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如何设置 Repeat Interval 参数，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面丸趣 TV 小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
设置 Repeat Interval
Job 和 Schedule 中 REPEAT_INTERVAL 参数都是用来控制执行的频率或周期，虽然说周期是一个时间性概念，不过 REPEAT_INTERVAL 指定的时候并不是一个时间值，而是由一组关键字描述的时间。
除了前面介绍 Job 和 Schedule 的 REPEAT_INTERVAL 参数时，提到该参数拥有 FREQ 以及 INTERVAL 两个关键字，其实除此之外，还有如 BYMONTH、BYWEEKNO、BYYEARDAY、BYDATE 等等参数，可以用来进行更精确的定义，比如通过 BYMONTH 关键字指定调度运行的月份，BYDAY 指定调度在哪天运行等等。
REPEAT_INTERVAL 参数的详细语法如下：
repeat_interval = regular_schedule | combined_schedule
==============================
regular_schedule = frequency_clause
[ interval_clause] [ bymonth_clause] [ byweekno_clause]
[ byyearday_clause] [ bydate_clause] [ bymonthday_clause]
[ byday_clause] [ byhour_clause] [ byminute_clause]
[ bysecond_clause] [ bysetpos_clause] [ include_clause]
[ exclude_clause] [ intersect_clause][ periods_clause]
[ byperiod_clause]
==============================
combined_schedule = schedule_list [ include_clause]
[ exclude_clause] [ intersect_clause]
frequency_clause = FREQ = ( predefined_frequency | user_defined_frequency )
predefined_frequency = YEARLY | MONTHLY | WEEKLY | DAILY |
HOURLY | MINUTELY | SECONDLY
user_defined_frequency = named_schedule
==============================
interval_clause = INTERVAL = intervalnum
intervalnum = 1 through 99
bymonth_clause = BYMONTH = monthlist
monthlist = monthday ( , monthday)*
month = numeric_month | char_month
numeric_month = 1 | 2 | 3 … 12
char_month = JAN | FEB | MAR | APR | MAY | JUN |
JUL | AUG | SEP | OCT | NOV | DEC
byweekno_clause = BYWEEKNO = weeknumber_list
weeknumber_list = weeknumber ( , weeknumber)*
weeknumber = [minus] weekno
weekno = 1 through 53
byyearday_clause = BYYEARDAY = yearday_list
yearday_list = yearday ( , yearday)*
yearday = [minus] yeardaynum
yeardaynum = 1 through 366
bydate_clause = BYDATE = date_list
date_list = date ( , date)*
date = [YYYY]MMDD [ offset | span ]
bymonthday_clause = BYMONTHDAY = monthday_list
monthday_list = monthday ( , monthday)*
monthday = [minus] monthdaynum
monthdaynum = 1 through 31
byday_clause = BYDAY = byday_list
byday_list = byday ( , byday)*
byday = [weekdaynum] day
weekdaynum = [minus] daynum
daynum = 1 through 53 /* if frequency is yearly */
daynum = 1 through 5 /* if frequency is monthly */
day = MON | TUE | WED | THU | FRI | SAT | SUN
byhour_clause = BYHOUR = hour_list
hour_list = hour ( , hour)*
hour = 0 through 23
byminute_clause = BYMINUTE = minute_list
minute_list = minute ( , minute)*
minute = 0 through 59
bysecond_clause = BYSECOND = second_list
second_list = second ( , second)*
second = 0 through 59
bysetpos_clause = BYSETPOS = setpos_list
setpos_list = setpos (, setpos)*
setpos = [minus] setpos_num
setpos_num = 1 through 9999
==============================
include_clause = INCLUDE = schedule_list
exclude_clause = EXCLUDE = schedule_list
intersect_clause = INTERSECT = schedule_list
schedule_list = schedule_clause (, schedule_clause)*
schedule_clause = named_schedule [ offset ]
named_schedule = [schema .] schedule
periods_clause = PERIODS = periodnum
byperiod_clause = BYPERIOD = period_list
period_list = periodnum (, periodnum)*
periodnum = 1 through 100
==============================
offset = (+ | –) [OFFSET:] duration_val
span = (+ | – | ^) SPAN: duration_val
duration_val = dur-weeks | dur_days
dur_weeks = numofweeks W
dur_days = numofdays D
numofweeks = 1 through 53
numofdays = 1 through 376
minus = –
这个语法形式看起来复杂无比，其实实用起来很简单，之所以看起来复杂，是因为其功能太过灵活 (之前的三思系列笔记中，已经阐述过灵活与复杂的关系)，这里不准备逐条解释每一个语法细节，下面将着重通过一些常用设置，希望能够更有助于广大同仁的理解。
例如：设置任务仅在周 5 的时候运行：
REPEAT_INTERVAL = FREQ=DAILY; BYDAY=FRI
REPEAT_INTERVAL = FREQ=WEEKLY; BYDAY=FRI
REPEAT_INTERVAL = FREQ=YEARLY; BYDAY=FRI
上述三条语句虽然指定的关键字小有差异，不过功能相同。
设置任务隔一周运行一次，并且仅在周 5 运行：
REPEAT_INTERVAL = FREQ=WEEKLY; INTERVAL=2; BYDAY=FRI
设置任务在当月最后一天运行：
REPEAT_INTERVAL = FREQ=MONTHLY; BYMONTHDAY=-1
设置任务在 3 月 10 日运行：
REPEAT_INTERVAL = FREQ=YEARLY; BYMONTH=MAR; BYMONTHDAY=10
REPEAT_INTERVAL = FREQ=YEARLY; BYDATE=0310
上述两条语句功能相同。
设置任务每 10 隔天运行：
REPEAT_INTERVAL = FREQ=DAILY; INTERVAL=10
设置任务在每天的下午 4、5、6 点时运行：
REPEAT_INTERVAL = FREQ=DAILY; BYHOUR=16,17,18
设置任务在每月 29 日运行：
REPEAT_INTERVAL = FREQ=MONTHLY; BYMONTHDAY=29
设置任务在每年的最后一个周 5 运行：
REPEAT_INTERVAL = FREQ=YEARLY; BYDAY=-1FRI
设置任务每隔 50 个小时运行：
REPEAT_INTERVAL = FREQ=HOURLY; INTERVAL=50
另外，你是否在怀念常规 job 中设置 interval 的简便，虽然功能较弱，但是设置操作非常简单，无须懊恼，其实 SCHEDULER 中的 REPEAT_INTERVAL 也完全可以按照那种方式设置，前面都说了，REPEAT_INTERVAL 实际上是指定周期，直接指定一个时间值，当然也是周期喽。
比如说，设置任务每天执行一次，也可以设置 REPEAT_INTERVAL 参数值如下：
REPEAT_INTERVAL = trunc(sysdate)+1
又比如设置任务每周执行一次：
REPEAT_INTERVAL = trunc(sysdate)+7
不过需要注意，这种方式仅用于创建 SCHEDULER 中 jobs 时使用，不能用于 schedule。
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