SQL触发器错误报告

Question

所以我得到了编写一个触发器的任务，该触发器应该在两列之间交换数据 - LAST_NAME 和 EMAIL 在更新了 SALARY 列的记录中。这就是我想出的

CREATE OR REPLACE TRIGGER SWAP
  FOR UPDATE OF SALARY ON MY_EMP
  COMPOUND TRIGGER
  AFTER EACH ROW IS
    BEGIN
      UPDATE MY_EMP SET LAST_NAME = EMAIL, EMAIL = LAST_NAME WHERE :OLD.SALARY <> :NEW.SALARY;
    END AFTER EACH ROW;
END SWAP;

当我尝试执行此操作时：

UPDATE MY_EMP
SET SALARY = SALARY + 100
WHERE EMPLOYEE_ID = 198;

我收到错误报告：

UPDATE MY_EMP
SET SALARY = SALARY + 100
WHERE EMPLOYEE_ID = 198
Error report -
SQL Error: ORA-04091: table PWR_14_15_L_013209985.MY_EMP is mutating, trigger/function may not see it
ORA-06512: at "PWR_14_15_L_013209985.SWAP", line 4
ORA-04088: error during execution of trigger 'PWR_14_15_L_013209985.SWAP'
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.

我在这里做错了什么？有什么解决办法吗？

Answer 1

将其设为更新前，而不是修改基础表，而是修改表的 :new 值。

这将允许您在 DML 提交之前更新这些内容。