SQL All Possible Round Robin Combinations between two Tables

问题

given table:

create table Person( Name varchar(100) )

where Name is unique for all Persons

What SQL query can generate all possible n!/((n-2)!2!) round robin combinations?

It is assumed that the cardinality of Person is ALWAYS equal to 4

Example Person = {'Anna','Jerome','Patrick','Michael')

Output:

Anna, Jerome
Anna, Patrick
Anna, Michael
Jerome, Patrick
Jerome, Michael
Patrick, Michael

Any help would be appreciated. Thanks!

Here's my answer (I used oracle SQL):

select P1.NAME PERSON1, P2.NAME PERSON2
  from (select rownum RNUM, NAME
        from PERSON) P1,
       (select rownum RNUM, NAME
          from PERSON) P2
 where P1.RNUM < P2.RNUM

回答1:

Here are two solutions for the problem

SELECT  t1.Name + ',' +  t2.Name AS NamesCombination
FROM Person t1
INNER JOIN Person t2
ON t1.Name < t2.Name

OR (Oracle 11i R2+)

WITH NamesCombination AS 
( 
    SELECT  1 AS Cntr
            ,Name 
            , CAST(Name AS VARCHAR(MAX))AS NamesCombinations
    FROM Person 
    UNION ALL 
    SELECT  
        nc.Cntr+1
        ,p.Name 
        ,nc.NamesCombinations + ',' +  CAST(p.Name AS VARCHAR(MAX))                      
    FROM Person AS p JOIN NamesCombination nc ON p.Name < nc.Name
    WHERE nc.Cntr < 2  
)
SELECT NamesCombinations
FROM NamesCombination
WHERE Cntr  = 2

回答2:

select P1.NAME PERSON1, P2.NAME PERSON2
  from (select rownum RNUM, NAME
        from PERSON) P1,
       (select rownum RNUM, NAME
          from PERSON) P2
 where P1.RNUM < P2.RNUM

回答3:

Note that this is TSQL (Sql Server) syntax. I know that Oracle supports windowing functions, particularly row_number(), which is necessary for this solution.

It shouldn't be too hard to get this to work in Oracle with some trial and error

select p1.name, p2.name
from 
(
    select name,  row_number() over(order by name) as rownumber 
    from person
) p1
inner join
(
    select name, row_number() over(order by name) as rownumber
    from person
) p2
on p1.name <> p2.name
and p1.rownumber > p2.rownumber
order by 1

row_number assigns a row number to each row. You then need to join, as suggested before, with the additional join clause of p1.rownumber > p2.rownumber

来源：https://stackoverflow.com/questions/13372232/sql-all-possible-round-robin-combinations-between-two-tables

标签

sql

Oracle

combinations

round-robin