SQL和独特的n-coulmn组合

Question

在Oracle上有一种简单的方法来查询n个字段的唯一组合.我有一个非常简单的双场解决方案:

CREATE TABLE combinations AS
SELECT 1 AS n 
  FROM DUAL
UNION ALL
SELECT 2
  FROM DUAL;

查询独特的组合:

SELECT LEAST(x.a, x.b), 
       GREATEST(x.a,x.b) 
  FROM (SELECT c1.n a, 
               c2.n b 
          FROM combinations c1
    CROSS JOIN combinations c2
         WHERE c1.n <> c2.n) x
GROUP BY LEAST(x.a, x.b), GREATEST(x.a,x.b);

从该查询中,1,2和2,1被认为是相同的.不幸的是,它不适用于3场结构(例如1,2,3必须被认为与3,1,2相同,因为值的排序无关紧要).Oracle分析函数是否为此问题提供了合适的解决方案？你能推荐一些特定的Oracle分析功能吗？

Answer 1

您对2列的查询可以像这样重写:

SELECT
  c1.n,
  c2.n
FROM combinations c1
  INNER JOIN combinations c2 ON c1.n < c2.n

对于3列,您需要进行一些添加(以粗体突出显示):

SELECT
  c1.n,
  c2.n,
  c3.n
FROM combinations c1
  INNER JOIN combinations c2 ON c1.n < c2.n
  INNER JOIN combinations c3 ON c2.n < c3.n

我相信你现在可以很容易地猜到如何为更多列扩展它.