[英]How to group result by array column in Postgres?
I have such a table 我有这样一张桌子
id SERIAL,
user_id INT,
community_id INT[],
The table filled this way: 表格填写方式如下:
id | user_id | community_id
1 | 1 | {2, 4}
2 | 5 | {2, 5}
3 | 10 | {2, 4}
I'd like to get COUNT of users which each community has, community_id is array cuz user can be in several community at the same time. 我想获得每个社区拥有的COUNT个用户,community_id是数组cuz用户可以同时在多个社区中。
The query should be simple as: 查询应该简单如下:
SELECT community_id, COUNT(user_id) FROM tbl GROUP BY community_id
The result should be like this: 结果应该是这样的:
community_id | user_count
2 | 3
4 | 2
5 | 1
I do not know how to GROUP BY
array column. 我不知道如何GROUP BY
数组列。 Can anybody help me ? 有谁能够帮我 ?
You can use unnest()
to get a normalized view on the data, and the aggregate: 您可以使用unnest()
来获取数据的标准化视图和聚合:
select community_id, count(*)
from (
select unnest(community_id) as community_id
from tbl
) t
group by community_id
order by community_id;
But you should really fix your data model. 但是你应该真正修复你的数据模型。
select unnest(community_id) community_id
,count(user_id) user_count
from table_name
group by 1 --community_id = 1 and user_count = 2 (index of a column in select query)
order by 1 --
unnest(anyarray) : Expand an array to a set of rows unfst(anyarray) : 将数组扩展为一组行
ie select unnest(ARRAY[1,2])
will give 即select unnest(ARRAY[1,2])
将给出
unnest
------
1
2
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