How do I return a list of all possible combinations of values from within the same single column of database 'x'? For example I have:
col 1,
1
2
3
4
And I would like to return a list of all possible combinations like,
1,2
1,3
1,4
2,3,
2,4
3,4
....
答案 0 :(得分:9)
You've not said which RDBMS you are using or whether you want to limit the combinations to just 2 elements of the set.
Here is an Oracle answer using hierarchical queries:
Oracle 11g R2 Schema Setup:
CREATE TABLE TEST ( COL ) AS
SELECT LEVEL FROM DUAL CONNECT BY LEVEL < 5;
Query 1:
SELECT SUBSTR(SYS_CONNECT_BY_PATH(COL, ','), 2) AS combination
FROM TEST
CONNECT BY PRIOR COL < COL
| 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 |
Query 2:
SELECT SUBSTR(SYS_CONNECT_BY_PATH(COL, ','), 2) AS combination
FROM TEST
WHERE LEVEL = 2
CONNECT BY PRIOR COL < COL AND LEVEL <= 2
| COMBINATION |
|-------------|
| 1,2 |
| 1,3 |
| 1,4 |
| 2,3 |
| 2,4 |
| 3,4 |
And an SQL Server version using a recursive CTE:
MS SQL Server 2014 Schema Setup:
CREATE TABLE TEST ( COL INT );
INSERT INTO TEST
SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4;
Query 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
| 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 |
答案 1 :(得分:7)
select concat(t1.id, ",", t2.id) from t t1 join t t2 on t1.id < t2.id;
An SQL Fiddle example can be found here.