问题
I have this activity table
+--------------+------------------+
| Field | Type |
+--------------+------------------+
| id | int(11) unsigned |
| start_date | timestamp |
| end_date | timestamp |
| ... | |
+--------------+------------------+
I need a view which groups these activities by start_date by DAY, but in such a way that, if the end_date is not in the same day as start_date, the view contain the entry again but with the start_date set to 00:00 of the next day.. (and so on, repeated as many times as needed until the start_date is in the same day as the end_date)
As an example:
if the activity table contains:
+--------------+----------------------------+----------------------------+
| id | start_date | end_date |
+--------------+----------------------------+----------------------------+
| 1 | 2014-12-02 14:12:00+00 | 2014-12-03 06:45:00+00 |
| 2 | 2014-12-05 15:25:00+00 | 2014-12-05 07:29:00+00 |
+--------------+----------------------------+----------------------------+
The view should contain:
+--------------+----------------------------+----------------------------+
| activity_id | start_date | end_date |
+--------------+----------------------------+----------------------------+
| 1 | 2014-12-02 14:12:00+00 | 2014-12-02 23:59:59+00 |
| 1 | 2014-12-03 00:00:00+00 | 2014-12-03 06:45:00+00 |
| 2 | 2014-12-05 15:25:00+00 | 2014-12-05 07:29:00+00 |
+--------------+----------------------------+----------------------------+
Any help would be greatly appreciated!
PS: I'm using postgresql
回答1:
To get the needed rows, start by using a set returning function along with a lateral join. From there, use CASE statements and date arithmetics to pull out the relevant values.
Here's an example to get you started:
with data as (
select id, start_date, end_date
from (values
(1, '2014-12-02 14:12:00+00'::timestamptz, '2014-12-03 06:45:00+00'::timestamptz),
(2, '2014-12-05 15:25:00+00'::timestamptz, '2014-12-05 07:29:00+00'::timestamptz)
) as rows (id, start_date, end_date)
)
select data.id,
case days.d = date_trunc('day', data.start_date)
when true then data.start_date
else days.d
end as start_date,
case days.d = date_trunc('day', data.end_date)
when true then data.end_date
else days.d + interval '1 day' - interval '1 sec'
end as end_date
from data
join generate_series(
date_trunc('day', data.start_date),
date_trunc('day', data.end_date),
'1 day'
) as days (d)
on days.d >= date_trunc('day', data.start_date)
and days.d <= date_trunc('day', data.end_date)
id | start_date | end_date
----+------------------------+------------------------
1 | 2014-12-02 15:12:00+01 | 2014-12-02 23:59:59+01
1 | 2014-12-03 00:00:00+01 | 2014-12-03 07:45:00+01
2 | 2014-12-05 16:25:00+01 | 2014-12-05 08:29:00+01
(3 rows)
As an aside, depending on what you're doing, it might make more sense for you to use a date range:
with data as (
select id, start_date, end_date
from (values
(1, '2014-12-02 14:12:00+00'::timestamptz, '2014-12-03 06:45:00+00'::timestamptz),
(2, '2014-12-05 07:25:00+00'::timestamptz, '2014-12-05 15:29:00+00'::timestamptz)
) as rows (id, start_date, end_date)
)
select data.id,
tstzrange(data.start_date, data.end_date)
from data;
id | tstzrange
----+-----------------------------------------------------
1 | ["2014-12-02 15:12:00+01","2014-12-03 07:45:00+01")
2 | ["2014-12-05 08:25:00+01","2014-12-05 16:29:00+01")
(2 rows)
来源：https://stackoverflow.com/questions/27398934/sql-postgres-datetime-division-normalizing