python学习之老男孩python全栈第九期_数据库day003 -- 作业

转载 于 2018-08-09 21:17:00 发布 · 99 阅读 · 0 ·
CC 4.0 BY-SA版权
原文链接：http://www.cnblogs.com/BlameKidd/p/9451809.html
文章标签：

#数据库 #python

本文通过具体实例，展示了如何利用SQL进行复杂的数据查询与分析，包括成绩筛选、数据汇总、关联查询等，为数据库操作提供了实用指南。

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 数据库：

class：

 course：

student：

teacher：

score：

 

 

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 50624
 Source Host           : localhost
 Source Database       : sqlexam

 Target Server Type    : MySQL
 Target Server Version : 50624
 File Encoding         : utf-8

 Date: 10/21/2016 06:46:46 AM
*/

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
--  Table structure for `class`
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `caption` varchar(32) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `class`
-- ----------------------------
BEGIN;
INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
COMMIT;

-- ----------------------------
--  Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `cname` varchar(32) NOT NULL,
  `teacher_id` int(11) NOT NULL,
  PRIMARY KEY (`cid`),
  KEY `fk_course_teacher` (`teacher_id`),
  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
COMMIT;

-- ----------------------------
--  Table structure for `score`
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) NOT NULL,
  `course_id` int(11) NOT NULL,
  `num` int(11) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_score_student` (`student_id`),
  KEY `fk_score_course` (`course_id`),
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `score`
-- ----------------------------
BEGIN;
INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
COMMIT;

-- ----------------------------
--  Table structure for `student`
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `gender` char(1) NOT NULL,
  `class_id` int(11) NOT NULL,
  `sname` varchar(32) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_class` (`class_id`),
  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `student`
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');
COMMIT;

-- ----------------------------
--  Table structure for `teacher`
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `tid` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) NOT NULL,
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `teacher`
-- ----------------------------
BEGIN;
INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;
表结构和数据

 

 

 

1. 成绩表中所有大于60分的数据

SELECT * from score where num>60;

 

 

 

2. 查询每个老师教多少门课

SELECT teacher_id,COUNT(cid) FROM course GROUP BY teacher_id;

 

3. 列出课程与对应老师

SELECT * FROM course LEFT JOIN teacher on course.teacher_id=teacher.tid;

 

4. 列出学生与对应班级

SELECT * FROM student LEFT JOIN class on student.class_id=class.cid;

 

5. 列出男生的个数和女生的个数

SELECT gender,COUNT(gender) from student GROUP BY gender;

 

6. 查询“生物”课程比“物理”课程成绩高的所有学生的学号

先拿到所有的生物成绩
SELECT score.sid,score.student_id,course.cname,score.num from score LEFT JOIN course ON score.course_id=course.cid WHERE course.cname='生物';
在拿到所有的物理成绩
SELECT score.sid,score.student_id,course.cname,score.num from score LEFT JOIN course ON score.course_id=course.cid WHERE course.cname='物理';
接着输出生物成绩大于物理成绩的数据
SELECT
    * 
FROM
    (
    SELECT
        score.sid,
        score.student_id,
        course.cname,
        score.num 
    FROM
        score
        LEFT JOIN course ON score.course_id = course.cid 
    WHERE
        course.cname = '生物' 
    ) AS A
    INNER JOIN (
    SELECT
        score.sid,
        score.student_id,
        course.cname,
        score.num 
    FROM
        score
        LEFT JOIN course ON score.course_id = course.cid 
    WHERE
        course.cname = '物理' 
    ) AS B ON A.student_id = B.student_id 
WHERE
    A.num > B.num;

最后，把* 改为A.student_id 即可
SELECT
    A.student_id 
FROM
    (
    SELECT
        score.sid,
        score.student_id,
        course.cname,
        score.num 
    FROM
        score
        LEFT JOIN course ON score.course_id = course.cid 
    WHERE
        course.cname = '生物' 
    ) AS A
    INNER JOIN (
    SELECT
        score.sid,
        score.student_id,
        course.cname,
        score.num 
    FROM
        score
        LEFT JOIN course ON score.course_id = course.cid 
    WHERE
        course.cname = '物理' 
    ) AS B ON A.student_id = B.student_id 
WHERE
    A.num > B.num;

 

 

7. 查询平均成绩大于60分的同学的学号、姓名和平均成绩 

select student_id,student.sname,avg(num) from score LEFT JOIN student ON score.student_id=student.sid GROUP BY student_id HAVING AVG(num)>60;

用临时表做：

SELECT B.student_id,student.sname,B.avg_num from (select student_id,avg(num) as avg_num from score GROUP BY student_id HAVING AVG(num)>60) as B LEFT join student on B.student_id=student.sid;

 

8. 查询所有同学的学号、姓名、选课数、总成绩

select student.sid,student.sname,COUNT(score.course_id),sum(score.num) from student LEFT JOIN score ON student.sid=score.student_id GROUP BY student.sid;

 

9. 查询姓“李”的老师的个数

select count(tid) from teacher where tname like '李%';

 

10. 查询没学过“李平”老师课的同学的学号、姓名

先查询选过李平老师课的学生ID
SELECT
    student_id 
FROM
    score 
WHERE
    course_id IN ( SELECT course.cid FROM teacher LEFT JOIN course ON teacher.tid = course.teacher_id WHERE teacher.tname = '李平老师' ) 
GROUP BY
    student_id

最后，从学生表里面选出没学过李平老师的课的数据
SELECT
    student.sid,
    student.sname 
FROM
    student 
WHERE
    sid NOT IN (
    SELECT
        student_id 
    FROM
        score 
    WHERE
        course_id IN ( SELECT course.cid FROM teacher LEFT JOIN course ON teacher.tid = course.teacher_id WHERE teacher.tname = '李平老师' ) 
    GROUP BY
    student_id 
    )

 

 

转载于:https://www.cnblogs.com/BlameKidd/p/9451809.html

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