Looking for gaps (SQL, not PL/SQL)

Question

Hi,
This is a SQL (not PL/SQL) question.
Let's say I have the following table:
COLtype          COLnumber
AA               1
AA               2
AA               4
AA               5
BB               1
BB               2
BB               3
BB               5
CC               1
CC               5
How do I find all gaps? I expect a result:
COLtype          COLnumber
AA               3
BB               4
CC               2
CC               3
CC               4
I tried to use query:
SELECT COLnumber + 1, COLtype FROM table a1
WHERE NOT EXISTS (
SELECT NULL FROM table a2
     WHERE
a1.COLtype = a2.COLtype
and (a2.COLnumber = a1.COLnumber + 1)
but I received as result:
COLtype          COLnumber
AA               3
AA               6
BB               4
BB               6
CC               2
CC               3
CC               4
CC               6
Any other solutions, ideas?
Thanks in advance!
Gaspar
Edited by: 985540 on 2013-02-01 02:59

Answer 1

First let define gaps. If we have:
COLtype COLnumber
AA      3
AA      4Are:
COLtype COLnumber
AA      1
AA      2missing? If so is there an assumption COLnumber always starts with 1 or we just looking for gaps between existing numbers? For now I'll assume we are looking for gaps between existing numbers. Then:
with t as (
           select  coltype,
                   colnumber,
                   lag(colnumber,1,colnumber - 1)
                     over(
                          partition by coltype
                          order by colnumber
                         ) prev_colnumber
             from  tbl
select  coltype,
        colnumber - column_value colnumber
  from  t,
        table(
              cast(
                   multiset(
                            select  level
                              from  dual
                              connect by level < colnumber - prev_colnumber
                   as sys.OdciNumberList
  where colnumber - prev_colnumber > 1
  order by coltype,
           colnumber
CO  COLNUMBER
AA          3
BB          4
CC          2
CC          3
CC          4
SQL> explain plan for
  2  with t as (
  3             select  coltype,
  4                     colnumber,
  5                     lag(colnumber,1,colnumber - 1)
  6                       over(
  7                            partition by coltype
  8                            order by colnumber
  9                           ) prev_colnumber
10               from  tbl
11            )
12  select  coltype,
13          colnumber - column_value colnumber
14    from  t,
15          table(
16                cast(
17                     multiset(
18                              select  level
19                                from  dual
20                                connect by level < colnumber - prev_colnumber
21                             )
22                     as sys.OdciNumberList
23                    )
24               )
25    where colnumber - prev_colnumber > 1
26    order by coltype,
27             colnumber
28  /
Explained.
SQL> @?\rdbms\admin\utlxpls
PLAN_TABLE_OUTPUT
Plan hash value: 1739894384
| Id  | Operation                            | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT                     |      | 81680 |  2552K|       |   991   (1)| 00:00:12 |
|   1 |  SORT ORDER BY                       |      | 81680 |  2552K|  3216K|   991   (1)| 00:00:12 |
|   2 |   NESTED LOOPS                       |      | 81680 |  2552K|       |   277   (1)| 00:00:04 |
|*  3 |    VIEW                              |      |    10 |   300 |       |     4  (25)| 00:00:01 |
|   4 |     WINDOW SORT                      |      |    10 |   170 |       |     4  (25)| 00:00:01 |
|   5 |      TABLE ACCESS FULL               | TBL  |    10 |   170 |       |     3   (0)| 00:00:01 |
PLAN_TABLE_OUTPUT
|   6 |    COLLECTION ITERATOR SUBQUERY FETCH|      |  8168 | 16336 |       |    27   (0)| 00:00:01 |
|*  7 |     CONNECT BY WITHOUT FILTERING     |      |       |       |       |            |          |
|   8 |      FAST DUAL                       |      |     1 |       |       |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   3 - filter("COLNUMBER"-"PREV_COLNUMBER">1)
   7 - filter(LEVEL<:B1-:B2)
PLAN_TABLE_OUTPUT
Note
   - dynamic sampling used for this statement (level=2)
25 rows selected.
SQL> SY.