How to get week start and end date string in PostgreSQL? - sql

Question

I am using PostgreSQL 8.3. I have a table like this:
id regist_time result
-----------------------------------
1 2012-07-09 15:00:08 3
2 2012-07-25 22:24:22 7
4 2012-07-07 22:24:22 8
regist_time's data type is timestamp.
I need to find a week time interval(start to end)
and sum(result) as num.
I want to get the result as:
week num
---------------------------------
7/1/2012-7/7/2012 10
7/8/2012-7/14/2012 5
7/15/2012-7/21/2012 3
7/22/2012-7/28/2012 11
I can get the week number just in this year:
SELECT id,regis_time, EXTRACT(WEEK FROM regis_time) AS regweek
FROM tba
The key part is
EXTRACT(WEEK FROM regis_time)
extract function can only get the week number in this year, how can I get start time to end time in one week?

Answer 1

You can use date_trunc('week', ...).
For example:
SELECT date_trunc('week', '2012-07-25 22:24:22'::timestamp);
-> 2012-07-23 00:00:00
Then, you can convert this into a date, if you're not interested in a start time.
To get the end date too:
SELECT date_trunc('week', '2012-07-25 22:24:22'::timestamp)::date
|| ' '
|| (date_trunc('week', '2012-07-25 22:24:22'::timestamp)+ '6 days'::interval)::date;
-> 2012-07-23 2012-07-29
(I've used the default formatting here, you can of course adapt this to use MM/DD/YYYY.)
Note that, if you want to make comparisons on timestamps, instead of using (date_trunc('week', ...) + '6 days'::interval, you might want to add an entire week and use a strict comparison for the end of the week.
This will exclude y timestamps on the last day of the week (since the cut-off time is midnight on the day).
date_trunc('week', x)::date <= y::timestamp
AND y::timestamp <= (date_trunc('week', x) + '6 days'::interval)::date
This will include them:
date_trunc('week', x)::date <= y::timestamp
AND y::timestamp < (date_trunc('week', x) + '1 week'::interval)
(That's in the rare cases when you can't use date_trunc on y directly.)
If your week starts on a Sunday, replacing date_trunc('week', x)::date with date_trunc('week', x + '1 day'::interval)::date - '1 day'::interval should work.

Answer 2

select date_trunc('week', regist_time)::date || ' - ' ||
(date_trunc('week', regist_time) + '6 days') ::date as Week,
sum(result) Total
from YourTable
group by date_trunc('week', regist_time)
order by date_trunc('week', regist_time)
See proof of concept at SQLFiddle: http://sqlfiddle.com/#!1/9e821/1

Answer 3

This can help, a query to get all days of current week.
select cast(date_trunc('week', current_date) as date) + i
from generate_series(0,6) i
2015-08-17
2015-08-18
2015-08-19
2015-08-20
2015-08-21
To get week start and end date (as 0 for Monday and 4 for Friday):
select cast(date_trunc('week', current_date) as date) + 0 || '-->' || cast(date_trunc('week', current_date) as date) + 4;
2015-08-17-->2015-08-21

Answer 4

It is
select to_date('2015-07', 'IYYY-IW');
use it in postgres
it will return
2015-02-09

Answer 5

If you want to get week start and end date with week start day is any day in the week (Monday, Tuesday, ...). You can use this way:
day_of_week_index mapping:
{
'monday': 1,
'tuesday': 2,
'wednesday': 3,
'thursday': 4,
'friday': 5,
'saturday': 6,
'sunday': 7
}
Query template:
SELECT
concat(
CASE
WHEN extract(ISODOW FROM datetime_column) < day_of_week_index THEN cast(date_trunc('week', datetime_column) AS date) - 8 + day_of_week_index
ELSE cast(date_trunc('week', datetime_column) AS date) - 1 + day_of_week_index
END, ' - ',
CASE
WHEN extract(ISODOW FROM datetime_column) < day_of_week_index THEN cast(date_trunc('week', datetime_column) AS date) - 8 + day_of_week_index + 6
ELSE cast(date_trunc('week', datetime_column) AS date) - 1 + day_of_week_index + 6
END)
FROM table_name;
Example:
Get week start and end date with week start day is Tuesday:
SELECT
concat(
CASE
WHEN extract(ISODOW FROM TIMESTAMP '2021-12-01 03:00:00') < 2 THEN cast(date_trunc('week', TIMESTAMP '2021-12-01 03:00:00') AS date) - 8 + 2
ELSE cast(date_trunc('week', TIMESTAMP '2021-12-01 03:00:00') AS date) - 1 + 2
END, ' - ',
CASE
WHEN extract(ISODOW FROM TIMESTAMP '2021-12-01 03:00:00') < 2 THEN cast(date_trunc('week', TIMESTAMP '2021-12-01 03:00:00') AS date) - 8 + 2 + 6
ELSE cast(date_trunc('week', TIMESTAMP '2021-12-01 03:00:00') AS date) - 1 + 2 + 6
END);
=> Result:
2021-11-30 - 2021-12-06
Note: You can change the day_of_week_index following the above mapping to determine the week start day (Monday, Tuesday, ..., Sunday)