Oracle sql中的触发器：突变触发器问题

我想在尝试表中插入行时，将行插入另一个名为exercise_scores的表中。一次练习有多次尝试，根据评分方法（可以是最新分数、所有尝试的平均值或所有尝试的最大分数），我必须在练习分数表中插入分数。
因此，在将分数插入练习分数时，我还必须检查练习的评分方法，根据该方法从尝试表中获取分数，然后最后插入练习分数表

为此，我创建了一个SQL触发器，如下所示

CREATE OR REPLACE TRIGGER scores_trigger AFTER
 INSERT
  ON attempts FOR EACH row DECLARE P1 VARCHAR2(50);
 SCORES FLOAT;
 v_exists VARCHAR2(1) := 'F';
 BEGIN
  BEGIN
   SELECT
    'T'
     INTO
     v_exists
   FROM
     excercise_scores
   WHERE
    user_id        = :NEW.USER_ID
    AND EXCERCISE_ID = :NEW.EXCERCISE_ID
    AND COURSE_ID    = :NEW.COURSE_ID;
   EXCEPTION
    WHEN no_data_found THEN
    NULL;
  END;
 SELECT
  SELECTION_METHOD
 INTO
  P1
 FROM
  EXCERCISES
 WHERE
  EXCERCISE_ID = :NEW.EXCERCISE_ID
 AND COURSE_ID  = :NEW.COURSE_ID;
 IF (P1         = 'Latest') THEN
   SCORES      := :NEW.TOTAL_POINTS;
 ELSE
   IF (P1 = 'best') THEN
     SELECT
       MAX(TOTAL_POINTS)
     INTO
       SCORES
     FROM
      ATTEMPTS
     WHERE
      EXCERCISE_ID = :NEW.EXCERCISE_ID
     AND COURSE_ID  = :NEW.COURSE_ID
     AND USER_ID    = :NEW.USER_ID;         
   ELSE
     SELECT
       AVG(TOTAL_POINTS)
     INTO
       SCORES
     FROM
       ATTEMPTS
     WHERE
       EXCERCISE_ID = :NEW.EXCERCISE_ID
     AND COURSE_ID  = :NEW.COURSE_ID
     AND USER_ID    = :NEW.USER_ID;
   END IF;
 END IF;
 IF v_exists = 'T' THEN
   UPDATE
     EXCERCISE_SCORES
   SET
     TOTAL_POINTS = SCORES
   WHERE
     user_id        = :NEW.USER_ID
   AND EXCERCISE_ID = :NEW.EXCERCISE_ID
   AND COURSE_ID    = :NEW.COURSE_ID;
 ELSE
   INSERT
   INTO
     EXCERCISE_SCORES VALUES
     (
       :NEW.EXCERCISE_ID,
       :NEW.COURSE_ID,
       :NEW.COURSE_ID,
       SCORES
      ) ;
 END IF;
END;

但当我尝试执行此触发器时，它会给我以下错误：

Error starting at line 47 in command:
insert into attempts values(21,0,'vshesha',3,'CSC540',TO_DATE('20141014', 'YYYYMMDD'),12,6)
Error report:
SQL Error: ORA-04091: table VSHESHA.ATTEMPTS is mutating, trigger/function may not see it
ORA-06512: at "VSHESHA.SCORES_TRIGGER", line 18
ORA-04088: error during execution of trigger 'VSHESHA.SCORES_TRIGGER'
04091. 00000 -  "table %s.%s is mutating, trigger/function may not see it"
*Cause:    A trigger (or a user defined plsql function that is referenced in
       this statement) attempted to look at (or modify) a table that was
       in the middle of being modified by the statement which fired it.
*Action:   Rewrite the trigger (or function) so it does not read that table.

