MySQL入门到精通经典50题学习笔记

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文章目录

• • MySQL入门到精通经典50题学习笔记
  • @[toc]
  • • • • MySQL安装教程详解
        • 数据预览
        • sql建表语句
        • 1.查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数
        • 2.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
        • 3.(略)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
        • 4.(略)查询姓“张”的老师个数
        • 5.查询没学过张三老师课的学生的学号和姓名
        • 6.查询学过张三老师所教的所有课程的同学的学号和姓名
        • 7.查询学过01课程并且学过02课程的学生
        • 8.(略)查询学过02课程的总成绩
        • 9.查询所有课程成绩小于60的学生
        • 10.查询没有学全所有课的学生学号、姓名(student为主表)
        • 11.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学号、姓名
        • 12.查询和“01”学号学生所学课程完全相同的学生学号
        • 13.查询没学过"张三"老师讲授的任一门课程的学生姓名
        • 15.查询两门及其以上不及格的同学的学号、姓名和平均成绩
        • 16.(略)检索01课程分数小于60 ，按课程分数降序排列学生信息
        • 17.按平均成绩从高到低显示所有学生的所有课程的成绩和平均成绩
        • 查询各科成绩最高分、最低分、平均分、及格率、中等率、优良率、优秀率
        • 19.按各科成绩进行排序，并显示排名
        • 20.(略)查询学生的总成绩并进行排名
        • 21.(略)查询不同老师所教不同课程平均分从高到低展示
        • 22.查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
        • 23.使用分段来统计各科成绩，分别统计各分数段人数：课程ID和课程名称
        • 24.查询学生平均成绩以及排名
        • 25.查询各科成绩前三名的记录（不考虑成绩并列情况）
        • 26.(略)查询每门课程被选修的学生数
        • 27.(略)查询出只有两门课程的全部学生的学号和姓名
        • 32.(略)查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩
        • 34.(略)查询课程名称为"数学"，且分数低于60分的学生姓名和分数
        • 35.查询所有学生的课程及分数情况
        • 36.查询任何一门课程成绩在70分以上的姓名、课程名称和分数
        • 37.(略)查询不及格的课程并按课程号从大到小排列
        • 38.(略)查询课程编号为03且课程成绩在80分以上的学生的学号和姓名
        • 40.查询选修“张三”老师所授课程的学生中成绩最高的学生姓名及其成绩
        • 41.查询某个不同课程但成绩相同的学生编号、课程编号、学生成绩
        • 42.查询每一门课程最好的前两名
        • 43.统计每门课程的学生选修人数（超过5人的课程才统计）
        • 44.检索至少选修两门课程的学生学号
        • 45.查询选修了全部课程的学生信息
        • 46.(略)查询各学生的年龄
        • 47.(略)查询本周过生日的学生
        • 48.查询下周过生日的学生
        • 49.(略)查询本月过生日的学生
        • 50.查询下月过生日的学生
        • 47.(略)查询本周过生日的学生
        • 48.查询下周过生日的学生
        • 49.(略)查询本月过生日的学生
        • 50.查询下月过生日的学生

MySQL安装教程详解

数据预览

• 

sql建表语句

• teacher表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80030
 Source Host           : localhost:3306
 Source Schema         : learn

 Target Server Type    : MySQL
 Target Server Version : 80030
 File Encoding         : 65001

 Date: 11/12/2022 12:24:34
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher`  (
  `TId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `Tname` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES ('01', '张三');
INSERT INTO `teacher` VALUES ('02', '李四');
INSERT INTO `teacher` VALUES ('03', '王五');

SET FOREIGN_KEY_CHECKS = 1;

• student表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80030
 Source Host           : localhost:3306
 Source Schema         : learn

 Target Server Type    : MySQL
 Target Server Version : 80030
 File Encoding         : 65001

