带别名的案例功能

Question

我希望将 CASE 语句与一个由两列的商产生的别名一起使用。我写的代码如下，但是 returns 出错了。谁能帮我解决这个问题？

SELECT TOP 5(ROUND(Registered_Students/Total_Student * 100,2)) AS Porcentaje, C.Total_Student, C.Registered_Students, S.Subject_Name, DATEPART(Year, C.Date) AS Año,
    CASE WHEN Porcentaje >= 75 THEN 'Elected'
         WHEN Porcentaje >= 50 THEN 'Elected 1'
         ELSE 'Not elected' AS Elections
FROM Cohort AS C
INNER JOIN Subject AS S
ON S.Id_Subject = C.Id_Subject
ORDER BY Porcentaje

Answer 1

你必须插入这个词； 'END'行尾

SELECT C.Total_Student, C.Registered_Students, S.Subject_Name, DATEPART(Year, C.Date) AS Año,
    CASE WHEN Porcentaje >= 75 THEN 'Elected'
         WHEN Porcentaje >= 50 THEN 'Elected 1'
         ELSE 'Not elected' END AS Elections
FROM Cohort AS C
INNER JOIN Subject AS S
ON S.Id_Subject = C.Id_Subject
ORDER BY Porcentaje

as-is

ELSE 'Not elected' AS Elections

to-be

ELSE 'Not elected' END AS Elections

Answer 2

SQL 服务器案例语句的语法不正确：

SELECT column1,
             column2,
               CASE WHEN CONDITION THEN 'Value1'
               ELSE 'Value2' END AS columnX
  FROM table

您只需在语法中添加 END 即可正常工作

Answer 3

标准的大小写语法是

CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    WHEN conditionN THEN resultN
    ELSE result
END;

您可以这样写来修复您的查询

查询会更容易理解
不同的缩进更易于修改和阅读

SELECT TOP 5
  (ROUND(Registered_Students / Total_Student * 100, 2)) AS Porcentaje
, C.Total_Student
, C.Registered_Students
, S.Subject_Name
, DATEPART(YEAR, C.Date) AS Año,
    (CASE
        WHEN Porcentaje >= 75 THEN 'Elected'
        WHEN Porcentaje >= 50 THEN 'Elected 1'
        ELSE 'Not elected' END) AS Elections
FROM Cohort AS C
INNER JOIN Subject AS S
ON S.Id_Subject = C.Id_Subject
ORDER BY Porcentaje

Answer 4

列别名不能在创建时在同一个 SELECT 子句中引用。有一个 derived table（即 FROM 子句中的子查询），您可以在其中创建 Porcentaje 列。

SELECT TOP 5 dt.*,
       CASE WHEN Porcentaje >= 75 THEN 'Elected'
            WHEN Porcentaje >= 50 THEN 'Elected 1'
            ELSE 'Not elected'
       END AS Elections
FROM
(
    select
        (ROUND(Registered_Students/Total_Student * 100,2)) AS Porcentaje,
        C.Total_Student, C.Registered_Students, S.Subject_Name, DATEPART(Year, C.Date) AS Año
    FROM Cohort AS C
    INNER JOIN Subject AS S
    ON S.Id_Subject = C.Id_Subject
) dt
ORDER BY Porcentaje

带别名的案例功能

Case function with an alias

sql

case