PLSQL：触发器的语法问题

Question

我已经创建了很多类似的触发器，因此我习惯于发现常见的 sntax 错误 - 例如，忘记 END IF 或 THEN。我无法编译这个

CREATE OR REPLACE TRIGGER SOLD
BEFORE UPDATE OF STATUS ON STORE_COPY
FOR EACH ROW
DECLARE 
RENT_OR_SALE NVARCHAR2(6);
UPDATED_DVD_ID NUMBER(10);
BEGIN
UPDATED_DVD_ID := SELECT DVD_ID FROM STORE_COPY WHERE :NEW.STATUS != :OLD.STATUS;
RENT_OR_SALE := SELECT (SELECT RENT_OR_SALE FROM DVD JOIN STORE_COPY ON STORE_COPY.DVD_ID =     DVD.DVD_ID WHERE :NEW.STATUS != :OLD.STATUS) INTO RENT_OR_SALE FROM DUAL;
IF :NEW.STATUS != :OLD.STATUS
THEN
IF :OLD.STATUS = 'Y'
THEN
IF :NEW.STATUS = 'N'
THEN
IF RENT_OR_SALE = 'S'
THEN
INSERT INTO SOLD VALUES(NULL, CURRENT_TIMESTAMP, (SELECT PRICE FROM DVD JOIN STORE_COPY ON       STORE_COPY.DVD_ID = DVD.DVD_ID WHERE :NEW.DVD_IS = UPDATED_DVD_ID), :NEW.DVD_ID);
END IF;
END IF;
END IF;
END IF;
END;
/

终端通过“显示错误”命令向我提供以下信息：

Warning: Trigger created with compilation errors.

SQL> show errors;
LINE/COL ERROR
-------- -----------------------------------------------------------------
5/23     PLS-00103: Encountered the symbol "SELECT" when expecting one of
 the following:
 ( - + case mod new not null <an identifier>
 <a double-quoted delimited-identifier> <a bind variable>
 continue avg count current exists max min prior sql stddev
 sum variance execute forall merge time timestamp interval
 date <a string literal with character set specification>
 <a number> <a single-quoted SQL string> pipe
 <an alternatively-quoted string literal with character set
 specification>
 <an alternat

LINE/COL ERROR
-------- -----------------------------------------------------------------

6/5  PLS-00103: Encountered the symbol "RENT_OR_SALE" 

Answer 1

您不能在 IF 检查条件中使用“select”子句。使用 select INTO 变量，然后在 IF() 中检查该变量。参见示例：if (select count(column) from table) > 0 then

Answer 2

您需要使用SELECT...INTO...。 PL/SQL 中没有variable := SELECT...。一个起点是：

CREATE OR REPLACE TRIGGER SOLD
  BEFORE UPDATE OF STATUS ON STORE_COPY
  FOR EACH ROW
DECLARE 
  strRENT_OR_SALE NVARCHAR2(6);
  nUPDATED_DVD_ID NUMBER(10);
BEGIN
  SELECT DVD_ID
    INTO nUPDATED_DVD_ID
    FROM STORE_COPY
    WHERE :NEW.STATUS != :OLD.STATUS;

  SELECT RENT_OR_SALE
    INTO strRENT_OR_SALE
    FROM DVD
    JOIN STORE_COPY
      ON STORE_COPY.DVD_ID = DVD_ID
    WHERE :NEW.STATUS != :OLD.STATUS;

  IF :NEW.STATUS != :OLD.STATUS THEN
    IF :OLD.STATUS = 'Y' THEN
      IF :NEW.STATUS = 'N' THEN
        IF RENT_OR_SALE = 'S' THEN
          INSERT INTO SOLD VALUES
            (NULL,
             CURRENT_TIMESTAMP,
             (SELECT PRICE
                FROM DVD
                JOIN STORE_COPY
                  ON STORE_COPY.DVD_ID = DVD.DVD_ID
                WHERE :NEW.DVD_IS = UPDATED_DVD_ID),
             :NEW.DVD_ID);
        END IF;
      END IF;
    END IF;
  END IF;
END;

但即便如此，您仍然会遇到错误。我怀疑那些 SELECT 是单例的（也就是说，它们可能返回不止一行），所以它们会在运行时进行调整。即使你完成了那个，你仍然会得到一个 ORA-04091 错误（表正在变异；触发器看不到它），因为你在这个触发器中有 SELECT 语句读取触发器所在的表开。

您试图在那些SELECT FROM STORE_COPY... 语句中读取的值是否应该与刚刚修改的相同？如果是这样，它们可用作 :OLD 和 :NEW 值，因此以下可能有效：

CREATE OR REPLACE TRIGGER SOLD
  BEFORE UPDATE OF STATUS ON STORE_COPY
  FOR EACH ROW
DECLARE 
  strRENT_OR_SALE NVARCHAR2(6);
  nPrice          NUMBER;
BEGIN
  SELECT RENT_OR_SALE,
         PRICE
    INTO strRENT_OR_SALE,
         nPrice
    FROM DVD d
    WHERE d.DVD_ID = :NEW.DVD_ID

  IF :OLD.STATUS = 'Y' AND
     :NEW.STATUS = 'N' AND
     strRENT_OR_SALE = 'S'
  THEN
    INSERT INTO SOLD VALUES
      (NULL,
       CURRENT_TIMESTAMP,
       nPrice);
  END IF;
END TRIGGER_SOLD;

我可能猜错了某些字段的位置（例如，我猜到 PRICE 在 DVD 上。如果它实际上在 STORE_COPY 上，那么您可能可以改用 :NEW.PRICE）。

分享和享受。

Answer 3

所以删除“;”来自：

:NEW.STATUS != :OLD.STATUS;),