不能正确引发异常的 PLSQL 函数

Question

我正在编写一个函数，用于在输入 ID 时返回学生的姓名。如果输入了数据库中不存在的 ID，我希望引发异常。相反，当我输入错误的学生 ID 时，如果我抛出了基本异常，它要么不返回任何内容，要么返回此错误消息并声明异常：

6503. 00000 -  "PL/SQL: Function returned without value"
*Cause:    A call to PL/SQL function completed, but no RETURN statement was
       executed.
*Action:   Rewrite PL/SQL function, making sure that it always returns
       a value of a proper type.

这是我的功能：

CREATE OR REPLACE Function STUDENT( S_NUM IN NUMBER)
RETURN varchar2 IS
STUDENT_NAME varchar2(50);
NOTEXISTS   EXCEPTION;
   cursor S_CUR is
   SELECT S_NAME
      FROM ROSTER
      WHERE S_NUM = S_ID;
BEGIN
   open S_CUR;
   fetch S_CUR into STUDENT_NAME;

   if S_CUR%notfound then
      RAISE NOTEXISTS;
   end if;
   close S_CUR;
RETURN STUDENT_NAME;

EXCEPTION
WHEN NOTEXISTS THEN -- handle the error
      dbms_output.put_line('NO STUDENT FOUND.');
END;

有什么想法吗？

Answer 1

发生异常时，您不会返回实际的错误消息。您的函数应该返回 varchar。但是，您只是打印错误而不返回实际的错误消息。

EXCEPTION
WHEN NOTEXISTS THEN -- handle the error
      dbms_output.put_line('NO STUDENT FOUND.');
      return 'No Student Found'
END;

Answer 2

首先，不要定义您自己的仅在您的函数上下文中有效的异常，而是使用为这种情况定义的标准异常 - NO_DATA_FOUND 异常：

CREATE OR REPLACE Function STUDENT(S_NUM IN ROSTER.S_ID%TYPE)
    -- Exceptions: raises NO_DATA_FOUND if the student ID passed in
    --             parameter S_NUM is not found in the STUDENT table.
    RETURN ROSTER.S_NAME%TYPE
IS
  STUDENT_NAME ROSTER.S_NAME%TYPE;
  bData_found  BOOLEAN;

 CURSOR S_CUR IS
   SELECT S_NAME
      FROM ROSTER
      WHERE S_NUM = S_ID;
BEGIN
  OPEN S_CUR;

  FETCH S_CUR INTO STUDENT_NAME;

  bData_found := S_CUR%NOTFOUND;

  CLOSE S_CUR;

  IF bData_found THEN
    RETURN STUDENT_NAME;    
  ELSE
    RAISE NO_DATA_FOUND;
  END IF;
END STUDENT;

其次，不要在函数中处理异常。异常的目的是允许代码将异常情况传达给其他代码。让调用者处理异常，如：

DECLARE
  nStudent_id      ROSTER.S_ID%TYPE := 12345;
  strStudent_name  ROSTER.S_NAME%TYPE;
BEGIN
  strStudent_name := STUDENT(nStudent_id);
  DBMS_OUTPUT.PUT_LINE('S_ID=' || nStudent_id || '  NAME=' || strStudent_name);
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    DBMS_OUTPUT.PUT_LINE('NO STUDENT FOUND.');
END;

祝你好运。