MySql Group with Pivot

Question

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）

Answer 1

您需要创建一个数据透视表，这里有一个link，其中有很多很好的例子。

基本上，你只是要做这样的事情

 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

您可以根据需要修改此项，以获得所需的结果。

Answer 2

这应该做你想要的：

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;

Answer 3

尝试以下：

      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

Answer 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