Question

I want to get the right week number.

Using the to_char function, the function enumerate the week starting with mondey, but i want to get the week number considering that a week start on saturday.

Here is an example:

SELECT to_char('05-01-2013'::date,'daydd-mm-yyyy') as date_char, to_char('05-01-2013'::date,'IW') as week_number

Result:

"saturday 05-01-2013";"01"   

And should be:

"saturday 05-01-2013";"02"  

Is there any way to get it?

Config info: Postgresql 9.2 under Windows 7

Answer 1

This will give the correct result:

with first_friday as (
    select extract(doy from min(a)::date) ff
    from generate_series('2013-01-01'::date, '2013-01-07', '1 day') s(a)
    where extract(dow from a) = 5
)
select
    to_char(a, 'day'),
    a::date "day",
    floor((extract(doy from a) - (select ff from first_friday) - 1) / 7) + 2 week_number
from generate_series('2013-01-01'::date, '2013-01-31', '1 day') s(a)
;
  to_char  |    day     | week_number 
-----------+------------+-------------
 tuesday   | 2013-01-01 |           1
 wednesday | 2013-01-02 |           1
 thursday  | 2013-01-03 |           1
 friday    | 2013-01-04 |           1
 saturday  | 2013-01-05 |           2
 sunday    | 2013-01-06 |           2
 monday    | 2013-01-07 |           2
 tuesday   | 2013-01-08 |           2
 wednesday | 2013-01-09 |           2
 thursday  | 2013-01-10 |           2
 friday    | 2013-01-11 |           2
 saturday  | 2013-01-12 |           3
 sunday    | 2013-01-13 |           3
 monday    | 2013-01-14 |           3
 tuesday   | 2013-01-15 |           3
 wednesday | 2013-01-16 |           3
 thursday  | 2013-01-17 |           3
 friday    | 2013-01-18 |           3
 saturday  | 2013-01-19 |           4
 sunday    | 2013-01-20 |           4
 monday    | 2013-01-21 |           4
 tuesday   | 2013-01-22 |           4
 wednesday | 2013-01-23 |           4
 thursday  | 2013-01-24 |           4
 friday    | 2013-01-25 |           4
 saturday  | 2013-01-26 |           5
 sunday    | 2013-01-27 |           5
 monday    | 2013-01-28 |           5
 tuesday   | 2013-01-29 |           5
 wednesday | 2013-01-30 |           5
 thursday  | 2013-01-31 |           5