Question

我的表跟随包含int数组中的user_id和follower_ids：

id | user_id | follower_ids
---|---------|-------------
1  | 1       | {2,3,4}
2  | 2       | {1}
3  | 3       | {1,2}
4  | 4       | {1}

我想得到像这样的结果

user_id | count
--------| -----
1       | 3
2       | 2
3       | 1
4       | 1

如何运行查询？

谢谢。

Answer 1

您可以使用array_length()功能

select user_id
      ,array_length(follower_ids,1) count
from bar

Answer 2

WITH t(id,user_id,follower_ids) AS ( VALUES
  (1,1,ARRAY[2,3,4]),
  (2,2,ARRAY[1]),
  (3,3,ARRAY[1,2]),
  (3,4,ARRAY[1])
)
SELECT
  follower AS user_id,
  count(follower) AS follower_count
FROM t,unnest(t.follower_ids) AS follower
GROUP BY 1
ORDER BY 1;

输出：

 user_id | follower_count 
---------+----------------
       1 |              3
       2 |              2
       3 |              1
       4 |              1
(4 rows)

如何计算数组postgres上的每一行

2 个答案: