从多个列中的单个表中将多个行中的值检索到单个行中

Question

以下是我的问题的示例表：

数据库：MySql 5.1
表名：教育

id   edutype    university  subjects                    yearofpass    percentmarks

200  1          CBSE        Maths,Science,English,Hindi     2002          78.00 

200  2          CBSE        Maths,Physics,Chem,Biology      2004          68.00 

200  3          WBUT        Computer Science Engineering    2008          87.00 

100  1          ICSE        Maths,Science,English,Hindi     2001          72.00 

100  2          CBSE        Maths,Physics,Chem,Biology      2003          65.00 

100  3          NIT         Electronics Engineering         2008          75.00 

300  1          CBSE        Maths,Science,English,Hindi     2003          65.00 

300  2          CBSE        Maths,Physics,Chem,Biology      2005          63.00 

300  3          VIT         Metallurgy Engineering          2009          79.00 

现在我想运行一个sql查询，它将以下列格式输出结果：

id   uvr1  sub1                           yop1  pcm1   uvr2  sub2                            yop2  pcm2   uvr3   sub3                            yop3     pcm3

200  CBSE  Maths,Science,English,Hindi    2002  78.00  CBSE  Maths,Physics,Chem,Biology      2004  68.00  WBUT   Computer Science Engineering    2008     87.00 

100  ICSE  Maths,Science,English,Hindi    2001  72.00  CBSE  Maths,Physics,Chem,Biology      2003  65.00  NIT    Electronics Engineering         2008     75.00 

300  CBSE  Maths,Science,English,Hindi    2003  65.00  CBSE  Maths,Physics,Chem,Biology      2005  63.00  VIT    Metallurgy Engineering          2009     79.00 

如果您有任何好的方法可以分享，需要您的帮助。

先谢谢

Answer 1

您将尝试使用CONCAT和SUBSTRING函数并嵌套SELECT。 像：

SELECT SUBSTRING(CONCAT(subjects, 
(
SELECT subjects FROM education WHERE university=CBSE and rownum=2
)),0,27) 
FROM education WHERE university='CBSE' and rownum=1;

但这是非常糟糕和不确定的解决方案。在你的位置，我会尝试重新组织选择的要求。也许你提到这样的输出并不是必须的。

Answer 2

你可以试试这个：

SELECT 
    e1.id,
    e1.university as uvr1,
    e1.subjects as sub1,
    e1.yearofpass as yop1,
    e1.percentmarks as pcm1,
    e2.university as uvr2,
    e2.subjects as sub2,
    e2.yearofpass as yop2,
    e2.percentmarks as pcm2,
    e3.university as uvr3,
    e3.subjects as sub3,
    e3.yearofpass as yop3,
    e3.percentmarks as pcm3
FROM 
    Education as e1
LEFT JOIN Education as e2
    ON e1.id = e2.id
    AND e2.edutype = e1.edutype+1
LEFT JOIN Education as e3
    ON e1.id = e3.id
    AND e3.edutype = e1.edutype+2
WHERE
    e1.edutype = 1

但是......只有你拥有更多需要添加额外联接的大学才能拥有相同ID的3所大学。

另外看着你的表格结构我认为你应该阅读更多关于Database Normalization它可以帮助你的信息。

您可以这样做：

Answer 3

虽然在MySQL中完全可以使用以下形式的PIVOT TABLE查询，但在大多数情况下，像eggyal建议并在应用程序级别处理此类事情要好得多......

SELECT id
     , MAX(CASE WHEN edutype = 1 THEN university END) uvr1
     , MAX(CASE WHEN edutype=1 THEN subjects END) sub1 
  FROM education 
 GROUP 
    BY id;