在Oracle 10g中将行值查询为不同的列

Question

嗨，大家好我有一张桌子，用于存储现场stu_score中不同主题的学生成绩。主题位于字段ex_subjects中，我需要查询表格，以便将得分排列为每个主题的单独列。我有管理查询数学，如：

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

输出

表格中的其他主题我需要相同的内容，例如ENGLISH，PHYSICS，CHEMISTRY ..... 解决这个问题的最佳方式是什么？

Answer 1

如果我理解你的查询，那么这可以在不改变你的数据库结构的情况下完成：

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

注意：我改变了顺序，因为在那种形式中它不再可用，现在它将得分相加，并按此排名。

但是，这种确切的数据库结构很糟糕。这不在First Normal Form (1NF)中，这会使事情变得不必要，并且容易出错。另外，请考虑阅读2NF，3NF和BCNF（其他也是如此，但AFAIK，这些是更广为人知和使用的普通形式）。我假设你正在学习，这将使你走上正确的轨道。

您应该将您的一个表分成（至少）两个：一个用于学生的个人数据（现在与MAIN别名一起使用的列），一个用于分数（其他列）。

Answer 2

对于只需要访问该表的查询，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