我正在尝试查找数据库中是否有一位以上的主席带触发器,如果是,请引发错误,我正在使用hr,表employees,并且必须使用job_id来找到它。这是我的代码的样子。谢谢!
CREATE OR REPLACE TRIGGER check_pres
BEFORE INSERT OR DELETE OR UPDATE ON employees
FOR EACH ROW
BEGIN
IF ((employees.job_id = 'AD_PRES') > 1)
THEN RAISE_APPLICATION_ERROR(-12345, 'More than one President in database.');
END IF;
END;
您应该通过删除Statement Level Trigger
表达式使用Row Level Trigger
而不是FOR EACH ROW
CREATE OR REPLACE TRIGGER check_pres
BEFORE INSERT OR DELETE OR UPDATE ON employees
DECLARE
v_cnt int;
BEGIN
SELECT COUNT(*) INTO v_cnt FROM employees WHERE job_id = 'AD_PRES';
IF ( v_cnt > 1 ) THEN
RAISE_APPLICATION_ERROR(-20345, 'More than one President in database.');
END IF;
END;
否则,在获取计数值时会发生变异错误。顺便说一句,RAISE_APPLICATION_ERROR
的第一个参数值应介于-20999
和-20000