如何在 SQL 的新列中使用案例信息？

Question

我正在通过在线教程系列学习 SQL，在本视频中我们学习了如何使用 case 语句。

我知道怎么用了，但后来我想“我做的专栏的新数据可以用吗？”我试过尝试并在另一个 CASE 语句中添加以尝试使用 UpdatedSalary 列，但它不起作用。我试着用谷歌搜索了一堆，但我真的不知道如何表达这个问题。

SELECT 
    FirstName, LastName, JobTitle, Salary,
    CASE 
        WHEN JobTitle = 'Salesman' THEN Salary + (Salary * .10)
        WHEN JobTitle = 'Accountant' THEN Salary + (Salary * .05)
        WHEN Jobtitle = 'HR' THEN Salary + (Salary * .00001)
        ELSE Salary + (Salary * .03)
    END AS UpdatedSalary
    CASE 
        WHEN UpdatedSalary > 0 THEN UpdatedSalary - Salary 
        ELSE 
    END AS NetIncrease
FROM 
    SQLTutorial.dbo.EmployeeDemographics
JOIN 
    SQLTutorial.dbo.EmployeeSalary ON EmployeeDemographics.EmployeeID = EmployeeSalary.EmployeeID

Answer 1

你不能像这样使用列别名，如果你想使用它你需要在两个列中放置相同的条件或者需要使用外部查询。

SELECT FirstName, LastName, JobTitle, Salary,
CASE 
    WHEN JobTitle = 'Salesman'
    THEN Salary + (Salary * .10)
    WHEN JobTitle = 'Accountant'
    THEN Salary + (Salary * .05)
    WHEN Jobtitle = 'HR' 
    THEN Salary + (Salary * .00001)
    ELSE Salary + (Salary * .03)
END
AS UpdatedSalary,

CASE 
    WHEN (CASE 
    WHEN JobTitle = 'Salesman'
    THEN Salary + (Salary * .10)
    WHEN JobTitle = 'Accountant'
    THEN Salary + (Salary * .05)
    WHEN Jobtitle = 'HR' 
    THEN Salary + (Salary * .00001)
    ELSE Salary + (Salary * .03)
END)> 0
    THEN (CASE 
    WHEN JobTitle = 'Salesman'
    THEN Salary + (Salary * .10)
    WHEN JobTitle = 'Accountant'
    THEN Salary + (Salary * .05)
    WHEN Jobtitle = 'HR' 
    THEN Salary + (Salary * .00001)
    ELSE Salary + (Salary * .03)
END)- Salary 
    ELSE
END
AS NetIncrease

FROM SQLTutorial.dbo.EmployeeDemographics
JOIN SQLTutorial.dbo.EmployeeSalary
    ON EmployeeDemographics.EmployeeID = EmployeeSalary.EmployeeID

或者

SELECT FirstName, LastName, JobTitle, Salary,UpdatedSalary,
CASE 
    WHEN UpdatedSalary > 0
    THEN UpdatedSalary - Salary 
    ELSE
END
AS NetIncrease

from (
SELECT FirstName, LastName, JobTitle, Salary,
CASE 
    WHEN JobTitle = 'Salesman'
    THEN Salary + (Salary * .10)
    WHEN JobTitle = 'Accountant'
    THEN Salary + (Salary * .05)
    WHEN Jobtitle = 'HR' 
    THEN Salary + (Salary * .00001)
    ELSE Salary + (Salary * .03)
END
AS UpdatedSalary


FROM SQLTutorial.dbo.EmployeeDemographics
JOIN SQLTutorial.dbo.EmployeeSalary
    ON EmployeeDemographics.EmployeeID = EmployeeSalary.EmployeeID)t

如何在 SQL 的新列中使用案例信息？

How can I use case information in a new column in SQL?

sql

case-statement