SQL Query to Collapse Duplicate Values By Date Range

Question

I have a table with the following structure: ID, Month, Year, Value with values for one entry per id per month, most months have the same value.

I would like to crea

Answer 1

This one uses only one table scan and works across years. It's better though to model your month and year column as only one date datatype column:

SQL> create table tbl (id,month,year,value)
  2  as
  3  select 100,12,2007,80 from dual union all
  4  select 100,1,2008,80 from dual union all
  5  select 100,2,2008,80 from dual union all
  6  select 100,3,2008,90 from dual union all
  7  select 100,4,2008,80 from dual union all
  8  select 200,12,2007,50 from dual union all
  9  select 200,1,2008,50 from dual union all
 10  select 200,2,2008,40 from dual union all
 11  select 200,3,2008,50 from dual union all
 12  select 200,4,2008,50 from dual union all
 13  select 200,5,2008,50 from dual
 14  /

Tabel is aangemaakt.

SQL> select id
  2       , mod(min(year*12+month-1),12)+1 startmonth
  3       , trunc(min(year*12+month-1)/12) startyear
  4       , mod(max(year*12+month-1),12)+1 endmonth
  5       , trunc(max(year*12+month-1)/12) endyear
  6       , value
  7    from ( select id
  8                , month
  9                , year
 10                , value
 11                , max(rn) over (partition by id order by year,month) maxrn
 12             from ( select id
 13                         , month
 14                         , year
 15                         , value
 16                         , case lag(value) over (partition by id order by year,month)
 17                           when value then null
 18                           else rownum
 19                           end rn
 20                      from tbl
 21                  ) inner
 22         )
 23   group by id
 24       , maxrn
 25       , value
 26   order by id
 27       , startyear
 28       , startmonth
 29  /

        ID STARTMONTH  STARTYEAR   ENDMONTH    ENDYEAR      VALUE
---------- ---------- ---------- ---------- ---------- ----------
       100         12       2007          2       2008         80
       100          3       2008          3       2008         90
       100          4       2008          4       2008         80
       200         12       2007          1       2008         50
       200          2       2008          2       2008         40
       200          3       2008          5       2008         50

6 rijen zijn geselecteerd.

Regards, Rob.