?? 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。??
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　　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。??
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　　REPEAT_INTERVAL 参数的详细语法如下：??
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?? repeat_interval = regular_schedule | combined_schedule??
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regular_schedule = frequency_clause??
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[";" interval_clause] [";" bymonth_clause] [";" byweekno_clause]??
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[";" byyearday_clause] [";" bydate_clause] [";" bymonthday_clause]??
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[";" byday_clause] [";" byhour_clause] [";" byminute_clause]??
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[";" bysecond_clause] [";" bysetpos_clause] [";" include_clause]??
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[";" exclude_clause] [";" intersect_clause][";" periods_clause]??
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[";" byperiod_clause]??
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combined_schedule = schedule_list [";" include_clause]??
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[";" exclude_clause] [";" intersect_clause]??
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frequency_clause = "FREQ" "=" ( predefined_frequency | user_defined_frequency )??
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predefined_frequency = "YEARLY" | "MONTHLY" | "WEEKLY" | "DAILY" |???
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?? "HOURLY" | "MINUTELY" | "SECONDLY"?
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user_defined_frequency = named_schedule??
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interval_clause = "INTERVAL" "=" intervalnum??
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?? intervalnum = 1 through 99??
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bymonth_clause = "BYMONTH" "=" monthlist??
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?? monthlist = monthday ( "," monthday)*??
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?? month = numeric_month | char_month??
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?? numeric_month = 1 | 2 | 3 ...? 12??
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?? char_month = "JAN" | "FEB" | "MAR" | "APR" | "MAY" | "JUN" |??
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?? "JUL" | "AUG" | "SEP" | "OCT" | "NOV" | "DEC"?
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byweekno_clause = "BYWEEKNO" "=" weeknumber_list??
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?? weeknumber_list = weeknumber ( "," weeknumber)*??
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?? weeknumber = [minus] weekno??
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?? weekno = 1 through 53??
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byyearday_clause = "BYYEARDAY" "=" yearday_list??
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?? yearday_list = yearday ( "," yearday)*??
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?? yearday = [minus] yeardaynum??
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?? yeardaynum = 1 through 366??
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bydate_clause = "BYDATE" "=" date_list??
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?? date_list = date ( "," date)*??
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?? date = [YYYY]MMDD [ offset | span ]??
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bymonthday_clause = "BYMONTHDAY" "=" monthday_list??
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?? monthday_list = monthday ( "," monthday)*??
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?? monthday = [minus] monthdaynum??
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?? monthdaynum = 1 through 31??
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byday_clause = "BYDAY" "=" byday_list??
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?? byday_list = byday ( "," byday)*??
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?? byday = [weekdaynum] day??
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?? weekdaynum = [minus] daynum??
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?? daynum = 1 through 53 /* if frequency is yearly */?
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?? daynum = 1 through 5? /* if frequency is monthly */?
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?? day = "MON" | "TUE" | "WED" | "THU" | "FRI" | "SAT" | "SUN"?
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byhour_clause = "BYHOUR" "=" hour_list??
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?? hour_list = hour ( "," hour)*??
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?? hour = 0 through 23??
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byminute_clause = "BYMINUTE" "=" minute_list??
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?? minute_list = minute ( "," minute)*??
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?? minute = 0 through 59??
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bysecond_clause = "BYSECOND" "=" second_list??
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?? second_list = second ( "," second)*??
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?? second = 0 through 59??
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bysetpos_clause = "BYSETPOS" "=" setpos_list??
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?? setpos_list = setpos ("," setpos)*??
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?? setpos = [minus] setpos_num??
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?? setpos_num = 1 through 9999??
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include_clause = "INCLUDE" "=" schedule_list??
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exclude_clause = "EXCLUDE" "=" schedule_list??
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intersect_clause = "INTERSECT" "=" schedule_list??
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schedule_list = schedule_clause ("," schedule_clause)*??
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schedule_clause = named_schedul