oracle查看当前日期是第几个星期的方法

系统当前时间是多少周，就是是今年的第几个星期
 

   
select to_char(sysdate,'ww') ,to_char(sysdate,'iw') from dual;
select to_char(sysdate,'ddd') from dual;
select trunc(sysdate,'mm') from dual;1）

ww的算法为每年1月1日为第一周开始，date+6为每一周结尾
例如:20050101为第一周的第一天，而第一周的最后一天为20050101+6=20050107　　
公式: 每周第一天 ：date + 周 * 7 - 7　　每周最后一天：date + 周 * 7 - 12）

iw的算法为星期一至星期日算一周，且每年的第一个星期一为第一周，
例如:20050101为星期六，所以用iw的算法是前年的53周，而20050103之后才是第一周的开始。　　
公式: 每周第一天 ：next_day(date) + 周 * 7 - 7每周最后一天：next_day(date) + 周 * 7 - 13）

其它：　　
a、查今天是 "本月" 的第几周　　select to_char(sysdate,'ww') - to_char(trunc(sysdate,'mm'),'ww') + 1 as "weekofmon" from dual;　　或　　select to_char(sysdate,'w') as "weekofmon" from dual;　　
b、查今天是 "今年" 的第几周　　select to_char(sysdate,'ww') from dual;　　或　　select to_char(sysdate,'iw') from dual;
统计哪年哪个星期的哪一天：

 int year=2011;
        int week=1;
        calendar calfirstdayoftheyear = new gregoriancalendar(year,
                calendar.january, 1);
            calfirstdayoftheyear.add(calendar.date, 7 * (week-1));

 
            int dayofweek = calfirstdayoftheyear.get(calendar.day_of_week);

 
            calendar calfirstdayinweek = (calendar)calfirstdayoftheyear.clone();
            calfirstdayinweek.add(calendar.date,
                calfirstdayoftheyear.getactualminimum(calendar.day_of_week) - dayofweek);
            date firstdayinweek = calfirstdayinweek.gettime();
            system.out.println(year + "年第" + week + "个礼拜的第一天是" + reportdateutil.getfromatday().format(firstdayinweek));

 
            calendar callastdayinweek = (calendar)calfirstdayoftheyear.clone();
            callastdayinweek.add(calendar.date,
                calfirstdayoftheyear.getactualmaximum(calendar.day_of_week) - dayofweek);
            date lastdayinweek = callastdayinweek.gettime();
            system.out.println(year + "年第" + week + "个礼拜的最后一天是" + reportdateutil.getfromatday().format(lastdayinweek));