MySQL面試題 數據庫MySQL經典面試題之SQL語句

1.根據emp數據表編寫SQL查出所有name重復的記錄且按照age降序。

+--------+--------+-----+

| emp_no | name   | age |

+--------+--------+-----+

|   1001 | 小明   |  18 |

|   1002 | 王強   |  20 |

|   1003 | 小雪   |  20 |

|   1004 | 小明   |  19 |

+--------+--------+-----+

 

select emp_no, name,age 
from emp 
where name in (
    select t.name from
     (    select name,count(name) as num 
         from emp 
         group by name 
         having num > 1
     )t
) 
order by age desc;

 

 （測試數據添加SQL見文章末尾）

1.學生表
Student(SID,Sname,Sage,Ssex) --SID 學生編號,Sname 學生姓名,Sage 出生年月,Ssex 學生性別

2.課程表
Course(CID,Cname,TID) --CID --課程編號,Cname 課程名稱,TID 教師編號
3.教師表
Teacher(TID,Tname) --TID 教師編號,Tname 教師姓名
4.成績表
SC(SID,CID,score) --SID 學生編號,CID 課程編號,score 分數

 

1. 平均成績及格了的學生

select avg(score) avg_score,SID 
from SC 
group by SID 
having avg_score >= 60;

2. 查詢平均成績大於等於60分的同學的學生編號和學生姓名和平均成績

select a.SID,a.Sname,b.avg_score from Student a join  
(
    select avg(score) avg_score,SID 
    from SC 
    group by SID 
    having avg_score >= 60
) b on a.SID = b.SID;

3. 查詢學過"張三"老師授課的同學的信息

select distinct a.SId,a.Sname,a.Sage,a.Ssex
from Student a
join SC b on a.SID = b.SID
join Course c on c.CID = b.CID
join Teacher d on d.TID = c.TID
where d.Tname = '張三';

 

4. 查詢學過編號為"01"並且也學過編號為"02"的課程的同學的信息 

 --方法1

select m.* 
from Student m 
where SID in
(
    select SID from
    (
        select distinct SID from SC where CID = '01'
        union all
        select distinct SID from SC where CID = '02'
    ) t 
    group by SID 
    having count(1) = 2
)
order by m.SID

  --方法2

select Student.* 
from Student 
join SC on Student.SID = SC.SID
where CID = '02' 
and exists (select 1 from SC sc_2 where sc_2.SID = SC.SID and sc_2.CID='01');

  --方法3

select Student.* 
from Student 
join SC on Student.SID = SC.SID
where CID = '01' 
and exists (select 1 from SC sc_2 where sc_2.SID = SC.SID and sc_2.CID='02');

 

5. 查詢學過編號為"01"但是沒有學過編號為"02"的課程的同學的信息

select Student.* from Student 
join SC on Student.SID = SC.SID where CID = '01' 
and not exists (select 1 from SC sc_2 where sc_2.SID = SC.SID and sc_2.CID='02');

 

 

6. 查詢兩門及其以上不及格課程的同學的學號

select SID from SC where score < 60 group by SID having count(1) >= 2;

 

7. 查詢兩門及其以上不及格課程的同學的學號、姓名及其平均成績

select Student.SID,Student.sname,avg(SC.score) as avg_score
from student join SC on student.SID = SC.SID
where Student.SID in(select SID from SC where score < 60 group by SID having count(1) >= 2) 
group by Student.SID,Student.sname;

 

查詢沒有學全所有課程的同學的信息

select Student.*
from Student left join SC
on Student.SID = SC.SID
group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

 

 

 

 

 

 

 

 

附錄》添加測試數據

1.學生表
create table Student(SID varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10));
insert into Student values('01' , '趙雷' , '1990-01-01' , '男');
insert into Student values('02' , '錢電' , '1990-12-21' , '男');
insert into Student values('03' , '孫風' , '1990-05-20' , '男');
insert into Student values('04' , '李雲' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吳蘭' , '1992-03-01' , '女');
insert into Student values('07' , '鄭竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');

2.課程表
create table Course(CID varchar(10),Cname nvarchar(10),TID varchar(10));
insert into Course values('01' , '語文' , '02');
insert into Course values('02' , '數學' , '01');
insert into Course values('03' , '英語' , '03');

3.教師表
create table Teacher(TID varchar(10),Tname nvarchar(10));
insert into Teacher values('01' , '張三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

4.成績表
create table SC(SID varchar(10),CID varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);