方法是：获取当前日期的下一个星期一，然后再减4天
year(date_sub(next_day('2015-01-01','monday'),4))*100 + weekofyear('2015-01-01')
减4的原因：这周哪年的天数多，就属于哪年。结合以下两张图和sql，就能明白
hive> select year(date_sub(next_day('2015-01-01','monday'),4))*100 + weekofyear('2015-01-01');
201501
hive> select year(date_sub(next_day('2014-12-31','monday'),4))*100 + weekofyear('2014-12-31');
201501
hive> select year(date_sub(next_day('2016-01-01','monday'),4))*100 + weekofyear('2016-01-01');
201553
hive> select year(date_sub(next_day('2015-12-31','monday'),4))*100 + weekofyear('2015-12-31');
201553