 Date: 11/12/2022 12:24:27
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`  (
  `SId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `Sname` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `Sage` datetime NULL DEFAULT NULL,
  `Ssex` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('01', '赵雷', '1990-01-01 00:00:00', '男');
INSERT INTO `student` VALUES ('02', '钱电', '1990-12-21 00:00:00', '男');
INSERT INTO `student` VALUES ('03', '孙⻛', '1990-12-20 00:00:00', '男');
INSERT INTO `student` VALUES ('04', '李云', '1990-12-06 00:00:00', '男');
INSERT INTO `student` VALUES ('05', '周梅', '1991-12-01 00:00:00', '⼥');
INSERT INTO `student` VALUES ('06', '吴兰', '1992-01-01 00:00:00', '⼥');
INSERT INTO `student` VALUES ('07', '郑⽵', '1989-01-01 00:00:00', '⼥');
INSERT INTO `student` VALUES ('09', '张三', '2017-12-20 00:00:00', '⼥');
INSERT INTO `student` VALUES ('10', '李四', '2017-12-25 00:00:00', '⼥');
INSERT INTO `student` VALUES ('11', '李四', '2012-06-06 00:00:00', '⼥');
INSERT INTO `student` VALUES ('12', '赵六', '2013-06-13 00:00:00', '⼥');
INSERT INTO `student` VALUES ('13', '孙七', '2014-06-01 00:00:00', '⼥');

SET FOREIGN_KEY_CHECKS = 1;

• course表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80030
 Source Host           : localhost:3306
 Source Schema         : learn

 Target Server Type    : MySQL
 Target Server Version : 80030
 File Encoding         : 65001

 Date: 11/12/2022 12:24:11
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course`  (
  `CId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `Cname` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `TId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES ('01', '语⽂', '02');
INSERT INTO `course` VALUES ('02', '数学', '01');
INSERT INTO `course` VALUES ('03', '英语', '03');

SET FOREIGN_KEY_CHECKS = 1;

• sc表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80030
 Source Host           : localhost:3306
 Source Schema         : learn

 Target Server Type    : MySQL
 Target Server Version : 80030
 File Encoding         : 65001

 Date: 11/12/2022 12:24:21
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for sc
-- ----------------------------
DROP TABLE IF EXISTS `sc`;
CREATE TABLE `sc`  (
  `SId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `CId` varchar(10) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL,
  `score` decimal(18, 1) NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of sc
-- ----------------------------
INSERT INTO `sc` VALUES ('01', '01', 80.0);
INSERT INTO `sc` VALUES ('01', '02', 90.0);
INSERT INTO `sc` VALUES ('01', '03', 99.0);
INSERT INTO `sc` VALUES ('02', '01', 70.0);
INSERT INTO `sc` VALUES ('02', '02', 60.0);
INSERT INTO `sc` VALUES ('02', '03', 80.0);
INSERT INTO `sc` VALUES ('03', '01', 80.0);
INSERT INTO `sc` VALUES ('03', '02', 80.0);
INSERT INTO `sc` VALUES ('03', '03', 80.0);
INSERT INTO `sc` VALUES ('04', '01', 50.0);
INSERT INTO `sc` VALUES ('04', '02', 30.0);
INSERT INTO `sc` VALUES ('04', '03', 20.0);
INSERT INTO `sc` VALUES ('05', '01', 76.0);
INSERT INTO `sc` VALUES ('05', '02', 87.0);
INSERT INTO `sc` VALUES ('06', '01', 31.0);
INSERT INTO `sc` VALUES ('06', '03', 34.0);
INSERT INTO `sc` VALUES ('07', '02', 89.0);
INSERT INTO `sc` VALUES ('07', '03', 98.0);

SET FOREIGN_KEY_CHECKS = 1;

---

1.查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数

SELECT
	Student.*,
	01_score.CId,
	1_score,
	02_score.CId,
	2_score 
FROM
	Student
	JOIN ( SELECT SId, CId, score AS 1_score FROM SC WHERE CId = '01' ) AS 01_score ON Student.SId = 01_score.SId
	JOIN ( SELECT SId, CId, score AS 2_score FROM SC WHERE CId = '02' ) AS 02_score ON 01_score.SId = 02_score.SId 
WHERE
	1_score > 2_score;

