在 SQL 服务器中使用 CASE 和 JOIN 语句

Question

我需要 select 来自几个 table 的数据。第一个 table 包含两列 Paid From 和 Payer Code。根据 Paid From，我必须 return Student Name（来自学生 Table）或 Employee Name（来自员工 Table）或 Account Name（来自帐户 Table）。截至目前，我在 SELECT 查询中使用了 case 表达式。我想知道是否可以在 LEFT JOIN.

中这样做

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

Answer 1

尝试这样的事情

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：考虑更改数据库结构

在 SQL 服务器中使用 CASE 和 JOIN 语句

Use CASE with JOIN Statements in SQL Server

sql-server

case

left-join

sql-server-2008