Question

    select Firstname,LastName,age, case
    when age < 40 and age >= 25 then 'Young' 
    when age < 60 and age >= 40 then 'No More Young'
    when age >= 60 then 'Retired'
    else 'Dont Care'
    END as flag
    from (select FirstName,LastName,DATEDIFF(year,2018-08-26,BirthDate) as age from ContosoRetailDW.dbo.DimCustomer)

我在执行代码时遇到问题， '）'附近的语法不正确。

我现在正在学习SQL，因此将不胜感激。

Answer 1

问题不是case表达式。您缺少子查询的表别名。此外，日期常数必须用单引号引起来：

select Firstname, LastName, age,
       (case when age < 40 and age >= 25 then 'Young' 
             when age < 60 and age >= 40 then 'No More Young'
             when age >= 60 then 'Retired'
             else 'Dont Care'
        end) as flag
from (select FirstName, LastName, DATEDIFF(year, '2018-08-26', BirthDate) as age
      from ContosoRetailDW.dbo.DimCustomer
     ) c;

您可以通过确认条件按顺序求值来简化case逻辑：

select Firstname, LastName, age,
       (case when age >= 25  and age < 40 then 'Young' 
             when age < 60 then 'No More Young'
             when age >= 60 then 'Retired'
             else 'Dont Care'
        end) as flag
from (select FirstName, LastName, DATEDIFF(year, '2018-08-26', BirthDate) as age
      from ContosoRetailDW.dbo.DimCustomer
     ) c;

这只是一个简单的映射，只映射了三个范围。

Answer 2

您应该只在查询末尾添加“作为客户”。原因是，每个子查询都必须有一个别名。提供其他所有方法都是正确的（我不确定此DATEDIFF版本）应该可以正常工作。

将SQL子查询与case语句一起使用时的问题

2 个答案: