子查询

create database one20210611 default charset=utf8;

use one20210611;
CREATE TABLE studentinfo (
StudentID char(10) DEFAULT NULL,
StudentName varchar(20) DEFAULT NULL,
Gender varchar(2) DEFAULT NULL,
Birthday date DEFAULT NULL,
ClassID int(4) DEFAULT NULL,
BeginYear year(4) DEFAULT NULL,
Phone varchar(11) DEFAULT NULL,
Province varchar(20) DEFAULT NULL,
City varchar(20) DEFAULT NULL,
Email varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

create table teacher (
id int,
teachername VARCHAR(10),
hiredate DATE,
gender char

);

create table classinfo (
id int, # 班级编号
classname varchar(10),
gradeid int, # 年级编号
beginyear varchar(10) # 开始年份

);

create table subject (
id int ,
subjectname varchar(10),
teacherid int

);

create table exam (
id int,
exam int,
subjectid int,
studentid int,
remark varchar(10) # 备注
);

create table grade(
id int ,
gradename varchar(10),
major varchar(20)
);

INSERT INTO one20210611.classinfo(id, classname, gradeid, beginyear) VALUES (2001, '20级1班', 20, '2020');
INSERT INTO one20210611.classinfo(id, classname, gradeid, beginyear) VALUES (2002, '20级2班', 20, '2020');

INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (1, 98, 101, 1, '无');
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (2, 89, 102, 1, NULL);
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (3, 79, 103, 1, '');
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (4, 96, 104, 1, NULL);
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (5, 85, 101, 2, NULL);
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (6, 89, 102, 2, NULL);
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (7, 79, 103, 2, NULL);
INSERT INTO one20210611.exam(id, exam, subjectid, studentid, remark) VALUES (8, 83, 104, 2, NULL);

INSERT INTO one20210611.grade(id, gradename, major) VALUES (20, '20级', '软件技术');

INSERT INTO one20210611.studentinfo(StudentID, StudentName, Gender, Birthday, ClassID, BeginYear, Phone, Province, City, Email) VALUES ('1', '张无忌', '男', '2021-06-10', 2001, 2020, '13012340001', '河南', '许昌', 'zwj@qq.com');
INSERT INTO one20210611.studentinfo(StudentID, StudentName, Gender, Birthday, ClassID, BeginYear, Phone, Province, City, Email) VALUES ('2', '张铁牛', '男', '2021-06-16', 2001, 2020, '13012340002', '河南', '许昌', 'ztn@qq.com');
INSERT INTO one20210611.studentinfo(StudentID, StudentName, Gender, Birthday, ClassID, BeginYear, Phone, Province, City, Email) VALUES ('3', '林平之', '男', '2021-06-15', 2001, 2020, '13012340003', '河南', '安阳', 'lpz@qq.com');
INSERT INTO one20210611.studentinfo(StudentID, StudentName, Gender, Birthday, ClassID, BeginYear, Phone, Province, City, Email) VALUES ('4', '令狐冲', '男', '2021-06-08', 2002, 2019, '13012340004', '河南', '濮阳', 'lhc@qq.com');
INSERT INTO one20210611.studentinfo(StudentID, StudentName, Gender, Birthday, ClassID, BeginYear, Phone, Province, City, Email) VALUES ('5', '岳灵珊', '女', '2021-06-02', 2002, 2019, '13012340005', '河南', '南阳', 'yls@qq.com');

INSERT INTO one20210611.subject(id, subjectname, teacherid) VALUES (101, 'mysql', 201);
INSERT INTO one20210611.subject(id, subjectname, teacherid) VALUES (102, 'java基础', 201);
INSERT INTO one20210611.subject(id, subjectname, teacherid) VALUES (103, '面向对象', 202);
INSERT INTO one20210611.subject(id, subjectname, teacherid) VALUES (104, '网页设计', 202);

INSERT INTO one20210611.teacher(id, teachername, hiredate, gender) VALUES (201, 'hys', '2021-06-04', '男');
INSERT INTO one20210611.teacher(id, teachername, hiredate, gender) VALUES (202, 'dj', '2021-06-01', '女');