我无法理解为什么它会给出这个错误，因为我在插入后运行触发器。通常情况下，在插入触发器之后不应出现变异表问题

---

谁能帮我一下吗。很长一段时间以来，我一直对这个问题感到厌烦。

错误消息是非常自我解释的，导致它的SQL语句是：

     SELECT
       AVG(TOTAL_POINTS)
     INTO
       SCORES
     FROM
       ATTEMPTS
     WHERE
       EXCERCISE_ID = :NEW.EXCERCISE_ID
     AND COURSE_ID  = :NEW.COURSE_ID
     AND USER_ID    = :NEW.USER_ID;

您正在从

尝试中进行选择，这就是当前正在更改的表。没有简单的解决方案—最明智的方法是使用将业务逻辑移出触发器并放入应用程序代码中（请参阅）

顺便说一句：您的声明“通常情况下，在插入触发器之后不应该出现表问题。”是完全错误的。请参阅以获得更详细的解释（简而言之：多行插入总是会遇到变异表错误，几乎在所有情况下，单行插入都会遇到错误）。
在Oralce中，您可以使用。在你的情况下，它将类似于这个。我没有把你所有的操作都复制到这个例子中，但是你应该得到原理

然而，正如其他答复已经提到的那样。首选的方法应该是将所有这些逻辑移到PL/SQL过程中

CREATE OR REPLACE TRIGGER scores_trigger
    FOR INSERT ON attempts
    COMPOUND TRIGGER

    TYPE RowTableType IS TABLE OF ROWID;
    RowTable RowTableType;
    aRow attempts%ROWTYPE;

    SCORES FLOAT;
    v_exists VARCHAR2(1) := 'F';

    BEFORE STATEMENT IS
    BEGIN
        RowTable := RowTableType();
    END BEFORE STATEMENT;

    AFTER EACH ROW IS
    BEGIN
        RowTable.EXTEND;
        RowTable(RowTable.LAST) := :NEW.ROWID;
    END AFTER EACH ROW;

    AFTER STATEMENT IS
    BEGIN

        FOR i IN RowTable.FIRST..RowTable.LAST LOOP
            SELECT * 
            INTO aRow
            FROM attempts
            WHERE ROWID = RowTable(i);

            SELECT SELECTION_METHOD
            INTO P1
            FROM EXCERCISES
            WHERE EXCERCISE_ID = aRow.EXCERCISE_ID
                AND COURSE_ID  = aRow.COURSE_ID;

            IF P1 = 'Latest' THEN
                SCORES := :NEW.TOTAL_POINTS;
            ELSE
                IF (P1 = 'best') THEN
                    SELECT MAX(TOTAL_POINTS)
                    INTO SCORES
                    FROM ATTEMPTS
                    WHERE EXCERCISE_ID = aRow.EXCERCISE_ID
                        AND COURSE_ID  = aRow.COURSE_ID
                        AND USER_ID    = aRow.USER_ID;         
                ELSE
                    SELECT AVG(TOTAL_POINTS)
                    INTO SCORES
                    FROM ATTEMPTS
                    WHERE EXCERCISE_ID = aRow.EXCERCISE_ID
                        AND COURSE_ID  = aRow.COURSE_ID
                        AND USER_ID    = aRow.USER_ID;
                END IF;
            END IF;

        END LOOP;

    END AFTER STATEMENT;
END scores_trigger;

PL/SQL过程的一个示例如下：

CREATE OR REPLACE PROCEDURE insert_score(V_EXCERCISE IN SCORES.EXCERCISE_ID%TYPE, V_COURSE IN SCORES.COURSE_ID%TYPE, V_USER IN USER_ID%TYPE) IS

BEGIN
    INSERT INTO insert_score (EXCERCISE_ID, COURSE_ID, USER_ID) VALUES (V_EXCERCISE, V_COURSE, V_USER);

    BEGIN
    SELECT 'T'
    INTO v_exists
    FROM excercise_scores
    WHERE user_id        = :NEW.USER_ID
        AND EXCERCISE_ID = :NEW.EXCERCISE_ID
        AND COURSE_ID    = :NEW.COURSE_ID;
    EXCEPTION
        WHEN NO_DATA_FOUND THEN
            RETURN;
    END;

    ... other stuff

END insert_score;

对于插入，您必须调用此过程，而不是直接执行插入。
SQL错误：ORA-04091
？请调整您的标签我是新的触发器，我不知道如何才能做到这一点。我应该将逻辑移到哪里以及如何移动？我假设您有某种使用数据库的应用程序。据推测，此应用程序是用不同于SQL的编程语言编写的。在插入操作后使用该编程语言更新数据，或者将逻辑放入PL/SQL存储过程中，该存储过程首先执行插入，然后执行辅助插入/更新。非常感谢！我又在类似的行上写了触发器。@Kristy，不要说“谢谢”，接受答案并投票表决。投票表决需要15的声望，而我现在还没有：(