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  • 开发PL/SQL子程序——触发器——使用触发器注意事项



    当编写dml触发器时,触发器代码不能从触发器所对应的表中读取数据。例如,如果要基于emp表建立触发器,那么该出发起的执行代码不能包含对emp表的查询操作。尽管机那里触发器时不会出现任何错误,但在执行相应触发操作时会显示错误的信息。假定要确保雇员的新工资不能超过当前的最高工资,并使用触发器实现;

    create or replace trigger tr_emp_sal
    before update of sal on emp for each row
    declare maxsal number(6,2);
    begin
    select max(sal)into maxsal from emp ;
    if :new.sal>maxsal then
    raise_application_error(-20001,'超出工资上限');
    end if;
    end;
    /

    update emp set sal =60000 where empno=7788;


    在行 1 上开始执行命令时出错:
    update emp set sal =60000 where empno=7788
    错误报告:
    SQL 错误: ORA-04091: 表 SCOTT.EMP 发生了变化, 触发器/函数不能读它
    ORA-06512: 在 "SCOTT.TR_EMP_SAL", line 3
    ORA-04088: 触发器 'SCOTT.TR_EMP_SAL' 执行过程中出错
    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.


    -------------------------------------------

    作者:赵杰迪

    -------------------------------------------

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  • 原文地址:https://www.cnblogs.com/zhaojiedi1992/p/oracle11g_sql_0024.html
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