Splitting up an interval in weeks in Postgres

Question

Here goes a yet another SQL question about dates…

I'm building a calendaring application using PHP and Postgres that would display events spanning days, weeks or possibly months. Each event has a start date and an end date, and selecting them by range is not a problem; however, it would be useful for me if Postgres could split multi-week events at the first day of each week. I've been told it can be done using GROUP BY and EXTRACT, but I'm not good enough with SQL to understand how.

The question is: can this be done, and what would the precise query look like? Currently I'm using SELECT * FROM events WHERE (range) OVERLAPS (range); and then doing the splitting in PHP, but it's clearly not optimal.

Answer 1

You can use the Postgres function generate_series. In 8.3 and earlier, do things like

select current_date + s.a as dates from generate_series(0,14,7) as s(a);

In 8.4, you can also do

SELECT * FROM generate_series('2008-03-01 00:00'::timestamp,
                              '2008-03-04 12:00', '10 hours');

Answer 2

First of all - it would be good to show some sample input and output of the query you'd like us to help you with - I, for example, don't really get what it is that you need.

Also - you might find OVERLAPS to be suboptimal, as it's not indexable. Instead you might want to use the method I described in this blog post.