返回SQL中单个列中所有可能的值组合

Question

如何从数据库'x'的同一列中返回所有可能值组合的列表？例如,我有:

    col 1,
    1
    2
    3
    4

我想返回所有可能组合的列表,例如

    1,2
    1,3
    1,4
    2,3,
    2,4
    3,4

....

Answer 1

您没有说过您正在使用哪种RDBMS,或者您是否想要将组合限制为该组的2个元素.

以下是使用分层查询的Oracle答案:

SQL小提琴

Oracle 11g R2架构设置:

CREATE TABLE TEST ( COL ) AS
SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5;

查询1:

SELECT SUBSTR(SYS_CONNECT_BY_PATH(COL, ','), 2) AS combination
FROM TEST
CONNECT BY PRIOR COL < COL

结果:

| COMBINATION |
|-------------|
|           1 |
|         1,2 |
|       1,2,3 |
|     1,2,3,4 |
|       1,2,4 |
|         1,3 |
|       1,3,4 |
|         1,4 |
|           2 |
|         2,3 |
|       2,3,4 |
|         2,4 |
|           3 |
|         3,4 |
|           4 |

查询2:

SELECT SUBSTR(SYS_CONNECT_BY_PATH(COL, ','), 2) AS combination
FROM   TEST
WHERE  LEVEL = 2
CONNECT BY PRIOR COL < COL AND LEVEL <= 2

结果:

| COMBINATION |
|-------------|
|         1,2 |
|         1,3 |
|         1,4 |
|         2,3 |
|         2,4 |
|         3,4 |

和使用递归CTE的SQL Server版本:

SQL小提琴

MS SQL Server 2014架构设置:

CREATE TABLE TEST ( COL INT );

INSERT INTO TEST
          SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4;

查询1:

WITH cte ( combination, curr ) AS (
  SELECT CAST( t.COL AS VARCHAR(80) ),
         t.COL
  FROM   TEST t
  UNION ALL
  SELECT CAST( c.combination + ',' + CAST( t.col AS VARCHAR(1) ) AS VARCHAR(80) ),
         t.COL
  FROM   TEST t
         INNER JOIN
         cte c
         ON ( c.curr < t.COL )
)
SELECT combination FROM cte

结果:

| combination |
|-------------|
|           1 |
|           2 |
|           3 |
|           4 |
|         3,4 |
|         2,3 |
|         2,4 |
|       2,3,4 |
|         1,2 |
|         1,3 |
|         1,4 |
|       1,3,4 |
|       1,2,3 |
|       1,2,4 |
|     1,2,3,4 |

Answer 2

select concat(t1.id, ",", t2.id) from t t1 join t t2 on t1.id < t2.id;

可以在此处找到SQL小提琴示例.