2.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
	any_value ( sc.SId ) SId,
	any_value ( student.Sname ) Sname,
	avg( sc.score ) score 
FROM
	sc
	JOIN student ON sc.SId = student.SId 
GROUP BY
	sc.SId 
HAVING
	avg( sc.score ) > 60;

3.(略)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

SELECT
	any_value(student.Sname),
	any_value(student.SId),
	count( sc.CId ) course_count,
	IFNULL( sum( sc.score ), 0 ) all_score
FROM
	student
  left JOIN sc ON student.SId = sc.SId 
GROUP BY
	student.SId;

​

4.(略)查询姓“张”的老师个数

SELECT count(*)
from teacher
where Tname like '张%';

5.查询没学过张三老师课的学生的学号和姓名

-- 查询学习过张三老师课的学生
SELECT SId
from sc
	INNER JOIN course on course.CId = sc.CId
	INNER JOIN teacher on teacher.TId = course.TId
where Tname =  "张三";

-- 
SELECT
	student.SId,
	student.Sname 
FROM
	student 
WHERE
	SId NOT IN (
        SELECT
        SId 
        FROM
        sc
        INNER JOIN course ON course.CId = sc.CId
        INNER JOIN teacher ON teacher.TId = course.TId 
        WHERE
        Tname = "张三" 
    );

​

6.查询学过张三老师所教的所有课程的同学的学号和姓名

SELECT
	student.SId,
	student.Sname,
	course.Cname,
	teacher.Tname 
FROM
	sc
	INNER JOIN course ON sc.CId = course.CId
	INNER JOIN teacher ON teacher.TId = course.TId
	INNER JOIN student ON student.SId = sc.SId 
WHERE
	teacher.Tname = "张三";
ORDER BY
	student.SId;

7.查询学过01课程并且学过02课程的学生

-- 查询同时学习过01和02课程的同学
SELECT
	a.SId 
FROM
	( SELECT sc.SId FROM sc WHERE sc.CId = '01' ) AS a
	INNER JOIN ( SELECT sc.SId FROM sc WHERE sc.CId = '02' ) AS b ON a.SId = b.SId;
-- 综合
SELECT
	* 
FROM
	student 
WHERE
	student.SId in (
        SELECT
        a.SId 
        FROM
        ( SELECT sc.SId FROM sc WHERE sc.CId = '01' ) AS a
        INNER JOIN ( SELECT sc.SId FROM sc WHERE sc.CId = '02' ) AS b ON a.SId = b.SId
    );

8.(略)查询学过02课程的总成绩

SELECT
	sum( score ) 
FROM
	sc 
WHERE
	sc.CId = '02';

9.查询所有课程成绩小于60的学生

-- 查询成绩小于60分的学生以及课程数
SELECT
	sc.sid,
	count( sc.CId ) AS acount 
FROM
	sc 
WHERE
	sc.score < 60 
GROUP BY
	sc.SId;

-- 查询每个学生的课程数
SELECT
	sc.sid,
	count( sc.CId ) AS bcount 
FROM
	sc 
GROUP BY
	sc.sid;

-- 汇总
SELECT
	a.sid,
	student.Sname 
FROM
	( SELECT sc.sid, count( sc.CId ) AS acount FROM sc WHERE sc.score < 60 GROUP BY sc.SId ) a
	INNER JOIN ( SELECT sc.sid, count( sc.CId ) AS bcount FROM sc GROUP BY sc.sid ) b ON a.SId = b.sid
	INNER JOIN student ON student.SId = a.sid 
WHERE
	a.acount = b.bcount;

10.查询没有学全所有课的学生学号、姓名(student为主表)

-- 查询所有的课程数量
SELECT count(*) FROM course;
-- 查询每个学生的课程数
SELECT sc.SId, count(sc.CId) from sc GROUP BY sc.SId;
-- 查询课程数小于课程数量的sid
SELECT
	any_value ( student.sid ),
	any_value ( student.sname ) 
FROM
	student
	LEFT JOIN sc ON sc.sid = student.sid 
GROUP BY
	student.sid 
HAVING
	count( DISTINCT sc.cid ) < ( SELECT count( cid ) FROM course );

