触发器--------------------------------------------------------------------------------创建触发器:
CREATE [OR REPLACE] TRIGGER
BEFORE|AFTER
INSERT|DELETE|UPDATE [OF ] ON
[FOR EACH ROW]
WHEN ()
关键字"BEFORE"在操作完成前触发;"AFTER"则是在操作完成后触发;
关键字"FOR EACH ROW"指定触发器每行触...
