；

#总语句
SELECT DISTINCT t1.student_id,t2.`sname`
FROM score t1 LEFT JOIN student t2 ON t1.`student_id`=t2.`sid`
WHERE course_id IN(SELECT course_id
FROM score
WHERE student_id=1);
#子句:学号1所选所有课程
SELECT course_id
FROM score
WHERE student_id=1

原文地址：https://www.cnblogs.com/dldrjyy13102/p/7702979.html