MySQL(作业练习)

day59

参考：http://www.cnblogs.com/wupeiqi/p/5748496.html

现有数据库

/*
 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 ('', '三年二班'), ('', '三年三班'), ('', '一年二班'), ('', '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 ('', '生物', ''), ('', '物理', ''), ('', '体育', ''), ('', '美术', '');
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 ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', ''), ('', '', '', '');
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 ('', '男', '', '理解'), ('', '女', '', '钢蛋'), ('', '男', '', '张三'), ('', '男', '', '张一'), ('', '女', '', '张二'), ('', '男', '', '张四'), ('', '女', '', '铁锤'), ('', '男', '', '李三'), ('', '男', '', '李一'), ('', '女', '', '李二'), ('', '男', '', '李四'), ('', '女', '', '如花'), ('', '男', '', '刘三'), ('', '男', '', '刘一'), ('', '女', '', '刘二'), ('', '男', '', '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 ('', '张磊老师'), ('', '李平老师'), ('', '刘海燕老师'), ('', '朱云海老师'), ('', '李杰老师');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

表结构和数据

题目与答案：

第2题

#2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；

#先连表 课程和成绩
select * from score left join course on score.course_id = course.cid;

#选出生物的
select * from score left join course on score.course_id = course.cid where course.cname = "生物";

#从中选出课程id，学生id，课程及分数
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";

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";

#只能左右比较，所以 根据学生id左右连接 ，将生物与物理连接
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 #存在空不显示，
(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;

#根据条件进行选择
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 #存在空不显示，
(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;

#只要学号
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 #存在空不显示，
(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;

-- #选出有生物和物理的信息
-- select * from score left join course on score.course_id = course.cid where course.cname = "生物" or course.cname = "物理";
--
-- #从中选出课程id，学生id，课程及分数
-- 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" or course.cname = "物理";
-- 

第5题

#查询姓李的老师的个数
select count(tid) from teacher where tname like '李%'

第6题

#6、查询没学过“李平”老师课的同学的学号、姓名；

#先连接teacher和course
select * from course left join teacher on course.teacher_id = teacher.tid;

#挑出李平老师的课
select * from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师';

#选出其中的李平课程的id   2，4
select course.cid from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师';

#选择选过李平课的学生
select * from score where course_id in
(select course.cid from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师');

#选过李平课的学生ID
select student_id from score where course_id in
(select course.cid from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师')
group by student_id;

#到学生表中排除出以上ID
select * from student where sid not in
(
select student_id from score where course_id in
(select course.cid from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师')
group by student_id
);

#最终选出学号和姓名
select student.sid, student.sname from student where sid not in
(
select student_id from score where course_id in
(select course.cid from course left join teacher on course.teacher_id = teacher.tid where teacher.tname = '李平老师')
group by student_id
);

第7题

#7、查询学过“001”课程并且也学过编号“002”课程的同学的学号、姓名；

#选出学过 1和2 课程的学生信息
select * from score where course_id = 1 or course_id = 2 ;

#根据 学号进行分组
select student_id from score where course_id = 1 or course_id = 2 GROUP BY student_id having count(course_id)>1;#选了1或者2的课同学，大于2门课的说明是1和2都选了

#学生id已知, 匹配student名字
select student.sid,student.sname from
(select student_id from score where course_id = 1 or course_id = 2 GROUP BY student_id having count(course_id)>1) as A
left join student on A.student_id = student.sid;

第8题

#8、查询学过“李平”老师所教的所有课的同学的学号、姓名；

#先拿“李平"课程id  老师和课程先连表
select * from course left join teacher on teacher.tid = course.teacher_id;

#拿出课程id
select course.cid from course left join teacher on teacher.tid = course.teacher_id where teacher.tname = "李平老师";
#2,4

#根据2，4从score中选出学生信息
select * from score where course_id in
(select course.cid from course left join teacher on teacher.tid = course.teacher_id where teacher.tname = "李平老师");
#其中这些学生都选了李平的课

#选出李平的课都上的学生
select student_id from score where course_id in
(select course.cid from course left join teacher on teacher.tid = course.teacher_id where teacher.tname = "李平老师")
group by student_id having count(course_id) = (select count(course.cid) from course left join teacher on teacher.tid = course.teacher_id where teacher.tname = "李平老师");
#等于李老师的课程数量即为上了老师的所有课

第10题

#10、查询有课程成绩小于60分的同学的学号、姓名；

#找到有成绩小于60的学生
select * from score where num < 60;

#找到有成绩小于60的学生的id
select student_id from score where num < 60;

#并根据学号分组，因为有重复id出现，挂了多科的
select student_id from score where num < 60 GROUP BY student_id;
select distinct student_id from score where num < 60;#去重第二个方法

#和student进行连表
select student.sid, student.sname from (select student_id from score where num < 60 GROUP BY student_id) as A left join student on A.student_id = student.sid;

#第二个方法
select sid,sname from student where sid in (
        select distinct student_id from score where num < 60
    )

第11题

#11、查询没有学全所有课的同学的学号、姓名；

#获得课程总数
select count(cname) from course;
#select count(cid) from course;#主键速度更快

#每个学生id的上的课数, 如果不写 group by student_id会报错因为是根据学生id分组的
select student_id, count(course_id) as course_num from score group by student_id; 

#找出未选满的学生id
select student_id from
(select student_id, count(course_id) as course_num from score group by student_id) as A
where A.course_num not in (select count(cname) from course);

#对应名字
select sid,sname from student where sid in
(
select student_id from
(select student_id, count(course_id) as course_num from score group by student_id) as A
where A.course_num not in (select count(cname) from course)
);

第12题

#12、查询  至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；
#即和001一起上过课的

#选出了课程001号同学的课程id
select course_id from score where student_id = 1;

#选出和001号一起学习的ID
select DISTINCT student_id from score where course_id in (select course_id from score where student_id  = 1);

select sid, sname from (select DISTINCT student_id from score where student_id !=1 and course_id in (select course_id from score where student_id  = 1)) as A left join student on student.sid = A.student_id;
#还需排除自身