Postgresql: using 'with clause' to iterate over a range of dates

问题

I have a database table that contains a start visdate and an end visdate. If a date is within this range the asset is marked available. Assets belong to a user. My query takes in a date range (start and end date). I need to return data so that for a date range it will query the database and return a count of assets for each day in the date range that assets are available.

I know there are a few examples, I was wondering if it's possible to just execute this as a query/common table expression rather than using a function or a temporary table. I'm also finding it quite complicated because the assets table does not contain one date which an asset is available on. I'm querying a range of dates against a visibility window. What is the best way to do this? Should I just do a separate query for each day in the date range I'm given?

Asset Table
StartvisDate Timestamp
EndvisDate   Timestamp
ID           int

User Table
ID

User & Asset Join table
UserID
AssetID


Date       | Number of Assets Available | User
11/11/14              5                   UK
12/11/14              6                   Greece
13/11/14              4                   America
14/11/14              0                   Italy

回答1:

You need to use a set returning function to generate the needed rows. See this related question:

SQL/Postgres datetime division / normalizing

Example query 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,
       count(data.id)
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)
group by data.id

 id | count 
----+-------
  1 |     2
  2 |     1
(2 rows)

You'll want to convert it to using ranges instead, and adapt it to your own schema and data, but it's basically the same kind of query as the one you want.

来源：https://stackoverflow.com/questions/27400560/postgresql-using-with-clause-to-iterate-over-a-range-of-dates

标签

postgresql

common-table-expression