面试题整理：SQL（一）

1.横纵表转换

A表

Name	Course	Grade
Alex	English	80
Alex	Chinese	70
Alex	Japanese	85
Bob	English	75
Bob	Chinese	85
Bob	Japanese	80

B表

Name	English	Chinese	Japanese
Alex	80	70	85
Bob	75	85	80
Chris	90	70	60

 

 

 

 

 

 

 

A -> B

select Name, 
SUM(case Course when 'English' then Grade else 0 end) as English,
SUM(case Course when 'Chinese' then Grade else 0 end) as Chinese,
SUM(case Course when 'Japanese' then Grade else 0 end) as Japanese
from TranscriptA
group by Name

B -> A

select Name,'English' AS Course,English  AS Grade from TranscriptB
union all 
select Name,'Chinese' AS Course,Chinese AS Grade from TranscriptB 
union all 
select Name,'Japanese' AS Course,Japanese AS Grade from TranscriptB
order by Name,Course desc;

2.假设有学习成绩表

用一条SQL查出每一门成绩都大于80的学生的姓名

select distinct name from table where name not in (select distinct name from table where chengji <= 80)

select name from table group by name having min(chengji)>80

3.假设有Team表，只有一个Name字段，代表球队名字

用SQL查处各队之间互相比赛的组合

select a.name, b.name from team a, team b where a.name< b.name

4.统计工资累加

A表

Year	Salary
2010	1000
2011	1500
2012	2000
2013	2500

 

 

 

 

 

 

 

B表

Year	Salary
2010	1000
2011	2500
2012	4500
2013	7000

 

 

 

 

 

 

 

 

A -> B

select b.Year, sum(a.Salary) AccSalary from TA a, TA b
where a.Year <= b.Year
group by b.Year

select a.year, (select sum(b.Salary) from TA b 
where b.Year <= a.year) AccSalary 
from TA a

To be continue...