extract week number from date postgres

Question

I would like to extract the week number as:

2015-52 

from a date formatted as:

2015-12-27 

How can I perform this in postgres?

my weeks are calculated from monday to sunday.

Answer 1

To get the year and the week in a single character value, use to_char()

select to_char(current_date, 'IYYY-IW'); 

IW returns the year and the week number as defined in the ISO standard and IYYY returns the corresponding year (which might be the previous year).

If you need the year and the week number as numbers, use extract

select extract('isoyear' from current_date) as year,         extract('week' from current_date) as week; 

Answer 2

I have done like this

extract(week from cast(current_date as date)) extract(year from cast(current_date as date))