在Oracle 10g中将行值作为不同列查询

Question

嗨，我有一张表，用于存储字段stu_score中不同主题的学生成绩。主题在字段ex_subjects中，我需要查询表格，以便将分数排列为每个主题的单独列。我已成功地查询数学喜欢：

select stu_number, stu_name, ex_name, stu_score as MATHEMATICS 
from EXAMS_MASTER_REGISTER 
where stu_level = '1' and stu_stream = 'EAST' 
and ex_semester = 'FIRST' 
and ex_name = 'MIDYEARS' 
and ex_subject = 'MATHEMATICS' 
and academic_year = '2012' 
order by stu_score desc 

的输出继电器是

我需要在表中的其他科目，如ENGLISH，PHYSICS，CHEMISTRY一样..... 解决这个问题的最佳方法是什么？

Answer 1

的查询，只需要表中的一个访问，请尝试：

select stu_number, 
     max(stu_name) stu_name, 
     ex_name, 
     max(case when ex_subject = 'MATHEMATICS' then stu_score end) as MATHEMATICS, 
     max(case when ex_subject = 'ENGLISH' then stu_score end) as ENGLISH, 
     max(case when ex_subject = 'PHYSICS' then stu_score end) as PHYSICS, 
     max(case when ex_subject = 'CHEMISTRY' then stu_score end) as CHEMISTRY 
from EXAMS_MASTER_REGISTER 
where stu_level = '1' and 
     stu_stream = 'EAST' and 
     ex_semester = 'FIRST' and 
     ex_name = 'MIDYEARS' and 
     academic_year = '2012' 
group by stu_number, ex_name 
order by sum(stu_score) desc 

Answer 2

如果我理解您的查询好，那么可以这样做而无需改变你的数据库结构：

select MAIN.stu_number, MAIN.stu_name, MAIN.ex_name, 
    MATHS.stu_score as MATHEMATICS, 
    ENGLISH.stu_score as ENGLISH, 
    PHYSICS.stu_score as PHYSICS, 
    CHEMISTRY.stu_score as CHEMISTRY 
from EXAMS_MASTER_REGISTER MAIN 
left join EXAMS_MASTER_REGISTER MATHS on MAIN.stu_number = MATHS.stu_number AND MATHS.ex_subject = 'MATHEMATICS' 
left join EXAMS_MASTER_REGISTER ENGLISH on MAIN.stu_number = ENGLISH.stu_number AND ENGLISH.ex_subject = 'ENGLISH' 
left join EXAMS_MASTER_REGISTER PHYSICS on MAIN.stu_number = PHYSICS.stu_number AND PHYSICS.ex_subject = 'PHYSICS' 
left join EXAMS_MASTER_REGISTER CHEMISTRY on MAIN.stu_number = CHEMISTRY.stu_number AND CHEMISTRY.ex_subject = 'CHEMISTRY' 
where MAIN.stu_level = '1' 
and MAIN.stu_stream = 'EAST' 
and MAIN.ex_semester = 'FIRST' 
and MAIN.ex_name = 'MIDYEARS' 
and MAIN.academic_year = '2012' 
order by (NVL(MATHS.stu_score,0) + NVL(ENGLISH.stu_score,0) + NVL(PHYSICS.stu_score,0) + NVL(CHEMISTRY.stu_score,0)) desc 

注：我用的顺序改变了，在这种形式是不再可用，现在这个总结分数，然后排名。

但是，这个确切的DB结构是不好的。这不是在First Normal Form (1NF)，这使事情不必要的困难，并容易出错。另外请考虑阅读2NF，3NF和BCNF（其他人也是，但AFAIK，这些是更广泛已知和使用的正常形式）。我假设你正在学习，这会让你走上正轨。

你应该把你的一个表分成（至少）两个：一个用于学生的个人数据（现在用于MAIN别名的列），另一个用于分数（其他列）。