Hur kan jag effektivt söka efter sammanhängande uppsättningar datum i min datamängd?

Här är ett exempel på hur man gör en sådan fråga:

SQL> create table t (site_id,start_date,end_date)
  2  as
  3  select 1, date '2008-10-01', date '2008-10-02' from dual union all
  4  select 1, date '2008-10-02', date '2008-10-03' from dual union all
  5  select 1, date '2008-10-03', date '2008-10-30' from dual union all
  6  select 1, date '2008-10-30', date '2008-10-31' from dual union all
  7  select 2, date '2008-10-01', date '2008-10-02' from dual union all
  8  select 2, date '2008-10-02', date '2008-10-03' from dual union all
  9  select 2, date '2008-10-03', date '2008-10-04' from dual union all
 10  select 2, date '2008-10-04', date '2008-10-05' from dual union all
 11  select 2, date '2008-10-05', date '2008-10-06' from dual union all
 12  select 2, date '2008-10-06', date '2008-10-07' from dual union all
 13  select 2, date '2008-10-07', date '2008-10-08' from dual union all
 14  select 2, date '2008-10-08', date '2008-10-09' from dual union all
 15  select 2, date '2008-10-09', date '2008-10-10' from dual union all
 16  select 2, date '2008-10-10', date '2008-10-11' from dual union all
 17  select 2, date '2008-10-11', date '2008-10-12' from dual union all
 18  select 2, date '2008-10-12', date '2008-10-13' from dual union all
 19  select 2, date '2008-10-13', date '2008-10-14' from dual union all
 20  select 2, date '2008-10-14', date '2008-10-15' from dual union all
 21  select 2, date '2008-10-15', date '2008-10-16' from dual union all
 22  select 2, date '2008-10-16', date '2008-10-17' from dual union all
 23  select 2, date '2008-10-17', date '2008-10-18' from dual union all
 24  select 2, date '2008-10-18', date '2008-10-19' from dual union all
 25  select 2, date '2008-10-19', date '2008-10-20' from dual union all
 26  select 3, date '2008-10-01', date '2008-10-02' from dual union all
 27  select 3, date '2008-10-02', date '2008-10-03' from dual union all
 28  select 3, date '2008-10-03', date '2008-10-04' from dual union all
 29  select 3, date '2008-10-04', date '2008-10-05' from dual union all
 30  select 3, date '2008-10-05', date '2008-10-06' from dual union all
 31  select 3, date '2008-10-06', date '2008-10-07' from dual union all
 32  select 3, date '2008-10-07', date '2008-10-08' from dual union all
 33  select 3, date '2008-10-08', date '2008-10-09' from dual union all
 34  select 3, date '2008-10-09', date '2008-10-10' from dual union all
 35  select 3, date '2008-10-30', date '2008-10-31' from dual
 36  /

Tabel is aangemaakt.

Och sedan frågan:

SQL> select site_id
  2       , min(start_date) contiguous_start_date
  3       , max(end_date) contiguous_end_date
  4       , count(*) number_of_contiguous_records
  5    from ( select site_id
  6                , start_date
  7                , end_date
  8                , max(rn) over (partition by site_id order by start_date) maxrn
  9             from ( select site_id
 10                         , start_date
 11                         , end_date
 12                         , case lag(end_date) over (partition by site_id order by start_date)
 13                             when start_date then null
 14                             else rownum
 15                           end rn
 16                      from t
 17                  )
 18          )
 19   group by site_id
 20       , maxrn
 21   order by site_id
 22       , contiguous_start_date
 23  /

Och resultaten:

   SITE_ID CONTIGUOUS_START_DA CONTIGUOUS_END_DATE NUMBER_OF_CONTIGUOUS_RECORDS
---------- ------------------- ------------------- ----------------------------
         1 01-10-2008 00:00:00 31-10-2008 00:00:00                            4
         2 01-10-2008 00:00:00 20-10-2008 00:00:00                           19
         3 01-10-2008 00:00:00 10-10-2008 00:00:00                            9
         3 30-10-2008 00:00:00 31-10-2008 00:00:00                            1

4 rijen zijn geselecteerd.

Hälsningar, Rob.