Artículo anterior: Conceptos básicos de la base de datos MySql
base de datos
DataBase (base de datos), un almacén para almacenar datos.
Cliente de interfaz gráfica proporcionado por el propio o tercero (DBeaver, Mariadb)
Cree varias bases de datos en Mysql, cada una para un proyecto.
Se pueden crear varias tablas en cada base de datos y las tablas se utilizan para guardar un conjunto de datos.
Lenguaje de consulta de datos DQL SELECCIONE Un lenguaje para consultar datos en tablas.
Combate de base de datos Mysql - creación de base de datos - creación de tablas - buscar varias tablas
Tabla de estudiantes, tabla de maestros, tabla de currículo, tabla de puntajes, varios ejemplos de consultas 43
#使用库
use test_job;
/*查看表
*/
show tables;
-- 查看所有数据库 --
show databases;
create table teacher(
sno char(10) primary key,
name varchar(20)
);
show create table student ;
create table teacher(
tno char(10) primary key,
tname varchar(20)
);
show create table teacher;
create table course(
cno char(10),
cname varchar(20),
tno char(20)
);
#查看已有表
show tables;
show create table course;
create table score(
sno char(10),
cno char(10),
score double(4,2)
);
insert into student values('s001','张三',23,'男');
insert into student values('s002','赵美',24,'女');
insert into student values('s004','王五',22,'男');
insert into student values('s005','李军',22,'男');
insert into student values('s026','李军',21,'男');
commit;
insert into teacher values('t001','张老实');
insert into teacher values('t002','李二哈');
insert into teacher values ('t004', '刘阳');
insert into teacher values ('t023', '刘大');
insert into teacher values ('t005', '谌燕');
insert into teacher values ('t006', '胡明星');
insert into teacher values('t009','张帅');
insert into teacher values('t010','大卫');
insert into teacher values('t011','丽莎');
commit;
rename table t_job to test_job;
alter table teacher add gendar varchar(10);
show create table teacher ;
alter table teacher add test varchar(1) first;
alter table teacher add test2 int after sno;
alter table teacher drop test;
alter table teacher drop test2;
alter table teacher change gendar te int;
alter table teacher change sno tno varchar(10);
create table test(id int);
show create table test;
desc test;
desc teacher;
drop table test;
insert into course values ('c001','J2SE','t002');
insert into course values ('c002','Java Web','t002');
insert into course values ('c003','SSH','t001');
insert into course values ('c004','Oracle','t001');
insert into course values ('c005','SQL SERVER 2005','t003');
insert into course values ('c006','C#','t003');
insert into course values ('c007','JavaScript','t002');
insert into course values ('c008','DIV+CSS','t001');
insert into course values ('c009','PHP','t003');
insert into course values ('c010','EJB3.0','t002');
commit;
insert into score values('s001','c001',78.9);
insert into score values('s002','c001',90.0);
insert into score values ('s001','c001',78.9);
insert into score values ('s002','c001',80.9);
insert into score values ('s003','c001',81.9);
insert into score values ('s004','c001',60.9);
insert into score values ('s001','c002',82.9);
insert into score values ('s002','c002',72.9);
insert into score values ('s003','c002',81.9);
insert into score values ('s001','c003',59);
insert into score values('s006','c006',66);
insert into score values('s004','c006',78);
insert into score values('s002','c003',62);
commit;
desc score;
# 1、查询“c001”课程比“c002”课程成绩高的所有学生的学号；
select *from
(select * from score where cno = 'c001')a,
(select * from score where cno = 'c002')b
where a.sno = b.sno and a.score>b.score;
# 2、查询平均成绩大于60 分的同学的学号和平均成绩；
select sno,avg(score)
from score group by sno
having avg(score)>60;
#3、查询所有同学的学号、姓名、选课数、总成绩；
select b.sno,b.ss,b.cc,s.name from
(select * from student)s,
(select sno,sum(score) ss,count(cno) cc from score group by sno)b
where s.sno=b.sno;
#4、查询姓“刘”的老师的个数；
select count(*)
from teacher
where tname like '刘%';
#5、查询没学过“谌燕”老师课的同学的学号、姓名；
select stu.sno ,stu.name from student stu where sno not in(
select distinct s.sno from score s where s.cno in(
select cno from course c left join teacher t on c.tno=t.tno where t.tname='谌燕'));
