我正在寻找聚合函数的 sql 模式来聚合数组。如果我有 2 行:
|id | array |
|----+---------------|
|1 | [1,2,3,4] |
|1 | [5,6] |
|1 | [7,8] |
|--------------------|
我想做以下事情:
select id, *aggregate_function*(array)
from table
group by id
我想要的结果是:
|id | *aggregate_function* |
|-----+-----------------------|
|1 | [1,2,3,4,5,6,7,8] |
|-----------------------------|
没有执行此聚合的本机 postgres 函数。但也许这里可以使用 sql 模式?
这样的事情应该有效:
with mytable as
(
select 1 as id, array[1, 2, 3, 4] as myarray
union all
select 1 as id, array[5, 6] as myarray
union all
select 1 as id, array[7, 8] as myarray
)
select
id,
array_agg(elements order by elements)
from mytable, unnest(myarray) as elements
group by id
这里有一些关于构建自定义函数的讨论:在分组/聚合期间连接/合并数组值
您可以取消嵌套然后分组:
WITH x (id, arr) AS (
VALUES
(1, ARRAY[1,2,3,4])
, (1, ARRAY[5,6])
, (1, ARRAY[7, 8])
)
SELECT id, ARRAY_AGG(splitup)
FROM (
SELECT
id
, unnest(arr) splitup
FROM x) splitup
GROUP BY 1
一个选项是创建自定义聚合:
CREATE FUNCTION array_union(a ANYARRAY, b ANYARRAY)
RETURNS ANYARRAY AS
$$
SELECT array_agg(x)
FROM (
SELECT unnest(a) x
UNION ALL
SELECT unnest(b)
) AS u
$$ LANGUAGE SQL;
CREATE AGGREGATE array_union_agg(ANYARRAY) (
SFUNC = array_union,
STYPE = ANYARRAY,
INITCOND = '{}'
);
然后您可以简单地使用:
WITH x(arr) AS (
VALUES
(ARRAY[1,2,3,4]),
(ARRAY[5,6]),
(ARRAY[7,8])
)
SELECT array_union_agg(arr)
FROM x;
查询结果为:
array_union_agg
-----------------
{1,2,3,4,5,6,7,8}
上面的版本做了数组concatenation.
使真正的union就像数组是集合一样,可以通过在
UNION ALL
函数的定义中用UNION
替换array_union
来实现。