Missing numbers in a sequence

Question

I need to list all the missing numbers in a sequence. For example, in a table containing work orders, the work order numbers start from WO0001 and end at WO9999. In this some work order numbers like WO8001 may be missing. Can someone suggest me a way to extract these missing numbers?

Answer 1

This example uses the all_objects view and requires that you have at least as many rows in that view as in your work order table. If not, create a table with at least as many number and use that instead. The query in this example does not assume the lower and upper boundaries - it can be optimized a bit if those boundaries are hard-coded. Also, the fact that your work_order contains alpha characters (WO) had to be compensated for. Here is the idea (based on a Tom Kyte example, as usual):
sql>create table t (work_order) as
  2    select 'WO' || to_char(rownum, 'FM0000')
  3      from all_objects
  4     where rownum <= 9999;
Table created.
sql>delete from t
  2   where work_order in ('WO1000', 'WO5000', 'WO9000');
3 rows deleted.
sql>select 'WO' || missing_id missing_id
  2    from t,
  3         (select rownum + min_id - 1 missing_id
  4            from all_objects,
  5                 (select max(to_number(substr(work_order, 3))) max_id,
  6                         min(to_number(substr(work_order, 3))) min_id
  7                    from t)
  8           where rownum <= (select max(to_number(substr(work_order, 3))) -
  9                                   min(to_number(substr(work_order, 3))) + 1
10                              from t))
11   where missing_id = to_number(substr(work_order(+), 3))
12     and work_order is null;  
MISSING_ID
WO1000
WO5000
WO9000