From d8638ef75a6294c658e3c5d93a4d536d6b8397eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=88=98=E5=B0=91=E6=B5=B7?= <3087930763@qq.com>
Date: Fri, 3 Mar 2023 21:27:39 +0800
Subject: [PATCH] =?UTF-8?q?20230227=20MySQL=E7=9A=84=E5=85=B3=E8=81=94?=
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+```mysql 
+USE guanlian;
+-- -- 1,查询所有学生，都学了哪些课程，要显示学生信息和课程信息/
+SELECT * FROM student INNER JOIN score ON student.Sno = score.Sno;
+-- -- 2，查询没有学生的教师的所有信息
+SELECT * FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON course.Cno = score.Cno
+WHERE Sno is NULL;
+-- ①　查询Score表中的最高分的学生学号和课程号。
+SELECT MAX(Degree) FROM score;
+SELECT Degree,Sno,Cno FROM score WHERE Degree = (SELECT MAX(Degree) FROM score);
+-- ②　查询所有学生的Sname、Cno和Degree列。
+SELECT student.`name`,score.Cno,score.Degree FROM student INNER JOIN score ON student.Sno = score.Sno;
+-- ③　查询所有学生的Sno、Cname和Degree列。
+SELECT score.Sno,course.Cname,score.Degree FROM score INNER JOIN course on score.Cno = course.Cno;
+-- ④　查询所有学生的Sname、Cname和Degree列。
+SELECT student.`name`,course.Cname,score.Degree FROM student 
+LEFT JOIN score on student.Sno = score.Sno 
+LEFT JOIN course on score.Cno = course.Cno;
+-- ⑤　查询“95033”班学生的平均分。
+SELECT Sno FROM student WHERE Class = 95033;
+SELECT SUM(Degree) FROM score WHERE Sno IN(101,107,108);
+SELECT AVG(Degree) FROM score WHERE Sno IN(SELECT Sno FROM student WHERE Class = 95033);
+-- SELECT * FROM student INNER JOIN score ON student.Sno = score.Sno WHERE Class = 95033;
+-- ⑥　查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录。
+SELECT Degree FROM score WHERE Sno = 109 AND Cno = '3-105'
+SELECT * FROM score WHERE Cno = '3-105' AND Degree>(SELECT Degree FROM score WHERE Sno = 109 AND Cno = '3-105');
+-- ⑦　查询score中选学多门课程的同学中分数为非最高分成绩的记录。
+SELECT MAX(Degree) FROM score;
+SELECT Sno,Cno,Degree FROM score WHERE Degree != (SELECT MAX(Degree) FROM score);
+-- ⑧　查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。
+SELECT Degree FROM score WHERE Sno = 109 AND Cno = '3-105';
+SELECT * FROM score WHERE Degree>(SELECT Degree FROM score WHERE Sno = 109 AND Cno = '3-105');
+-- ⑨　查询和学号为108的同学同年出生的所有学生的Sno、Sname和Sbirthday列
+SELECT YEAR(Sbirthday) FROM student WHERE Sno = 108;
+SELECT * FROM student WHERE Sno = 108 AND ;
+SELECT sno,`name`,Sbirthday FROM student WHERE Sbirthday = (SELECT YEAR(Sbirthday) FROM student WHERE Sno = 108);
+-- ⑩　查询“张旭“教师任课的学生成绩。
+SELECT Degree FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON score.Cno = course.Cno
+WHERE score.Cno = '6-166'
+-- ⑪　查询选修某课程的同学人数多于5人的教师姓名。？
+SELECT COUNT(Cno) FROM score GROUP BY Cno;
+SELECT * FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON course.Cno = score.Cno
+WHERE score.Cno = '3-105'
+-- ⑫　查询出“计算机系“教师所教课程的成绩表。
+SELECT * FROM teacher WHERE Depart = '计算机系'
+SELECT * FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON course.Cno = score.Cno
+WHERE course.Cno IN('3-105','3-245')
+-- ⑬　查询“计算机系”与“电子工程系“不同职称的教师的Tname和Prof。
+SELECT Tname,Prof FROM teacher WHERE Depart IN('计算机系','电子工程系');
+--  ⑭　查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的Cno、Sno和Degree,并按Degree从高到低次序排序。
+SELECT Degree FROM score WHERE Cno = '3-105'
+SELECT Degree FROM score WHERE Cno = '3-245'
+SELECT * FROM score WHERE Cno in ('3-105','3-245');
+select Cno,Sno,Degree from score where cno='3-105' and degree >any(select degree from score where cno='3-245' ) order by degree  DESC
+-- ⑮　查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的Cno、Sno和Degree.