11.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学号、姓名

-- 查询01号学生的课程号 
SELECT sc.CId from sc WHERE sc.SId = '01';
-- 查询课程号在01号学生中的学生
SELECT DISTINCT sc.SId
from sc
WHERE sc.CId in (SELECT sc.CId from sc WHERE sc.SId = '01')
and sc.SId != '01';
-- 汇总
SELECT
	student.SId,
	student.Sname 
FROM
	student
	INNER JOIN (
        SELECT DISTINCT
        sc.SId 
        FROM
        sc 
        WHERE
        sc.CId IN ( SELECT sc.CId FROM sc WHERE sc.SId = '01' ) 
        AND sc.SId != '01' 
    ) a ON a.SId = student.SId;

​

12.查询和“01”学号学生所学课程完全相同的学生学号

SELECT
	* 
FROM
	student 
WHERE
	SId IN (SELECT SId FROM (
        SELECT * FROM sc a WHERE CId IN ( SELECT CId FROM sc WHERE SId = 01 )) b 
            GROUP BY SId 
            HAVING count( CId ) =(SELECT count( CId ) FROM sc c WHERE SId = 01 )) 
	AND SId != 01;

13.查询没学过"张三"老师讲授的任一门课程的学生姓名

-- 查询张三老师讲授的课程
SELECT CId 
from 
	course, teacher
WHERE
	course.TId = teacher.TId
and 
	teacher.Tname = "张三";

-- 学过张三老师课程的学生
SELECT sc.SId 
from
	sc
	INNER JOIN course on course.CId = sc.CId
	INNER JOIN teacher on teacher.TId = course.TId
	AND teacher.Tname = "张三";


SELECT
	* 
FROM
	student 
WHERE
	SId NOT IN (
        SELECT
        sc.SId 
        FROM
        sc
        INNER JOIN course ON course.CId = sc.CId
        INNER JOIN teacher ON teacher.TId = course.TId 
        AND teacher.Tname = "张三" 
    );

​

15.查询两门及其以上不及格的同学的学号、姓名和平均成绩

SELECT
	any_value(sc.SId),
	any_value(student.Sname),
	AVG( sc.score ) 
FROM
	sc
	INNER JOIN student ON sc.SId = student.SId 
WHERE
	sc.score < 60 GROUP BY sc.SId HAVING count( DISTINCT sc.CId ) >= 2;

-- 查询每个学生成绩不及格的门数
SELECT SId,count(*) 
from sc
WHERE sc.score < 60
GROUP BY SId;

16.(略)检索01课程分数小于60 ，按课程分数降序排列学生信息

SELECT student.SId,Sname, sc.score
from 
	student
	INNER JOIN sc on student.SId = sc.SId
WHERE
	sc.score < 60 and sc.CId = 01
ORDER BY sc.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和平均成绩

SELECT
	sc.sid,
	max( CASE WHEN sc.cid = '01' THEN sc.score ELSE NULL END ) '语文',
	max( CASE WHEN sc.cid = '02' THEN sc.score ELSE NULL END ) '数学',
	max( CASE WHEN sc.cid = '03' THEN sc.score ELSE NULL END ) '英语',
	avg( sc.score ) 
FROM
	sc 
GROUP BY
	sc.sid 
ORDER BY
	avg( sc.score ) DESC;

18. 查询各科成绩最高分、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
SELECT 
	sc.CId,
	course.Cname,
  max(sc.score),
	min(sc.score),
	avg(sc.score),
	sum(CASE WHEN sc.score >= 60 THEN 1 ELSE 0 END) / count(sc.SId) '及格',
	sum(CASE WHEN sc.score >= 70 and sc.score < 80 THEN 1 ELSE 0 END) / count(sc.SId) '中等',
	sum(CASE WHEN sc.score >= 80 and sc.score < 90 THEN 1 ELSE 0 END) / count(sc.SId) '优良',
	sum(CASE WHEN sc.score >= 90 THEN 1 ELSE 0 END) / count(sc.SId) '优秀'
from sc
	INNER JOIN course on course.CId = sc.CId
GROUP BY sc.CId, course.Cname;

​

19.按各科成绩进行排序，并显示排名

SELECT
	sc.sid,
	sc.cid,
	course.Cname,
	sc.score,
	ROW_NUMBER() over ( ORDER BY sc.CId, sc.score DESC ) 
FROM
	sc
	INNER JOIN course on course.CId = sc.CId;

​

20.(略)查询学生的总成绩并进行排名

SELECT
	any_value(sc.SId),
	any_value(student.Sname),
	sum(sc.score) grade
from sc
	INNER JOIN student on student.SId = sc.SId
GROUP BY sc.SId
ORDER BY grade desc;

​

21.(略)查询不同老师所教不同课程平均分从高到低展示

SELECT 
	any_value(teacher.Tname),
	sc.CId,
	avg(sc.score)
from 
	sc
	INNER JOIN course on course.CId = sc.CId
	INNER JOIN teacher on teacher.TId = course.TId
GROUP BY sc.CId
ORDER BY AVG(sc.score) desc;

22.查询所有课程的成绩第2名到第3名的学生信息及该课程成绩

SELECT 
	any_value(student.Sname),
	any_value(sc.SId),
	sum(sc.score) grade
from sc
	INNER JOIN student on student.SId = sc.SId
GROUP BY sc.SId
ORDER BY grade desc
LIMIT 1, 2;

23.使用分段来统计各科成绩，分别统计各分数段人数：课程ID和课程名称

SELECT 
	sc.CId,
	any_value(course.Cname),
	sum(case WHEN sc.score < 60 THEN 1 else 0 end) '60以下',
	sum(case WHEN sc.score >= 60 and sc.score < 70 THEN 1 else 0 end) '60-70',
	sum(case WHEN sc.score >= 70 and sc.score < 80 THEN 1 else 0 end) '70-80',
	sum(case WHEN sc.score >= 80 and sc.score < 90 THEN 1 else 0 end) '80-90',
	sum(case WHEN sc.score >= 90 THEN 1 else 0 end) '90以上'
from 
	sc
	INNER JOIN course on course.CId = sc.CId
GROUP BY sc.CId;

24.查询学生平均成绩以及排名

SELECT
	sc.SId,
	any_value(student.Sname),
	avg( sc.score ) grade 
FROM
	sc
	INNER JOIN student on student.SId = sc.SId 
GROUP BY
	sc.SId 
ORDER BY
	grade DESC;

​

25.查询各科成绩前三名的记录（不考虑成绩并列情况）

-- PARTITION BY作用于分组之下的排序，与group by类似，但是有区别
-- 进行每个科目的排序
SELECT
	*,
	ROW_NUMBER() over ( PARTITION BY sc.cid ORDER BY sc.score DESC ) m 
FROM
	sc
	INNER JOIN student stu ON stu.sid = sc.sid

-- 汇总结果
-- 窗口函数
SELECT
	*
FROM
	(
        SELECT
        student.SId, sc.CId, sc.score, student.Sname, student.Sage, student.Ssex, 
        ROW_NUMBER() over ( PARTITION BY sc.cid ORDER BY sc.score DESC ) m 
        FROM
        sc
        INNER JOIN student ON student.sid = sc.sid 
    ) a 
WHERE
	m IN ( 1,2, 3 )

​

26.(略)查询每门课程被选修的学生数

SELECT 
	sc.CId,
	count(sc.SId)
from sc
GROUP BY sc.CId;
-- 答案
SELECT
	course.cid,
	count( sc.sid ) 
FROM
	sc
	INNER JOIN course ON sc.CId = course.cid 
GROUP BY
	course.cid

27.(略)查询出只有两门课程的全部学生的学号和姓名

SELECT student.SId, any_value(student.Sname)
from student
	INNER JOIN sc on sc.SId = student.SId
GROUP BY student.SId
HAVING count(sc.CId) = 2;


