我们都知道Job 和Schedule中REPEAT_INTERVAL参数是用来控制执行的频率和周期，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 参数的详细语法非常复杂，为了让大家更好的理解，我这里先举一些例子，大家先有个感官上的认识

1、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。

2、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';

3、设置任务在当月最后一天运行

REPEAT_INTERVAL => 'FREQ=MONTHLY; BYMONTHDAY=-1';

4、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。

5、设置任务每隔10天运行

REPEAT_INTERVAL => 'FREQ=DAILY; INTERVAL=10';

6、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';

7、设置任务在每月29日运行

REPEAT_INTERVAL => 'FREQ=MONTHLY; BYMONTHDAY=29';

8、设置任务在每年的最后一个周5运行

REPEAT_INTERVAL => 'FREQ=YEARLY; BYDAY=-1FRI';

这里的配置可能稍微复杂点，大家先记着，后面会详细解释。

9、设置任务每隔50个小时运行

REPEAT_INTERVAL => 'FREQ=HOURLY; INTERVAL=50';

10、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'

11、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。

下面对repeat_interval的详细参数进行解释。

------------------------------------------------------------------

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 = "-"

这个语法相信大家看起来是不是复杂无比，其实实用起来也没那么复杂，之所以看起来复杂，是因为其功能太过灵活，通过开篇一些常用设置的举例，大家应该有个认识就够了。

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