sql - 结果以多行形式返回

Question

我创建了一个在每天结束时运行的存储过程，它将返回类(class)中每个学生的出勤百分比，结果集将显示学生之前的出勤百分比与新百分比的比较。但由于某种原因，结果存储在多行而不是一行中。下图将使您更好地理解问题。

两个表:

学生表

百分比表

我编写的用于将结果放入组合表中的代码:

select 
StudentTb.StudentId,
StudentTb.Forename,
StudentTb.Surname,
CONVERT(VARCHAR(10),DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE())-1, 0),103) as [Previous Reading Date]
case studentTb.Date 
when DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE())-1, 0) then PercentageTb.Percentage
End
'Previous Percentage'
CONVERT(VARCHAR,DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE()), 0),103) as [Present Reading Date]
case studentTb.Date 
when DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE())-1, 0) then PercentageTb.Percentage
End
'Current Percentage'
from studentTb inner join
                  PercentageTb on studentTb.StudentID = PercentageTb.StudentID

这是此查询的结果集!

但这不是我想要的结果，下面显示了所需的结果集!

我认为 CASE 语句可以为我做到这一点，但显然我错了，有人可以给我一些关于我需要从这里去哪里的指示吗？

Answer 1

为什么不直接用子选择来进行选择呢？假设一名学生每天只能得到一个结果

DECLARE @CurrentDate DATE
DECLARE @PreviousDate DATE
SET @CurrentDate = 
SET @PreviousDate = 


SELECT
    StudentTb.StudentId AS [ID],
    StudentTb.Forename AS [Forename],
    StudentTb.Surname AS [Surname],
    (SELECT Percentage from PercentageTb where StudentID = S.studentID and Date = @PreviousDate) AS [PreviousPercentage]
    (SELECT Percentage from PercentageTb where StudentID = S.studentID and Date = @CurrentDate) AS [CurrentPercentage]
from studentTb  AS S