-- 28.(略)查询男生、女生人数
SELECT 
	student.Ssex,
	count(student.Ssex)
from student
GROUP BY student.Ssex;

29. (略)查询名字中含有"三"字的学生信息

SELECT *
from student
WHERE student.Sname like "%三%";

31.查询1990年出生的学生名单

SELECT *
from student
WHERE year(student.Sage) = 1990;

-- 或者是用like
SELECT
	student.sid,
	student.sname 
FROM
	student 
WHERE
	student.sage LIKE '1990%';

32.(略)查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩

SELECT student.SId, any_value(student.Sname), avg(sc.score) avg_score
FROM student 
	INNER JOIN sc on sc.SId = student.SId
GROUP BY student.SId
HAVING avg_score >= 85;

33.(略)查询每门课程的平均成绩，结果按平均成绩升序排序，平均成绩相同时，

-- 按课程号降序排列
SELECT 
	sc.CId, 
	avg(sc.score)
from sc
GROUP BY sc.CId
ORDER BY avg(sc.score) asc, sc.CId DESC;

34.(略)查询课程名称为"数学"，且分数低于60分的学生姓名和分数

SELECT student.Sname, sc.score
from student
	INNER JOIN sc on student.SId = sc.SId
	INNER JOIN course on course.CId = sc.CId and course.Cname = "数学"
WHERE
	sc.score < 60;

35.查询所有学生的课程及分数情况

SELECT
	student.sid,
	any_value(student.sname),
	max( CASE WHEN course.cname = '语文' THEN sc.score ELSE NULL END ) '语文',
	max( CASE WHEN course.cname = '数学' THEN sc.score ELSE NULL END ) '数学',
	max( CASE WHEN course.cname = '英语' THEN sc.score ELSE NULL END ) '英语' 
FROM
	student
	INNER JOIN sc ON sc.sid = student.sid
	INNER JOIN course ON sc.CId = course.CId 
GROUP BY
	student.sid;

​

36.查询任何一门课程成绩在70分以上的姓名、课程名称和分数

SELECT student.SId, student.Sname, course.Cname, sc.score
from student
	INNER JOIN sc on sc.SId = student.SId
	INNER JOIN course on course.CId = sc.CId
WHERE sc.score > 70;

37.(略)查询不及格的课程并按课程号从大到小排列

SELECT
	student.sid,
	student.sname,
	course.cname,
	sc.cid,
	sc.score 
FROM
	sc
	INNER JOIN course ON course.cid = sc.cid
	INNER JOIN student ON student.sid = sc.SId 
WHERE
	sc.score < 60 
ORDER BY
	sc.cid DESC;

38.(略)查询课程编号为03且课程成绩在80分以上的学生的学号和姓名

SELECT student.SId, student.Sname, sc.score
from student
	INNER JOIN sc on sc.SId  = student.SId and sc.CId = 03
WHERE sc.score > 80;


-- 39.(略)求每门课程的学生人数
SELECT any_value(course.Cname), count(DISTINCT course.CId)
from course
	INNER JOIN sc on sc.CId  = course.CId
GROUP BY sc.CId;

40.查询选修“张三”老师所授课程的学生中成绩最高的学生姓名及其成绩

SELECT 
	any_value(student.SId), any_value(student.Sname), 
	any_value(sc.CId),any_value(course.Cname),
	max(sc.score)
from student
	INNER JOIN sc on sc.SId = student.SId
	INNER JOIN course on course.CId = sc.CId
	INNER JOIN teacher on teacher.TId = course.TId
WHERE teacher.Tname = "张三";

41.查询某个不同课程但成绩相同的学生编号、课程编号、学生成绩

SELECT
	sid 
FROM
	(SELECT b.sid,b.score 
     FROM sc AS b
     INNER JOIN ( SELECT sid FROM sc GROUP BY sid HAVING count( DISTINCT cid )> 1 ) AS c ON b.sid = c.sid 
     GROUP BY
     b.sid,
     b.score 
    ) AS a 
GROUP BY sid HAVING	count( sid )=1

