數據庫值顯示NULL

Question

我有兩個數據庫。 表1（學生）有字段StudentID，EmployeeClass，StudentName。這裏，EmployeeClass是varchar（5）。 表2（員工）具有字段EmployeeID，EmployeeName，Description和EmployeeClass。 Employee類是nvarchar（5）。

當我寫選擇查詢爲：

  SELECT S.StudentID, 
       S.EmployeeClass, 
       S.StudentName 
      FROM Student AS S 
LEFT OUTER JOIN Employee AS E 
       ON CAST(S.EmployeeClass AS VARCHAR(5)) = E.EmployeeID 
      WHERE E.Description = 'ABC' 

所有值從員工表中顯示爲空？如何修復它

Answer 1

我認爲你的script.column中的連接條件是錯誤的'EmployeeClass'在腳本中引用'EmployeeID'。

SELECT S.StudentID, 
       S.EmployeeClass, 
       S.StudentName 
FROM Student AS S 
    LEFT JOIN Employee AS E 
      ON cast(S.EmployeeClass as varchar(5))= E.EmployeeClass 
      AND E.Description = 'ABC'