LAG function and GROUP BY

Question

I have a table like this,

 event_id |          date          
----------+------------------------
  1703702 | 2013-06-25 07:50:57-04
  3197588 | 2013-06-25          


        

Answer 1

WITH diffs as (
    SELECT
        event_id,
        date - lag(date) over (partition BY event_id ORDER BY date) as difference
    FROM
        TABLE
)
SELECT
    event_id,
    array_agg( difference ) as all_diffs
FROM
    diffs
GROUP BY event_id;

Should work.