SQL & PL/SQL

This thread explains Tabibitosan method B-)

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1. What is Tabibitosan ? ?:|

"Tabibitosan" is Japanese language.
"Tabibitosan" is one of math problem.

http://www.manabinoba.com/index.cfm/7,757,33,1,html
http://yslibrary.cool.ne.jp/sansub1801.html

I do not know what "Tabibitosan" is called in English.
If you know, please teach me.

In Japanese -> English dictionary,
"Tabibito" means "pilgrim","viator" or "wayfaring man".

Japanese "Tabibitosan" book
http://www.amazon.co.jp/dp/4895243702

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2. What is basic usage of "Tabibitosan method" ? ?:|

"Tabibitosan method" is very effective when we want to collect Rows which are continued a lot of condition.

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For exsample1 (collect Rows continued Number)

create table Ex1 (NumVal primary key) as
select  1 from dual union
select  2 from dual union
select  3 from dual union
select  5 from dual union
select  6 from dual union
select  7 from dual union
select 10 from dual union
select 11 from dual union
select 12 from dual union
select 20 from dual union
select 21 from dual;

I will derive resultSet which collects Rows continued NumVal.

select min(NumVal),max(NumVal),count(*)
from (select NumVal,
      NumVal-Row_Number() over(order by NumVal)
      as disTance
      from Ex1)
group by disTance
order by min(NumVal);

MIN(NUMVAL) MAX(NUMVAL)   COUNT(*)
----------- ----------- ----------
          1           3          3
          5           7          3
         10          12          3
         20          21          2

In above solution,
I imagined that there are 2 people called X and A.
X always walks 1m. (Row_Number() over(order by NumVal))
A always walks more than 1m. (NumVal)

Then,I derived distance between X and A.
Then, I made group using these distance. (group by disTance)

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For exsample2 (collect Rows continued Days)

create table Ex2 (DateVal primary key) as
select date '2009-12-10' from dual union
select date '2009-12-11' from dual union
select date '2009-12-12' from dual union
select date '2009-12-16' from dual union
select date '2009-12-17' from dual union
select date '2009-12-20' from dual;

select min(DateVal),max(DateVal),count(*)
from (select DateVal,
      DateVal-Row_Number() over(order by DateVal)
      as disTance
      from Ex2)
group by disTance
order by min(DateVal);

MIN(DATE MAX(DATE   COUNT(*)
-------- -------- ----------
09-12-10 09-12-12          3
09-12-16 09-12-17          2
09-12-20 09-12-20          1