我们如何在Select Statement中使用案例？

Question

有没有办法在SQL中有条件地打印列？让我们说Select FirstName, LastName, RollNumber, Subject, Marks From Student给出了5柱FirstName, LastName, RollNumber, Subject, Marks的输出。它也接受一个参数@NameType。如果@NameType = 'First'然后输出应该只有FirstName, RollNumber, Subject, Marks。同样，如果@NameType = 'Second'然后输出应该只有SecondName, RollNumber, Subject, Marks排除列FirstName。如何实现这一目标？

Declare @NameType nvarchar(max);

Set @NameType='First'

Select FirstName, LastName, RollNumber, Subject, Marks From Student

Answer 1

DECLARE @NameType VARCHAR(10)
SET @NameType = 'First';

SELECT CASE WHEN @NameType = 'First' THEN FirstName
            WHEN @NameType = 'Second' THEN LastName END as [Name]
,RollNumber
,Subject
,Marks
FROM Student;

Answer 2

听起来像你的追随者：

DECLARE @NameType varchar(6); --no reason to be a `MAX`, Second is only 6 characters long,
                              --and it doesn't need to be an nvarchar, as neither string contains unicode characters
SET @NameType = 'First';
SELECT CASE @NameType WHEN 'First' THEN FirstName
                      WHEN 'Second' THEN LastName
       END AS [Name],
       RollNumber,
       Subject,
       Marks
FROM Student;

Answer 3

select
case when @NameType = 'First' then FirstName
     when @NameType = 'Second' then SecondName end ColName,
RollNumber, Subject, Marks From Student