https://blogs.oracle.com/oracle4engineer/oracle-functions-%e3%81%a8-events:-%e3%83%9e%e3%83%8d%e3%83%bc%e3%82%b8%e3%83%89%e3%83%bb%e3%82%b5%e3%83%bc%e3%83%93%e3%82%b9%e3%81%a7%e7%85%a9%e9%9b%91%e3%81%95%e3%82%92%e6%89%93%e7%a0%b4