Question

Newbie Postgresql（9.6.6）问题：）

我想创建一个视图，根据不同的条件将单个列拆分为多个列。

示例表

  Name    Score   Season  
 ------- ------- -------- 
  John       12   Fall    
  John       15   Winter  
  John       13   Spring  
  Sally      17   Fall    
  Sally      10   Winter  
  Sally      14   Spring  
  Henry      16   Fall    
  Henry      12   Winter  
  Henry      18   Spring

我希望View能够显示如下内容：

  Name    Fall Score   Winter Score   Spring Score  
 ------- ------------ -------------- -------------- 
  John            12             15             13  
  Sally           17             10             14  
  Henry           16             12             18

“Score”字段分为几个不同的列，每个列都基于引用“Season”字段的WHERE子句填充。我已经查看了Window Functions和CASE Statements来实现这个目的，但到目前为止还没有成功。

非常感谢任何帮助！

Answer 1

在loadComponent上进行分组，然后在Name列上有条件地SUM进行分组时，从整个表中进行选择将有效：

Score

您是否使用SELECT "Name", SUM(CASE WHEN "Season" = 'Fall' THEN "Score" ELSE 0 END) AS "Fall", SUM(CASE WHEN "Season" = 'Winter' THEN "Score" ELSE 0 END) AS "Winter", SUM(CASE WHEN "Season" = 'Spring' THEN "Score" ELSE 0 END) AS "Spring" FROM "mytable" GROUP BY "Name"取决于您以及数据的外观。如果每个（SUM()，Name）对有一行，那么Season将与SUM()

同等地工作

Answer 2

您需要一个数据透视表：

在SQL服务器上，您可以执行类似此示例的操作（希望它对于postgress是相同的），在其他版本的SQL中存在pivot关系运算符，但我不确定Pivot是否有效在Postgres

示例：

CREATE TABLE #Table
(
   Name nvarchar(400),
   Score int,
   Season nvarchar(400)
)

insert into #Table values ( 'John ',12,'Fall')
insert into #Table values ( 'John ',15,'Winter'   )
insert into #Table values ( 'John ',13,'Spring'   )
insert into #Table values ( 'Sally',17,'Fall   '  )
insert into #Table values ( 'Sally',10,'Winter'   )
insert into #Table values ( 'Sally',14,'Spring'   )
insert into #Table values ( 'Henry',16,'Fall'    ) 
insert into #Table values ( 'Henry',12,'Winter'   )
insert into #Table values ( 'Henry',18,'Spring'  )

select 
    c.Name
    ,sum(c.[Fall Score]) as [Fall Score]
    ,sum(c.[Winter Score]) as [Winter Score]
    ,sum(c.[Spring Score]) as [Spring Score]
from
(SELECT 
    t.name,
    case 
        when t.Season = 'Fall' then t.Score
        when t.Season = 'Winter' then 0
        when t.Season = 'Spring' then 0
    end as [Fall Score],
    case 
        when t.Season = 'Fall' then 0
        when t.Season = 'Winter' then t.Score
        when t.Season = 'Spring' then 0
    end as [Winter Score],
    case 
        when t.Season = 'Fall' then 0
        when t.Season = 'Winter' then 0
        when t.Season = 'Spring' then t.Score
    end as [Spring Score]
from #Table t
)as c 
group by c.name

SQL |根据条件将列视为多列

2 个答案: