经典的SQL面试题

SQL中 inner join、 left join 、right join、 outer join之间的区别

A表(a1,b1,c1) B表(a2,b2)

a1 b1 c1 a2 b2

01 数学 95 01 张三

02 语文 90 02 李四

03 英语 80 04 王五

select A.*,B.* from A

inner join B on(A.a1=B.a2)

结果是：

a1 b1 c1 a2 b2

01 数学 95 01 张三

02 语文 90 02 李四

select A.*,B.* from A

left outer join B on(A.a1=B.a2)

结果是:

a1 b1 c1 a2 b2

01 数学 95 01 张三

02 语文 90 02 李四

03 英语 80 NULL NULL

select A.*,B.* from A

right outer join B on(A.a1=B.a2)

结果是:

a1 b1 c1 a2 b2

01 数学 95 01 张三

02 语文 90 02 李四

NULL NULL NULL 04 王五

select A.*,B.* from A

full outer join B on(A.a1=B.a2)

结果是:

a1 b1 c1 a2 b2

01 数学 95 01 张三

02 语文 90 02 李四

03 英语 80 NULL NULL

NULL NULL NULL 04 王五

Student(S#,Sname,Sage,Ssex) 学生表

Course(C#,Cname,T#) 课程表

SC(S#,C#,score) 成绩表

Teacher(T#,Tname) 教师表

问题：

1、查询“001”课程比“002”课程成绩高的所有学生的学号；

select a.S#

from (select s#,score from SC where C#=’001′) a,

(select s#,score from SC where C#=’002′) b

where a.score>b.score and a.s#=b.s#;

2、查询平均成绩大于60分的同学的学号和平均成绩；

select S#,avg(score)

from sc

group by S# having avg(score) >60;

3、查询所有同学的学号、姓名、选课数、总成绩；

select Student.S#,Student.Sname,count(SC.C#),sum(score)

from Student left Outer join SC on Student.S#=SC.S#

group by Student.S#,Sname

4、查询姓“李”的老师的个数；

select count(distinct(Tname))

from Teacher

where Tname like ‘李%’;

5、查询没学过“叶平”老师课的同学的学号、姓名；

select Student.S#,Student.Sname

from Student

where S# not in (select distinct( SC.S#) from SC,Course,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname=’叶平’);

6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；

select Student.S#,Student.Sname

from Student,SC

where Student.S#=SC.S# and SC.C#=’001′and exists( Select * from SC as SC_2 where SC_2.S#=SC.S# and SC_2.C#=’002′);

7、查询学过“叶平”老师所教的所有课的同学的学号、姓名；

select S#,Sname

from Student

where S# in

(select S#

from SC ,Course ,Teacher

where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname=’叶平’ group by S# having count(SC.C#)=(select count(C#) from Course,Teacher where Teacher.T#=Course.T# and Tname=’叶平’));

8、查询所有课程成绩小于60分的同学的学号、姓名；

select S#,Sname

from Student

where S# not in (select Student.S# from Student,SC where S.S#=SC.S# and score>60);

9、查询没有学全所有课的同学的学号、姓名；

select Student.S#,Student.Sname

from Student,SC

where Student.S#=SC.S#

group by Student.S#,Student.Sname having count(C#) <(select count(C#) from Course);

10、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名；

select S#,Sname

from Student,SC

where Student.S#=SC.S# and C# in （select C# from SC where S#='1001'）;

11、删除学习“叶平”老师课的SC表记录；

Delect SC

from course ,Teacher

where Course.C#=SC.C# and Course.T#= Teacher.T# and Tname='叶平';

12、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 L.C# 课程ID,L.score 最高分,R.score 最低分

FROM SC L ,SC R

WHERE L.C# = R.C#

and

L.score = (SELECT MAX(IL.score)

FROM SC IL,Student IM

WHERE IL.C# = L.C# and IM.S#=IL.S#

GROUP BY IL.C#)

and

R.Score = (SELECT MIN(IR.score)

FROM SC IR

WHERE IR.C# = R.C#

GROUP BY IR.C# );

13、查询学生平均成绩及其名次

SELECT 1+(SELECT COUNT( distinct 平均成绩)

FROM (SELECT S#,AVG(score) 平均成绩

FROM SC

GROUP BY S# ) T1

WHERE 平均成绩 > T2.平均成绩) 名次, S# 学生学号,平均成绩

FROM (SELECT S#,AVG(score) 平均成绩 FROM SC GROUP BY S# ) T2

ORDER BY 平均成绩 desc;

14、查询各科成绩前三名的记录:(不考虑成绩并列情况)

SELECT t1.S# as 学生ID,t1.C# as 课程ID,Score as 分数

FROM SC t1

WHERE score IN (SELECT TOP 3 score

FROM SC

WHERE t1.C#= C#

ORDER BY score DESC)

ORDER BY t1.C#;

15、查询每门功成绩最好的前两名

SELECT t1.S# as 学生ID,t1.C# as 课程ID,Score as 分数

FROM SC t1

WHERE score IN (SELECT TOP 2 score

FROM SC

WHERE t1.C#= C#

ORDER BY score DESC )

ORDER BY t1.C#;

补充：

已经知道原表

year salary

——————

2000 1000

2001 2000

2002 3000

2003 4000

解：

select b.year,sum(a.salary)

from salary a,salary b

where a.year<=b.year

group by b.year

order by b.year;

在面试过程中多次碰到一道SQL查询的题目，查询A(ID,Name)表中第31至40条记录，ID作为主键可能是不是连续增长的列，完整的查询语句如下：

方法一：

select top 10 *

from A

where ID >(select max(ID) from (select top 30 ID from A order by ID ) T) order by ID

方法二：

select top 10 *

from A

where ID not In (select top 30 ID from A order by ID)

order by ID