Find gap between two dates from table

Question

Hello All,
I want to find gap between two dates ,if there is no gap between two dates then it should return min(eff_dt) and max(end_dt) value
suppose below data in my item table
item_id    eff_dt           end_dt
10         20-jun-2012     25-jun-2012
10         26-jun-2012     28-jun-2012 There is no gap between two rows for item 10 then it should return rows like
item_id eff_dt end_dt
10 20-jun-2012 28-jun-2012
item_id    eff_dt           end_dt
12         20-jun-2012     25-jun-2012
12         27-jun-2012     28-jun-2012 There is gap between two rows for item 12 then it should return like
item_id eff_dt end_dt
12 20-jun-2012 25-jun-2012
12 27-jun-2012 28-jun-2012
I hv tried using below query but it giv null value for last row
SELECT   item_id, eff_dt, end_dt, end_dt + 1 AS newd,
         LEAD (eff_dt) OVER (PARTITION BY ctry_code, co_code, item_id ORDER BY ctry_code,
          co_code, item_id) AS LEAD,
         (CASE
             WHEN (end_dt + 1) =
                    LEAD (eff_dt) OVER (PARTITION BY ctry_code, co_code, item_id ORDER BY ctry_code,
                     co_code, item_id, eff_dt)
                THEN '1'
             ELSE '2'
          END
         ) AS new_num
  FROM item
   WHERE TRIM (item_id) = '802'
ORDER BY ctry_code, co_code, item_id, eff_dtI m using oracle 10g.
please any help is appreciate.
Thanks.

Answer 1

Use start of group method:
with sample_table as (
                      select 10 item_id,date '2012-6-20' start_dt,date '2012-6-25' end_dt from dual union all
                      select 10,date '2012-6-26',date '2012-6-26' from dual
select  item_id,
        min(start_dt) start_dt,
        max(end_dt) end_dt
  from  (
         select  item_id,
                 start_dt,
                 end_dt,
                 sum(start_of_group) over(partition by item_id order by start_dt) grp
           from  (
                  select  item_id,
                          start_dt,
                          end_dt,
                          case lag(end_dt) over(partition by item_id order by start_dt)
                            when start_dt - 1 then 0
                            else 1
                          end start_of_group
                    from  sample_table
  group by item_id,
           grp
  order by item_id,
           grp
   ITEM_ID START_DT  END_DT
        10 20-JUN-12 26-JUN-12
SQL> SY.