-- 子查询 用子查询实现，查询出学生“林平之”的同班同学

1 找到林平之 的班级

2 查同班同学

select classid from studentinfo where studentname='林平之';

select * from studentinfo where classid=(select classid from studentinfo where studentname='林平之');

-- 查询《mysql》考试成绩刚好等于85分的学生名单
-- 1 需要查询学生名单 在studentinfo
-- 2 科目是mysql 在subject表中id
-- 3 成绩为90 在exam表中subjectid studentid

select studentname from studentinfo inner join exam on studentinfo.studentid=exam.studentid inner join subject on subject.id=exam.subjectid where subject.subjectname='mysql' and exam.exam=85;

select studentname from studentinfo, exam ,subject
where studentinfo.studentid=exam.studentid and subject.id=exam.subjectid and subject.subjectname='mysql' and exam.exam=85;

-- 查询《mysql》考试成绩刚好等于85分的学生名单 子查询

根据学生id 查询学生的名单

select studentname from studentinfo where studentid=2;

在成绩中找到成绩为85的学生id

select studentid from exam where exam=85;

在课程表中找到mysql的课程id

select id from subject where subjectname='mysql' ;
-- 融合
select studentname from studentinfo where studentid=(select studentid from exam where exam=85 and exam.subjectid=(select id from subject where subjectname='mysql'));

-- 更新“dj”的“网页设计”成绩为+5分

-- 找到__成绩 +5分 exam id subjectid studentid
update exam set exam =exam + 5 where subjectid=?
-- 找到mysql课程的id subject id subjectname
select id from subject where subjectname="网页设计";
-- 根据名字找id teacher
select id from teacher where teachername="dj";
-- 融合
update exam set exam =exam+5 where subjectid=(select id from subject where subjectname="网页设计" and subject.teacherid=(select id from teacher where teachername="dj"));

-- 删除"张无忌"的所有考试成绩
-- 1 在studentinfo表中找到张无忌的学生id
select studentid from studentinfo where studentname="张无忌";
-- 2 根据id在exam表中删除数据
delete from exam where studentid=?

-- 合并
delete from exam where studentid=(select studentid from studentinfo where studentname="张无忌");

-- 插入的子查询 把查询的结果作为内容 插入到新的数据
insert into studentinfo (select * from studentinfo where studentid=5);

-- 查询《mysql》考试成绩刚好等于85分的学生名单 in的使用 在...范围之内

根据学生id查询学生的名单

select studentname from studentinfo where studentid=?

在成绩中找到成绩为85的学生id

select studentid from exam where exam=85;

在课程中找到mysql的课程id

select id from subject where subjectname='mysql';
-- 融合
select studentname from studentinfo where studentid in (select studentid from exam where exam=85 and subjectid in (select id from subject where subjectname='mysql') );

-- 查询成绩表中科目编号为102的考试成绩中是否存在不及格的学生，如果存在不及格的学生就将参加科目编号102考试的学生编号和成绩全部查询显示出来
-- 是否存在不及格的学生
select studentid from exam where exam<60
-- 参加科目编号102考试的学生
where subjectid=102
-- 学生编号和成绩全部查询显示出来
select studentid,exam, from exam where?
-- 合并
select studentid,exam from exam where subjectid=102 and exists (select studentid from exam where exam<60);

-- 查询成绩比科目编号为"101"的这门课程的所有成绩都大的学生考试成绩
-- 1 查询__学生考试信息
select * from exam where where ?
-- 2 成绩比科目编号为"101"的这门课程的所有成绩都大
all(select exam from exam where subjectid =101)
-- 合并
select * from exam where exam > all(select exam from exam where subjectid =101); -- 比所有的成绩都要大

-- 查询成绩比科目编号为"101"的任意一个成绩都大的考试成绩
-- 1 查询__学生考试信息
select * from exam where where ?
-- 2 成绩比科目编号为"101"的这门课程的所有成绩都大
all(select exam from exam where subjectid =1)
-- 合并
select * from exam where exam > any(select exam from exam where subjectid =101);

select * from exam where exam > some(select exam from exam where subjectid =101);

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