sql - 按多列分组并将结果作为单独列中的数组

Question

我有如下表格:

| col_A | col_B |
|-------|-------|
| 1     | 1     |
| 1     | 2     |
| 1     | 3     |
| 2     | 1     |
| 2     | 2     |
| 2     | 3     |
| 3     | 1     |
| 3     | 2     |

我想将结果分组并连接成一个数组，如下所示:

| col_A | col_B |
|-------|-------|
| 1,2   | 1,2,3 |
| 3     |  1,2  |

我尝试编写一个查询:

SELECT col_A, array_agg(col_B ORDER BY col_B DESC) FROM table GROUP BY col_A;

然而，这会输出:

| col_A | col_B   |
|-------|---------|
| 1     | {1,2,3} |
| 2     | {1,2,3} |
| 3     | {1,2}   |

Answer 1

您似乎想要聚合由 col_a 分组的 col_b，然后聚合由聚合数组分组的 col_a。您可以使用嵌套查询来执行此操作，您已经执行了嵌套查询的第一步:

SELECT array_agg(col_a), col_b
FROM (SELECT col_a, array_agg(DISTINCT col_b ORDER BY col_b) AS col_b
      FROM example GROUP BY col_a) grouped_b
GROUP BY col_b;

( online demo )