问题
2016-01-01 is the week 1 of 2016, but also is the week 53 of 2015.
When I run SELECT DATE_PART(w, '2016-01-01') it returns 53, but when I run SELECT DATE_PART(w, '2016-01-04') it returns 1.
Most probably this is happening because Redshift sets Monday as the day 1 of the week, and not Sunday, as it should be.
Not sure if this will solve the problem, but what I need is to make 2016-01-01 as week 1 and from 2016-01-03 to 2016-01-09 as week 2 and so on...
回答1:
Create a custom function with this case statement or use it in your SQL statements:
case when DATE_PART('W', dt)>=51 and EXTRACT(DOY FROM dt) < 8 then 1 else DATE_PART('W', dt)+1 end week_no
It will start counting weeks on Jan 1st.
http://sqlfiddle.com/#!15/ccb90/9
来源：https://stackoverflow.com/questions/35416474/how-to-set-datefirst-equal-to-sunday-in-amazon-redshift