+SELECT * FROM score WHERE Cno = '3-105' AND Degree > ALL(SELECT Degree FROM score WHERE Cno = '3-245') ORDER BY Degree DESC;
+-- SELECT * FROM (SELECT * FROM score WHERE Cno IN ('3-105','3-245')) AS S WHERE Cno = '3-105' AND Degree > IN (SELECT Degree FROM score WHERE Cno = '3-245');
+-- SELECT * FROM score WHERE Degree > (SELECT Degree FROM score WHERE Cno = '3-245' || Cno = '3-105');
+-- -- ⑯　查询成绩比该课程平均成绩低的同学的成绩表。
+SELECT * FROM score WHERE Cno = '3-105';
+SELECT AVG(Degree) FROM score WHERE Cno = '3-105';
+SELECT * FROM (SELECT * FROM score WHERE Cno = '3-105') AS S WHERE Degree<(SELECT AVG(Degree) FROM score WHERE Cno = '3-105');
+-- ⑰　查询所有任课教师的Tname和Depart.
+SELECT DISTINCT Tname,Depart FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON score.Cno = course.Cno
+WHERE score.Cno is NOT NULL
+-- ⑱　查询所有未讲课的教师的Tname和Depart.
+SELECT DISTINCT Tname,Depart FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON score.Cno = course.Cno
+WHERE score.Cno is NULL
+-- ⑲　查询“男”教师及其所上的课程。
+SELECT * FROM teacher 
+LEFT JOIN course ON teacher.Tno = course.Tno
+LEFT JOIN score ON score.Cno = course.Cno
+WHERE score.Cno is NOT NULL AND Tsex = '男'
+-- ⑳　查询最高分同学的Sno、Cno和Degree列。
+SELECT Sno,Cno,Degree FROM score WHERE Degree = (SELECT MAX(Degree)FROM score)
+-- 21　查询和“李军”同性别的所有同学的Sname.
+SELECT `name` FROM student WHERE Seax = '男' AND `name` != '李军'
+-- 22　查询和“李军”同性别并同班的同学Sname.
+SELECT Class FROM student WHERE `name` = '李军'
+SELECT * FROM student WHERE Seax = '男' AND Class = (SELECT Class FROM student WHERE `name` = '李军')
+-- 23　查询所有选修“计算机导论”课程的“男”同学的成绩表。
+SELECT * FROM score 
+LEFT JOIN student ON score.Sno = student.Sno
+LEFT JOIN course ON score.Cno = course.Cno
+WHERE student.Seax = '男' AND course.Cname = '计算机导论'
+```
+
+```MySQL
+max (字段)查询最大值
+min (字段)查询最低值
+avg (字段)查询平均值
+any ()：括号内任意一个
+all ()：括号内的全部
+select 字段列表 from 数据表1 inner join 数据表名称2 on 数据表名称1.相同数据类型的字段 = 数据表2.相同数据类型的字段 ——————内连接
+select 字段列表 from 数据表1 left join 数据表名称2 on 数据表名称1.相同数据类型的字段 = 数据表2.相同数据类型的字段  ——————左连接
+select 字段列表 from 数据表1 right join 数据表名称2 on 数据表名称1.相同数据类型的字段 = 数据表2.相同数据类型的字段  ——————右连接
+```
+
-- 
Gitee