42.查询每一门课程最好的前两名

SELECT a.CId, a.SId, any_value(a.score)
from sc a
	LEFT JOIN sc b
	on a.CId = b.CId
	and a.score < b.score	
	GROUP BY a.CId, a.SId
HAVING count(a.CId) < 2;

43.统计每门课程的学生选修人数（超过5人的课程才统计）

-- 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
SELECT sc.CId, count(sc.SId) as cnt
from sc
GROUP BY sc.CId
HAVING cnt > 5
ORDER BY cnt DESC, sc.CId ASC;

44.检索至少选修两门课程的学生学号

SELECT sc.SId, any_value(student.Sname), count(sc.CId) cnt
from sc
	INNER JOIN student on student.SId = sc.SId
GROUP BY sc.SId
HAVING cnt >= 2;

45.查询选修了全部课程的学生信息

SELECT sc.SId, any_value(student.Sname), count(sc.CId) cnt
from sc
	INNER JOIN student on student.SId = sc.SId
GROUP BY sc.SId
HAVING cnt = (SELECT count(*) from course);


-- 日期类函数
SELECT NOW();
SELECT CURDATE();
SELECT CURTIME();
SELECT DATE("2022-12-10");

46.(略)查询各学生的年龄

SELECT
	student.Sname,
	TIMESTAMPDIFF(
        YEAR,
        student.Sage,
        CURTIME()) 
FROM
	student;

47.(略)查询本周过生日的学生

SELECT
	* 
FROM
	student 
WHERE 
	WEEK(Sage, 1) = WEEK(NOW(), 1);

-- WEEKOFYEAR() 和 CURDATE()。WEEKOFYEAR() 函数用于获取某个日期所在的周，而 CURDATE() 函数用于获取当前日期。
SELECT * from student
WHERE WEEKOFYEAR(student.Sage) = WEEKOFYEAR(CURDATE());

48.查询下周过生日的学生

-- 如果想要查询的是下一周过生日的学生，可以把 CURDATE() 替换为 CURDATE() + INTERVAL 7 DAY
SELECT * from student WHERE 
WEEKOFYEAR(student.Sage) = WEEKOFYEAR(CURDATE() + INTERVAL 7 day);

49.(略)查询本月过生日的学生

SELECT * from student
WHERE MONTH(student.Sage) = MONTH(CURDATE());

50.查询下月过生日的学生

SELECT * from student
WHERE MONTH(student.Sage) = MONTH(CURDATE() + INTERVAL 1 MONTH);

d
GROUP BY sc.SId
HAVING cnt = (SELECT count(*) from course);

– 日期类函数
SELECT NOW();
SELECT CURDATE();
SELECT CURTIME();
SELECT DATE(“2022-12-10”);

##### 46.(略)查询各学生的年龄

```sql
SELECT
	student.Sname,
	TIMESTAMPDIFF(
        YEAR,
        student.Sage,
        CURTIME()) 
FROM
	student;

47.(略)查询本周过生日的学生

SELECT
	* 
FROM
	student 
WHERE 
	WEEK(Sage, 1) = WEEK(NOW(), 1);

-- WEEKOFYEAR() 和 CURDATE()。WEEKOFYEAR() 函数用于获取某个日期所在的周，而 CURDATE() 函数用于获取当前日期。
SELECT * from student
WHERE WEEKOFYEAR(student.Sage) = WEEKOFYEAR(CURDATE());

48.查询下周过生日的学生

-- 如果想要查询的是下一周过生日的学生，可以把 CURDATE() 替换为 CURDATE() + INTERVAL 7 DAY
SELECT * from student WHERE 
WEEKOFYEAR(student.Sage) = WEEKOFYEAR(CURDATE() + INTERVAL 7 day);

49.(略)查询本月过生日的学生

SELECT * from student
WHERE MONTH(student.Sage) = MONTH(CURDATE());

50.查询下月过生日的学生

SELECT * from student
WHERE MONTH(student.Sage) = MONTH(CURDATE() + INTERVAL 1 MONTH);