PL / SQL触发器具有来自更新的特定变量

Question

I'm trying to trigger an update after an update.

My Tables:

CREATE TABLE STUDENT (
  STUDENT_ID          INTEGER     PRIMARY KEY,
  NAME                CHAR(40)    NOT NULL,
  SURNAME             CHAR(40)    NOT NULL,
  TOKEN               CHAR(5)     NOT NULL,
  STUDYCOURSE         CHAR(20)    NOT NULL,
  NOTE                VARCHAR(255)    NULL,
  WARNING_ID          INTEGER     REFERENCES MAHNUNG (ID),
  BLOCKED             CHAR(1)     CHECK (Gesperrt IN('J', 'N'));

create table RENTAL (
  RENTAL_ID           INTEGER     PRIMARY KEY,
  RENTALDATE          DATE        DEFAULT SYSDATE,
  RENTALDURATION      INTEGER     NOT NULL,
  OVERDRAWN           CHAR(1)     CHECK (OVERDRAWN IN('Y', 'N'));

My Trigger:

CREATE OR REPLACE TRIGGER OVERDRAWN_RETURN
AFTER UPDATE OF OVERDRAWN ON RENTAL
  REFERENCING OLD AS OLD AND NEW AS NEW

BEGIN
  IF :NEW.OVERDRAWN := 'Y' THEN
  UPDATE STUDENT SET WARNING_ID = WARNING_ID+1
  WHERE STUDENT.STUDENT_ID = RENTAL.STUDENT_ID;
  END IF;
END OVERDRAWN_RETURN;
/

What I'm basically trying to do is increment the WARNING_ID when OVERDRAWN is updated to 'Y' (yes). Error report -

ORA-04079: invalid trigger specification
04079. 00000 -  "invalid trigger specification"
*Cause:    The create TRIGGER statement is invalid.
*Action:   Check the statement for correct syntax.

What did I do wrong?

Answer 1

you were using assignment operator(:=) in IF statement.

  CREATE OR REPLACE TRIGGER OVERDRAWN_RETURN
    AFTER UPDATE OF OVERDRAWN ON RENTAL
      REFERENCING OLD AS OLD AND NEW AS NEW

    BEGIN
      IF :NEW.OVERDRAWN = 'Y' THEN
      UPDATE STUDENT SET WARNING_ID = WARNING_ID+1
      WHERE STUDENT.STUDENT_ID = RENTAL.STUDENT_ID;
      END IF;
    END OVERDRAWN_RETURN;
    /

Answer 2

As well as the use of := instead of = for comparison that @Prashant pointed out, there are some other issues. The actual error you see is because of the REFERENCING line, which should not have the AND .

But you can't use new and old for statement triggers, so you need to make it a FOR EACH ROW trigger too:

CREATE OR REPLACE TRIGGER OVERDRAWN_RETURN
AFTER UPDATE OF OVERDRAWN ON RENTAL
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW

BEGIN
  IF :NEW.OVERDRAWN = 'Y' THEN
    UPDATE STUDENT SET WARNING_ID = WARNING_ID+1
    WHERE STUDENT_ID = :NEW.STUDENT_ID;
  END IF;
END OVERDRAWN_RETURN;
/

You were referring to RENTAL.STUDENT_ID , but that is out of scope for the SQL statement. So I've changed that to refer to the current row, with :NEW.STUDENT_ID . But either way, your RENTAL table doesn't have a STUDENT_ID column, but you may have just omitted that when editing the definition for posting.