用这个公式,A1换成你的日期单元格，就可以避免跨年的问题了。

=INARRAY(WEEK(A1), UNIQUEARRAY(MAPARRAY(RANGE(DATEINMONTH(A1, 1), DATEINMONTH(A1, -1)), WEEK(ITEM))))

获取日期在当月中是第几周-https://help.fanruan.com/finereport/doc-view-2596.html

有个问题，那你们是怎么定义跨月的。上个月一些周末到下个月，周日在下个月，要怎么算？

case 

when (create_date) is NULL then ''

when cast(day(create_date) as float)/7=1 and cast(day(create_date) as int)%7=0 then CAST(MONTH(create_date) as VARCHAR(10))+ '月第1周'

when cast(day(create_date) as float)/7=2 and cast(day(create_date) as int)%7=0 then CAST(MONTH(create_date) as VARCHAR(10))+'月第2周'

when cast(day(create_date) as float)/7=3 and cast(day(create_date) as int)%7=0 then CAST(MONTH(create_date) as VARCHAR(10))+'月第3周'

when cast(day(create_date) as float)/7=4 and cast(day(create_date) as int)%7=0 then CAST(MONTH(create_date) as VARCHAR(10))+'月第4周'

when cast(day(create_date) as float)/7<1 then CAST(MONTH(create_date) as VARCHAR(10))+'月第1周'

when cast(day(create_date) as float)/7>1 and cast(day(create_date) as float)/7<2 then CAST(MONTH(create_date) as VARCHAR(10))+'月第2周'

when cast(day(create_date) as float)/7>2 and cast(day(create_date) as float)/7<3 then CAST(MONTH(create_date) as VARCHAR(10))+'月第3周'

when cast(day(create_date) as float)/7>3 and cast(day(create_date) as float)/7<4 then CAST(MONTH(create_date) as VARCHAR(10))+'月第4周'

else CAST(MONTH(create_date) as VARCHAR(10))+'月第5周'

end as week

这个是从1号开始，一周7天的算法。sql server，具体的看着修改。