Mysql整理二 - 常见查询语句面试题(附原表)

表结构，创建原表的代码在最后

-- cid课程id; tid老师id; sid学生id;
select * from t_mysql_course;
select * from t_mysql_score;
select * from t_mysql_student;
select * from t_mysql_teacher;

1. 查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数

-- 查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数
-- 把课程01和课程02单独拉出来，再进行对比，为了确保能对应成功，需要s1.sid = s.sid这个条件
-- 为了确保对比的是同一个人，需要有s1.sid = s2.sid
select s.*,s1.score a, s2.score b
from
t_mysql_student s,
(select * from t_mysql_score where cid = "01") s1,
(select * from t_mysql_score where cid = "02") s2
where
s1.sid = s2.sid and
s1.sid = s.sid and
s1.score > s2.score;

2. 查询同时存在 " 01 “课程和” 02 "课程的情况 SELECT

-- 查询同时存在 " 01 “课程和” 02 "课程的情况 
select s1.sid from 
(select * from t_mysql_score where cid = "01") as s1 
inner join
(select * from t_mysql_score where cid = "02") as s2
where s1.sid = s2.sid;

3. 查询存在 " 01 “课程但可能不存在” 02 "课程的情况 ( 不存在时显示为 NULL ) 

-- 查询不存在" 01 “课程但存在” 02 "课程的情况
select s.* from t_mysql_score s where sid 
not in (select sid from t_mysql_score where cid = "01") and s.cid = "02";

4. 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

-- 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 s.sid,s.sname,s2.score from t_mysql_student s
, (select sid,avg(score) as score from t_mysql_score group by sid) as s2 
where s.sid = s2.sid and s2.score >= 60;

5. 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(没成绩的显示为 null)

-- 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(没成绩的显示为 null)
select s.sid,s.sname,s2.num_cid,s2.sum_score 
from t_mysql_student s,
(select s1.sid,count(cid) as num_cid,sum(score) as sum_score from t_mysql_score s1 group by sid) as s2
where s.sid = s2.sid;

6. 查询学过「张三」老师授课的同学的信息

-- 查询学过「张三」老师授课的同学的信息

select st.sid,st.sname,st.sage,st.ssex from t_mysql_student st,
t_mysql_course co, 
t_mysql_score sc, 
t_mysql_teacher te
where te.tname like '张三' and 
te.tid = co.tid and 
co.cid = sc.cid and 
sc.sid = st.sid;

7. 查询没有学全所有课程的同学的信息

-- 查询没有学全所有课程的同学的信息
select s.*, COUNT(sc.cid) as count_cid 
from t_mysql_student s 
join t_mysql_score sc 
on s.sid = sc.sid 
group by sc.sid 
having 
COUNT(sc.cid) < (select count(*) from t_mysql_course);

8. 查询没学过"张三"老师讲授的任一门课程的学生姓名

-- 查询没学过"张三"老师讲授的任一门课程的学生姓名
select * from t_mysql_student where sid 
not in 
(select sc.sid from t_mysql_course co, t_mysql_score sc, t_mysql_teacher te
where te.tname like '张三' and te.tid = co.tid and co.cid = sc.cid);

9. 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

-- 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 s.sid,s.sname,round(avg(sc.score),2) as score 
from t_mysql_student s,t_mysql_score sc
where s.sid = sc.sid
and sc.score < 60 group by sid having count(sc.cid) >= 2;

10. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息

-- 检索" 01 "课程分数小于 60，按分数降序排列的学生信息
select 
s.sid,s.sname,sc.score
from 
t_mysql_student s,t_mysql_score sc
where 
s.sid = sc.sid
and sc.score < 60 
and sc.cid = "01" 
order by score desc;

11. 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

-- 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
select 
s.sname,s.sid,round(avg(sc.score),2) as avg_score,
max(CASE WHEN sc.cid = "01" THEN sc.score END )语文,
max(CASE WHEN sc.cid = "02" THEN sc.score END )数学,
max(CASE WHEN sc.cid = "03" THEN sc.score END )英语
from 
t_mysql_student s,t_mysql_score sc
where 
s.sid = sc.sid 
group by s.sid
order by avg(sc.score) desc;

12. -- 以如下形式显示：课程 ID，课程 name，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
-- 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

