Question

SELECT DISTINCT AppID,
                CASE
                  WHEN Category = '< 18 years old' THEN 'yes'
                  ELSE ''
                END AS '<18years old',
                CASE
                  WHEN Category = 'SSN Exists' THEN 'yes'
                  ELSE ''
                END AS 'Applicant has SSN',
                CASE
                  WHEN Category = 'Self Employed' THEN 'yes'
                  ELSE ''
                END AS 'Self employed'
FROM   Table1
WHERE  AppID = 123

OUTPUT Desired 我正在尝试生成下面的结果，其中每个AppID只有1行所有与之相关的信息。上面的代码产生多行为每个应用程序。我试图将case语句与1 END结合在一起，但是当我在END关键字之前使用别名时出现错误。感谢

AppID         <18 Year old           Applicant has SSN           Self employed  

123     yes         yes
124                 yes         yes
125                 yes         yes

Answer 1

您需要group by而不是distinct：

SELECT AppID,
       max(CASE WHEN Category = '< 18 years old' THEN 'yes'
                ELSE ''
           END) AS '<18years old',
       max(CASE WHEN Category) = 'SSN Exists' THEN 'yes'
                ELSE ''
           END) AS 'Applicant has SSN',
       max(CASE WHEN Category = 'Self Employed' THEN 'yes'
                ELSE ''
           END) AS 'Self employed'
FROM   Table1
WHERE  AppID = 123
group by AppId

Answer 2

您可以按如下方式嵌套Case语句，最后只是别名：

CASE WHEN 
    Category = '< 18 years old' 
THEN 'yes'
ELSE
    CASE WHEN
        Category = 'SSN Exists'
    THEN 'yes'
    ELSE
        ...
        ...
    END
END AS Alias

这就是你要追求的吗？

Answer 3

您的别名不应包含在''。

中

检查数据库引擎必须使用哪种字符来封装别名。

Answer 4

如果我正确理解您的问题，您需要执行GROUP BY：

SELECT  AppID,
        MAX(CASE
          WHEN Category = '< 18 years old' THEN 'yes'
          ELSE ''
        END) AS '<18years old',
        MAX(CASE
          WHEN Category = 'SSN Exists' THEN 'yes'
          ELSE ''
        END) AS 'Applicant has SSN',
        MAX(CASE
          WHEN Category = 'Self Employed' THEN 'yes'
          ELSE ''
        END) AS 'Self employed'
FROM   Table1
WHERE  AppID = 123 
GROUP BY AppID

带有别名的SQL中的多个Case语句

4 个答案: