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Message from discussion Reduce To Ranges aggregate function
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Charles Hooper  
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 More options Oct 21 2006, 8:53 am
Newsgroups: comp.databases.oracle.misc
From: "Charles Hooper" <hooperc2...@yahoo.com>
Date: 21 Oct 2006 05:53:18 -0700
Local: Sat, Oct 21 2006 8:53 am
Subject: Re: Reduce To Ranges aggregate function
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Michel Cadot wrote:
> "Mike King" <emai...@excite.com> a écrit dans le message de news: 12jfcsjsafvm...@corp.supernews.com...
> | Has someone ready created an aggregate function that reduces a set of
> | numbers to a reduced form.  I'm writing some middleware software that needs
> | to know the IDs of some tuples but the query could return tens or thousands
> | of tuples.  I'm thinking if there were an aggregate function that would
> | reduce the network traffic.
> |
> | select reduced_to_ranges(id)
> | from some_large_table
> | where some_field = some_value
> |
> | ID
> | ----
> | 1
> | 2
> | 3
> | 4
> | 5
> | 11
> | 12
> | 45
> |
> | Reduced form: 1-5,11-12,45
> |
> |

> SQL> select id from t order by id;
>         ID
> ----------
>          1
>          2
>          3
>          4
>          5
>         11
>         12
>         45

> 8 rows selected.

> SQL> col Range format a20
> SQL> with
>   2    step1 as (
>   3      select id,
>   4             case
>   5             when nvl(lag(id) over (order by id),-1) != id-1 then id
>   6             end grp
>   7      from t),
>   8    step2 as (
>   9      select id,
>  10             max(grp) over (order by id) grp
>  11      from step1
>  12    )
>  13  select min(id)||decode(min(id),max(id),'','-'||max(id)) "Range"
>  14  from step2
>  15  group by grp
>  16  /
> Range
> --------------------
> 1-5
> 11-12
> 45

> 3 rows selected.

> Regards
> Michel Cadot

I guess that I have a bit of difficulty understanding what the OP was
wanting.  That is an interesting solution that you posted Michel.  I am
not sure that I would have tried to use analytical functions to solve
the problem, but your example is clever.

If we can make the assumption that the OP was looking for a way to
group the numbers 1-10, 11-20, 21-30, 31-40, 41-50, a much simplier
approach is as follows:

CREATE TABLE T (ID NUMBER(22));
INSERT INTO T VALUES (1);
INSERT INTO T VALUES (2);
INSERT INTO T VALUES (3);
INSERT INTO T VALUES (4);
INSERT INTO T VALUES (5);
INSERT INTO T VALUES (11);
INSERT INTO T VALUES (12);
INSERT INTO T VALUES (45);

SELECT
  MIN(ID)||DECODE(MAX(ID),MIN(ID),'','-'||MAX(ID)) RANGE
FROM
  T
GROUP BY
  TRUNC((ID-1)/10)
ORDER BY
  TRUNC((ID-1)/10);

RANGE
======
1-5
11-12
45

SELECT

MAX(DECODE(ROWNUM,1,RANGE,''))||MAX(DECODE(ROWNUM,2,','||RANGE,''))||MAX(DE CODE(ROWNUM,3,','||RANGE,''))||MAX(DECODE(ROWNUM,4,','||RANGE,''))||MAX(DEC ODE(ROWNUM,5,','||RANGE,''))||MAX(DECODE(ROWNUM,6,','||RANGE,''))
REDUCED_FORM
FROM
  (SELECT
    MIN(ID)||DECODE(MAX(ID),MIN(ID),'','-'||MAX(ID)) RANGE
  FROM
    T
  GROUP BY
    TRUNC((ID-1)/10)
  ORDER BY
    TRUNC((ID-1)/10)) T;

REDUCED_FORM
============
1-5,11-12,45

Looking at the OP's suggested SQL statement:

> | select reduced_to_ranges(id)
> | from some_large_table
> | where some_field = some_value

SELECT
  ID,
  TRUNC((ID-1)/10) RANGE
FROM
  T;

        ID      RANGE
========== ==========
         1          0
         2          0
         3          0
         4          0
         5          0
        11          1
        12          1
        45          4

INSERT INTO T VALUES (100);

SELECT
  TRUNC((ID-1)/10) RANGE
FROM
  T
WHERE
  ID=100;

RANGE
==========
 9

Charles Hooper
PC Support Specialist
K&M Machine-Fabricating, Inc.


 
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