sql面试题：问题1:查询每个同学的学生编号、学生姓名、选课总数...问题2：查询“张三”老师所授课程的学生中，成绩最高的学生信息...

以下内容是本人自己写的，并没有找到此题的官方解答，如有更好的解题过程，请不吝赐教

详细问题描述

解答

第一问

完整答案

SELECT 
student.s_id,student.s_name,COUNT(score.c_id),IF(SUM(score.`s_score`) IS NULL,0,SUM(score.`s_score`))
FROM student LEFT JOIN score ON student.`s_id` = score.`s_id`   GROUP BY student.s_id 

效果

第二问

完整答案

SELECT * FROM student JOIN score ON student.`s_id`=score.`s_id` JOIN course ON score.`c_id` = course.`c_id` 
WHERE (score.`c_id`,score.`s_score`) IN (
		SELECT c_id,MAX(s_score) AS s_score FROM score WHERE c_id IN (
			SELECT c_id FROM course WHERE t_id = (SELECT t_id FROM teacher WHERE t_name= "张三") 
		) GROUP BY c_id
	)

效果（有门课有两个最高成绩的学生）

第二问步骤描述

• 步骤一（查找这个老师所带课程的id和此课程最高成绩）

		SELECT c_id,MAX(s_score) AS s_score FROM score WHERE c_id IN (
			SELECT c_id FROM course WHERE t_id = (SELECT t_id FROM teacher WHERE t_name= "张三") 
		) GROUP BY c_id

效果展示

• 步骤二（将所需要的信息表关联）

SELECT * FROM student JOIN score ON student.`s_id`=score.`s_id` JOIN course ON score.`c_id` = course.`c_id`

效果展示

• 步骤三（要注意in的字段）

WHERE (score.`c_id`,score.`s_score`) in  (步驟一的結果)

附件sql表

/*
SQLyog Ultimate v12.09 (64 bit)
MySQL - 5.7.29-log : Database - review
*********************************************************************
*/


/*!40101 SET NAMES utf8 */;

/*!40101 SET SQL_MODE=''*/;

/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
CREATE DATABASE /*!32312 IF NOT EXISTS*/`review` /*!40100 DEFAULT CHARACTER SET utf8 */;

USE `review`;

/*Table structure for table `course` */

DROP TABLE IF EXISTS `course`;

CREATE TABLE `course` (
  `c_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `c_name` varchar(255) NOT NULL,
  `t_id` int(10) unsigned NOT NULL,
  PRIMARY KEY (`c_id`),
  KEY `t_id` (`t_id`),
  CONSTRAINT `course_ibfk_1` FOREIGN KEY (`t_id`) REFERENCES `teacher` (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

/*Data for the table `course` */

insert  into `course`(`c_id`,`c_name`,`t_id`) values (1,'语文',1),(2,'编译原理',2),(3,'Linux',3),(4,'数学',1);

/*Table structure for table `score` */

DROP TABLE IF EXISTS `score`;

CREATE TABLE `score` (
  `s_id` int(10) unsigned NOT NULL,
  `c_id` int(10) unsigned NOT NULL,
  `s_score` int(10) unsigned NOT NULL,
  KEY `s_id` (`s_id`),
  KEY `c_id` (`c_id`),
  CONSTRAINT `score_ibfk_1` FOREIGN KEY (`s_id`) REFERENCES `student` (`s_id`),
  CONSTRAINT `score_ibfk_2` FOREIGN KEY (`c_id`) REFERENCES `course` (`c_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `score` */

insert  into `score`(`s_id`,`c_id`,`s_score`) values (1,1,80),(2,1,80),(3,1,60),(7,1,50),(1,2,81),(2,2,71),(3,2,61),(7,2,51),(1,4,82),(2,4,72),(3,4,62),(7,4,52);

/*Table structure for table `student` */

DROP TABLE IF EXISTS `student`;

CREATE TABLE `student` (
  `s_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `s_name` varchar(255) NOT NULL,
  `s_birth` datetime NOT NULL,
  `s_sex` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`s_id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

/*Data for the table `student` */

insert  into `student`(`s_id`,`s_name`,`s_birth`,`s_sex`) values (1,'马云','2020-07-08 09:47:50','男'),(2,'孙传明','2020-07-08 09:48:08','男'),(3,'臧山松','2020-07-08 09:48:47','男'),(4,'贾小明','2020-07-08 09:49:02','男'),(5,'徐海露','2020-07-08 09:49:16','女'),(6,'尤路英','2020-07-08 09:49:36','女'),(7,'胡吃海塞','2020-07-08 09:49:56','男');

/*Table structure for table `teacher` */

DROP TABLE IF EXISTS `teacher`;

CREATE TABLE `teacher` (
  `t_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `t_name` varchar(255) NOT NULL,
  PRIMARY KEY (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

/*Data for the table `teacher` */

insert  into `teacher`(`t_id`,`t_name`) values (1,'张三'),(2,'李华'),(3,'牛宝丽');

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;