sql - Can you define a custom "week" in PostgreSQL? -


i know in order extract week of of given year can use:

select extract(week timestamp '2014-02-16 20:38:40');

however, trying group weeks in bit of odd format. start of week begin on mondays @ 4am , conclude following monday @ 3:59:59am.

ideally, create query provides start , end date, groups total sales period weeks laid out above.

example:

select    (some custom week date),    sum(sales) salestable     startdate between 'date 1' , 'date 2'

note: not looking change extract() function, rather create query pull following sample table , output sample results.

if date 1 in query '2014-07-01' , date 2 '2014-08-18':

sample table:

itemid | timesold            | price ------------------------------------ 1      | 2014-08-13 09:13:00 | 12.45 2      | 2014-08-15 12:33:00 | 20.00 3      | 2014-08-05 18:33:00 | 10.00 4      | 2014-07-31 04:00:00 | 30.00

ideal sample output:

weekbegin           |   pricetotal ---------------------------------- 2014-07-28 04:00:00 | 30.00 2014-08-04 04:00:00 | 10.00 2014-08-11 04:00:00 | 32.45

this postgres requested in title.

select date_trunc('week', time_sold - interval '4h')                                     + interval '4h' week_begin       ,sum(price) price_total   tbl  time_sold >= '2014-07-01 0:0'::timestamp ,    time_sold <  '2014-08-19 0:0'::timestamp -- start of next day group  1 order  1;

produces desired output exactly.

sql fiddle (extended row shows difference).

explain

  • date_trunc() superior tool here. not interested in week numbers, in actual timestamps.

  • the trick subtract 4 hours selected timestamps before extracting week - thereby shifting time frame towards earlier border of iso week.

  • to produce display desire, add 4 hours truncated timestamps.

  • but apply where condition on unmodified timestamps. also, never use between timestamps, have fractional digits. use where conditions presented above. compare:

  • operating data type timestamp, i.e. (shifted) "weeks" according current time zone. additional considerations apply timestamptz. more:


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