Oracle定时任务 时间间隔
当定义oracle定时任务时，时间间隔的定义是，一次任务的结束时刻到另一次任务的开始时刻。
当定义Oracle定时任务时，时间间隔的定义是，一次任务的结束时刻到另一次任务的开始时刻。
例：select (TRUNC(sysdate,'mi') + 1 / (24*60)),(sysdate + 1 / (24*60)) from dual
错误：sysdate + 1 / (24*60)作为时间间隔，这样每次计算下次执行时间时，，会把当前时间加进去，也就是任务的执行时间被加进去了。
正确：TRUNC(sysdate,'mi') + 1 / (24*60)，用trunc忽略当前时间的误差（就是执行任务多出的时间）。这里首先我们要有共识，即按分钟跑的任务执行时间不能超过一分钟，按小时跑的任务执行时间不能超过一个小时，按天执行的任务执行时间不能超过一个小时。这样我们就可以用trunc去大胆的忽略，小时：TRUNC(sysdate,'hh24') + 1 / 24, 天:TRUNC(sysdate,'dd') + 1
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