# what is distinct?
#6、查询学过“c001”并且也学过编号“c002”课程的同学的学号、姓名；
select * from student where sno in (
select distinct a.sno from
(select * from score) a,
(select * from score) b
where a.cno ='c001' and b.cno = 'c002' and a.sno=b.sno
);
#what is left join
#7、查询学过“谌燕”老师所教的所有课的同学的学号、姓名；
select stu.sno , stu.name from student stu where sno in(
select distinct s.sno from score s where s.cno in(
select cno from course c left join teacher t on c.tno = t.tno where t.tname='谌燕'
)
)
#8、查询课程编号“c002”的成绩比课程编号“c001”课程低的所有同学的学号、姓名；
select s.sno , s.name from student s where sno in (
select distinct a.sno from
(select * from score) a,
(select * from score) b
where a.cno ='c001' and b.cno = 'c002' and a.sno=b.sno and a.score < b.score
);
#9、查询所有课程成绩小于60 分的同学的学号、姓名；
select s.sno ,s.name from student s where sno in(
select distinct a.sno from
(select * from score) a
where a.score < 60
)
#10、查询没有学全所有课的同学的学号、姓名；]
select s.sno,s.name,count(s1.cno)from student s
join (select * from score) s1
on s.sno=s1.sno group by s.sno,s.name having count(s1.cno)<(select count(cno)from course);
#11、查询至少有一门课与学号为“s001”的同学所学相同的同学的学号和姓名；
select s.sno ,s.name from student s where sno in (
select sno from(
select sno from score where cno in(
select cno from score where sno='s001')
) t where t.sno<>'s001'
)
#12、查询至少学过学号为“s001”同学所有一门课的其他同学学号和姓名；
select * from score sc
left join student st
on st.sno=sc.sno
where sc.sno<>'s001'and sc.cno in(select cno from score where sno='s001')
#13、把“SC”表中“谌燕”老师教的课的成绩都更改为此课程的平均成绩；
#平均成绩的值
select avg(c1.score) from score c1
where c1.cno in(select cno from course a,teacher b where a.tno=b.tno and b.tname='谌燕');
#更新无效
update score c1 set c1.score=(select avg(c1.score) score from teacher t,course c where t.tno=c.tno and t.tname='谌燕' and c1.cno=c.cno group by c1.cno)
where c1.cno in(select cno from course a,teacher b where a.tno=b.tno and b.tname='谌燕');
#14、查询和“s001”号的同学学习的课程完全相同的其他同学学号和姓名；
#输出学号
select * from score s1
where sno<>'s001'and cno in (select cno from score where sno='s001')
group by sno having count(s1.cno)=(select count(*) from score where sno='s001');
#15、删除学习“谌燕”老师课的SC 表记录；
#有效
delete from score where score.cno in(
select cno from course c
left join teacher t on c.tno = t.tno
where t.tname = '谌燕'
)
#16、向SC 表中插入一些记录，这些记录要求符合以下条件：没有上过编号“c002”课程的同学学号、“c002”号课的平均成绩；
#有效
insert into score(sno,cno,score)
select distinct s1.sno,s.cno,(select avg(score) from score where cno='c002') from student s1,score s where s1.sno not in(
select sno from score s2 where s1.sno=s2.sno and cno='c002'
)and s.cno='c002';
#what is group by
#17、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
select cno 课程ID ,max(score) 最高分,min(score)最低分 from score group by cno;
#18、按各科平均成绩从低到高和及格率的百分数从高到低顺序
select cno,avg(score),sum(case when score>=60 then 1 else 0 end)/count(*) as 及格率
from score group by cno
order by avg(score) , 及格率 desc
#19、查询不同老师所教不同课程平均分从高到低显示
select t.tno,c.cno,avg(score) from score sc, course c,teacher t
where sc.cno=c.cno and c.tno=t.tno
group by c.cno
order by avg(score) desc
#20、统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]
#无效
select sc.cno,c.cname,
sum(case when score between 85 and 100 then 1 else 0 end) AS '[100-85]',
sum(case when score between 70 and 85 then 1 else 0 end) AS "[85-70]",
sum(case when score between 60 and 70 then 1 else 0 end) AS "[70-60]",
sum(case when score <60 then 1 else 0 end) AS "[<60]"
from score sc, course c
where sc.cno=c.cno
