arrays - 在处理空列值时连接数组列时保持一致的 PostgreSQL 数组列索引

Question

给定以下起始数据:

CREATE TABLE t1 AS
  SELECT generate_series(1, 20) AS id,
    (SELECT array_agg(generate_series) FROM generate_series(1, 6)) as array_1;

CREATE TABLE t2 AS
  SELECT generate_series(5, 10) AS id,
    (SELECT array_agg(generate_series) FROM generate_series(7, 10)) as array_2;

CREATE TABLE t3 AS
  SELECT generate_series(8, 15) AS id,
    (SELECT array_agg(generate_series) FROM generate_series(11, 15)) as array_3;

我想在几个表之间进行外部连接，每个表都有一个固定长度的数组列，该列在给定表中是统一的，但可能因表而异(如上例所示)，连接数组列在每个表中放入一个大数组列。我想知道是否有一种有效或直接的方法可以在新的组合列中保持一致的索引，将 NULL 列值(由外部连接引起)替换为 NULL 值，以便最终的数组列具有统一的长度。与上面的示例不同，在我的实际用例中，我不会知道每个表的数组列的长度先验，只是它在整个表中具有统一的长度。换句话说，而不是这个查询:

SELECT id, (array_1 || array_2 || array_3 ) AS combined_array FROM
t1 LEFT OUTER JOIN t2 USING(id) LEFT OUTER JOIN t3 USING (id);

产生:

id |            combined_array
----+---------------------------------------
 1 | {1,2,3,4,5,6}
 2 | {1,2,3,4,5,6}
 3 | {1,2,3,4,5,6}
 4 | {1,2,3,4,5,6}
 5 | {1,2,3,4,5,6,7,8,9,10}
 6 | {1,2,3,4,5,6,7,8,9,10}
 7 | {1,2,3,4,5,6,7,8,9,10}
 8 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
 9 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
10 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
11 | {1,2,3,4,5,6,11,12,13,14,15}
12 | {1,2,3,4,5,6,11,12,13,14,15}
13 | {1,2,3,4,5,6,11,12,13,14,15}
14 | {1,2,3,4,5,6,11,12,13,14,15}
15 | {1,2,3,4,5,6,11,12,13,14,15}
16 | {1,2,3,4,5,6}
17 | {1,2,3,4,5,6}
18 | {1,2,3,4,5,6}
19 | {1,2,3,4,5,6}
20 | {1,2,3,4,5,6}
(20 rows)

我希望结果看起来像:

id |            combined_array
----+---------------------------------------
 1 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
 2 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
 3 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
 4 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
 5 | {1,2,3,4,5,6,7,8,9,10,NULL,NULL,NULL,NULL,NULL}
 6 | {1,2,3,4,5,6,7,8,9,10,NULL,NULL,NULL,NULL,NULL}
 7 | {1,2,3,4,5,6,7,8,9,10,NULL,NULL,NULL,NULL,NULL}
 8 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
 9 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
10 | {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
11 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,11,12,13,14,15}
12 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,11,12,13,14,15}
13 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,11,12,13,14,15}
14 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,11,12,13,14,15}
15 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,11,12,13,14,15}
16 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
17 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
18 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
19 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
20 | {1,2,3,4,5,6,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}
(20 rows)

这样每一行都包含一个长度为 15 的数组。

Answer 1

为了回答我自己的问题，这是我提出的似乎可以完成这项工作的查询。它对我来说似乎不是特别优雅或高效，所以肯定仍然对其他答案持开放态度。

SELECT id, (
  coalesce(array_1, array_fill(NULL::INT,
    ARRAY[(SELECT max(array_length(array_1, 1)) FROM t1)])) ||
  coalesce(array_2, array_fill(NULL::INT,
    ARRAY[(SELECT max(array_length(array_2, 1)) FROM t2)])) ||
  coalesce(array_3, array_fill(NULL::INT,
    ARRAY[(SELECT max(array_length(array_3, 1)) FROM t3)]))
) AS combined_array FROM
t1 LEFT OUTER JOIN t2 USING(id) LEFT OUTER JOIN t3 USING (id);