MySql Group by 与 Pivot

Posted 2023-03-24

【中文标题】MySql Group by 与 Pivot

【英文标题】：MySql Group by with Pivot

【发布时间】：2014-09-30 12:48:32

【问题描述】：

我在 mysql 中有一个表（比如 studentinfo）。

SELECT * FROM StudentInfo;

我想要以下输出而不使用任何额外或临时表。 （可能正在使用 group by 和 pivot）

【问题讨论】：

你尝试过什么来达到你想要的输出？尝试修改您的问题。

我很困惑将 group by 和 pivot 结合起来，我自己就卡在那里了。

【参考方案1】：

你需要创建一个数据透视表，这里有一个link，里面有很多很好的例子。

基本上，你会做这样的事情

 SELECT Rollnumber, 
        property
      CASE WHEN Property="Name" then Property end as Name,
      CASE WHEN Property="Year" then Property end as Year,
      CASE WHEN Property="City" then Property end as City,
 FROM whatever_table
 GROUP BY Rollnumber

您可以随意修改它，以获得您想要的结果。

【参考方案2】：

这应该做你想做的：

select si.Rollnumber, 
       max(case when si.Property = 'Name' then si.Value end) as Name,
       max(case when si.Property = 'Year' then si.Value end) as Year,
       max(case when si.Property = 'City' then si.Value end) as City
from StudentInfo si
group by si.Rollnumber;

【参考方案3】：

试试下面：

      select * from (SELECT A.Rollnumber,if(A.Property='Name',Value,
        (select B.Value from StudentInfo B where B.Property='Name' and B.Rollnumber=A.Rollnumber LIMIT 1)) as Name,
        if(Property='Year',Value,
        (select B.Value from StudentInfo B where B.Property='Year' and B.Rollnumber=A.Rollnumber LIMIT 1)) as Year,
       if(Property='City',Value,
        (select B.Value from StudentInfo B where B.Property='City' and B.Rollnumber=A.Rollnumber LIMIT 1)) 
         as City 
         FROM StudentInfo A) Temp group by Rollnumber

【参考方案4】：

SELECT
    name.rollnumber,
    name.value AS name,
    year.value AS year,
    city.value AS city
FROM 
    StudentInfo name
    INNER JOIN StudentInfo year ON name.rollnumber = year.rollnumber
    INNER JOIN StudentInfo city ON name.rollnumber = city.rollnumber    
WHERE
    name.property = 'name' AND
    year.property = 'year' AND
    city.property = 'city' AND