在SQL Server中将CASE与JOIN语句一起使用

Tannya 发表于 Dev

坦雅

我需要从几个表中选择数据。第一个表包含两列Paid From和Payer Code。根据Paid From，我必须返回Student Name（从学生表）或Employee Name（从雇员表）或Account Name（从帐户表）返回。到目前为止，我在SELECT查询中使用了case表达式。我想知道是否有可能这样做LEFT JOIN。

SELECT  RV.PayerCode ,
        ( SELECT    CASE WHEN PaidFrom = 1
                         THEN ( SELECT  FullName
                                FROM    Students
                                WHERE   StudentID = RV.PayerCode
                              )
                         WHEN paidFrom = 2
                         THEN ( SELECT  AccountName
                                FROM    Accounts
                                WHERE   AccountNumber = RV.PayerCode
                              )
                         WHEN paidfrom = 3 THEN ''
                         WHEN paidFrom = 4
                         THEN ( SELECT  EmployeeName
                                FROM    Employee
                                WHERE   EmployeeID = RV.PayerCode
                              )
                    END
        ) AS PayerName 

FROM    dbo.Finance RV

普雷迪普

试试这个

SELECT RV.PayerCode,
       CASE
         WHEN RV.paidfrom = 3 THEN ''
         ELSE COALESCE(s.FullName, a.AccountName, e.EmployeeName)
       END PayerName,
FROM   dbo.Finance RV
       LEFT OUTER JOIN dbo.Students s
                    ON s.StudentID = RV.PayerCode
                       AND RV.PaidFrom = 1
       LEFT OUTER JOIN dbo.Accounts a
                    ON a.AccountNumber = RV.PayerCode
                       AND RV.PaidFrom = 2
       LEFT OUTER JOIN dbo.Employee e
                    ON e.EmployeeID = RV.PayerCode
                       AND RV.PaidFrom = 4

注意：请考虑更改数据库结构

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