-- 以如下形式显示：课程 ID，课程 name，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
-- 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
co.cid, co.cname, max(sc.score) 最高分, min(sc.score) 最低分, round(avg(sc.score),2) 平均分,
concat(round(sum(if (sc.score > 60, 1,0))/count(sc.score)*100,2),'%') 及格率
from t_mysql_course co,t_mysql_score sc
where co.cid = sc.cid
group by co.cid;

SUM(IF(sc.score > 60, 1, 0))：这部分计算了成绩大于 60 分的记录的数量。
如果某条记录的成绩大于 60 分，那么 IF 函数返回 1，否则返回 0。然后，
SUM 函数将这些值相加，得到及格的记录数。

COUNT(sc.score)：这部分计算了总记录数，无论成绩是否及格。

sum(...) / count(sc.score)：这部分计算及格的记录数除以总记录数，得到及格率。

ROUND(..., 2)：这部分使用 ROUND 函数将计算结果保留两位小数。

CONCAT(..., '%')：最后，CONCAT 函数将计算结果和百分号字符 "%" 连接在一起，
得到一个带百分号的及格率字符串。

13. 原表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80018
 Source Host           : localhost:3306
 Source Schema         : mybatis_ssm

 Target Server Type    : MySQL
 Target Server Version : 80018
 File Encoding         : 65001

 Date: 04/07/2023 23:53:33
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for t_mysql_course
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_course`;
CREATE TABLE `t_mysql_course`  (
  `cid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程编号',
  `cname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程名称',
  `tid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师编号',
  PRIMARY KEY (`cid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '课程信息表' ROW_FORMAT = Dynamic;

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

-- ----------------------------
-- Table structure for t_mysql_score
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_score`;
CREATE TABLE `t_mysql_score`  (
  `sid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生编号，外键',
  `cid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程编号，外键',
  `score` float NULL DEFAULT 0 COMMENT '成绩',
  INDEX `sid`(`sid`) USING BTREE,
  INDEX `cid`(`cid`) USING BTREE,
  CONSTRAINT `t_mysql_score_ibfk_1` FOREIGN KEY (`sid`) REFERENCES `t_mysql_student` (`sid`) ON DELETE RESTRICT ON UPDATE RESTRICT,
  CONSTRAINT `t_mysql_score_ibfk_2` FOREIGN KEY (`cid`) REFERENCES `t_mysql_course` (`cid`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '成绩信息表' ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of t_mysql_score
-- ----------------------------
INSERT INTO `t_mysql_score` VALUES ('01', '01', 80);
INSERT INTO `t_mysql_score` VALUES ('01', '02', 90);
INSERT INTO `t_mysql_score` VALUES ('01', '03', 99);
INSERT INTO `t_mysql_score` VALUES ('02', '01', 70);
INSERT INTO `t_mysql_score` VALUES ('02', '02', 60);
INSERT INTO `t_mysql_score` VALUES ('02', '03', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '01', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '02', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '03', 80);
INSERT INTO `t_mysql_score` VALUES ('04', '01', 50);
INSERT INTO `t_mysql_score` VALUES ('04', '02', 30);
INSERT INTO `t_mysql_score` VALUES ('04', '03', 20);
INSERT INTO `t_mysql_score` VALUES ('05', '01', 76);
INSERT INTO `t_mysql_score` VALUES ('05', '02', 87);
INSERT INTO `t_mysql_score` VALUES ('06', '01', 31);
INSERT INTO `t_mysql_score` VALUES ('06', '03', 34);
INSERT INTO `t_mysql_score` VALUES ('07', '02', 89);
INSERT INTO `t_mysql_score` VALUES ('07', '03', 98);

-- ----------------------------
-- Table structure for t_mysql_student
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_student`;
CREATE TABLE `t_mysql_student`  (
  `sid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生编号',
  `sname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生名称',
  `sage` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生年龄',
  `ssex` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生性别',
  PRIMARY KEY (`sid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '学生信息表' ROW_FORMAT = Dynamic;

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

-- ----------------------------
-- Table structure for t_mysql_teacher
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_teacher`;
CREATE TABLE `t_mysql_teacher`  (
  `tid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师编号',
  `tname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师名称',
  PRIMARY KEY (`tid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '教师信息表' ROW_FORMAT = Dynamic;

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

SET FOREIGN_KEY_CHECKS = 1;