group by sc.cno ,c.cname;
#21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
#无效
select * from score (select sno,cno,score
row_number() over (partition by cno order by score desc) rn from score
) where rn<4
#22、查询每门课程被选修的学生数
select cno ,count(sno) from score group by cno;
#23、查询出只选修了一门课程的全部学生的学号和姓名
select s.sno, s.name, count(s1.cno) from student s
left join score s1
on s1.sno = s.sno group by s.name ,s1.sno having count(cno)=1
#24、查询男生、女生人数
select sex ,count(*) from student group by sex
#25、查询姓“张”的学生名单
select * from student s where s.name like '张%'
#26、查询同名同性学生名单，并统计同名人数
select s.name , count(*) from student s group by s.name having count(*)>1
#27、1981 年出生的学生名单(注：Student 表中Sage 列的类型是number)
#select * from student t where to char(sysdate,'yyyy')-sage =1981
#28、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列
select cno,avg(score) from score group by cno order by avg(score)asc,cno desc;
#29、查询平均成绩大于85 的所有学生的学号、姓名和平均成绩
select st.sno,st.name,avg(score) from student st
left join score s1
on s1.sno=st.sno
group by st.sno,st.name having avg(s1.score)>80;
#30、查询课程名称为“数据库”，且分数低于60 的学生姓名和分数
select st.name,s1.score from student st,score s1,course c
where st.sno=s1.sno and s1.cno=c.cno and c.cname='J2SE' and s1.score<80
#31、查询所有学生的选课情况；
select st.sno, st.name ,c.cname from student st,score sc, course c
where sc.sno=st.sno and sc.cno = c.cno
#32、查询任何一门课程成绩在70 分以上的姓名、课程名称和分数；
select st.sno, st.name ,c.cname, sc.score from student st,score sc, course c
where sc.sno=st.sno and sc.cno = c.cno and sc.score>70
#33、查询不及格的课程，并按课程号从大到小排列
select sc.sno,c.cname,sc.score from score sc,course c
where sc.cno=c.cno and sc.score<70
order by sc.cno desc;
#34、查询课程编号为c001 且课程成绩在80 分以上的学生的学号和姓名；
select s.sno ,s.name , sc.score from student s ,score sc
where sc.sno = s.sno and sc.cno = 'c001' and sc.score >80
#35、求选了课程的学生人数
select count(sno) from score;
#36、查询选修“谌燕”老师所授课程的学生中，成绩最高的学生姓名及其成绩
select st.name,sc.score ,c.cname from student st,score sc ,course c,teacher t
where st.sno=sc.sno and sc.cno=c.cno and c.tno=t.tno and t.tname='李二哈'
and sc.score=(select max(score) from score where sc.cno=c.cno)
#37、查询各个课程及相应的选修人数
select sc.cno,count(sc.sno) from score sc group by sc.cno
#38、查询不同课程成绩相同的学生的学号、课程号、学生成绩
select a.* from score a ,score b where a.score=b.score and a.cno<>b.cno
# what is partition
#39、查询每门功课成绩最好的前两名
#无效
select * from (
select sno,cno,score, row_number() over(partition by cno order by score desc) my_rn from score t)
where my_rn<=1
#40、统计每门课程的学生选修人数（超过10 人的课程才统计）。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 cno,count(sno) from score group by cno
having count(sno)>2
order by count(sno) desc,cno asc;
#41、检索至少选修两门课程的学生学号
select sno from score group by sno
having count(sno)>1
#42、查询全部学生都选修的课程的课程号和课程名
select distinct(c.cno),c.cname from course c ,score sc
where sc.cno=c.cno
#43、查询没学过“谌燕”老师讲授的任一门课程的学生姓名
select st.name from student st
where st.sno not in
(select distinct sc.sno from score sc,course c,teacher t
where sc.cno=c.cno and c.tno=t.tno and t.tname='谌燕')
#44、查询两门以上不及格课程的同学的学号及其平均成绩
select sno,avg(score)from score
where sno in(select sno from score sc where sc.score<80
group by sno having count(sno)>1)
group by sno
#45、检索“c004”课程分数小于60，按分数降序排列的同学学号
select sno ,score from score where cno='c001'and score<90 order by score desc;
#46、删除“s002”同学的“c001”课程的成绩
delete from score where sno='s002' and cno='c001';Crea valor, disfruta compartiendo