Question

我有一张表格如下：

   id    | similar_id|
 --------+-----------+
    1    |     2     |
    1    |     3     |
    2    |     1     |
    2    |     3     |
    3    |     1     |
    3    |     2     |
    4    |     5     |
    5    |     4     |

如何编写优化的sql查询，以便找到类似的组？
即，组1 - > {1,2,3}，Group2 - ＆gt; {4,5}

。请参阅，我知道数据可以更好地组织。

Answer 1

select distinct (
    select array_agg(a order by a)
    from unnest(a) a(a)
) as "group"
from (
    select id || array_agg(similar_id) a
    from t
    group by id
) s
order by 1
;
  group  
---------
 {1,2,3}
 {4,5}

从这些数据：

create table t (id int, similar_id int);
insert into t (id, similar_id) values
(1,2),
(1,3),
(2,1),
(2,3),
(3,1),
(3,2),
(4,5),
(5,4);

Answer 2

简单的纯SQL：

SELECT DISTINCT groups
FROM (
  SELECT id, array_agg(similar_id) groups
  FROM (
    SELECT id, similar_id
    FROM grp
    UNION
    SELECT DISTINCT id, id
    FROM grp
    ORDER BY 1, 2) subsub
  GROUP BY 1) sub
ORDER BY 1;

这将产生：

 groups 
---------
 {1,2,3} 
 {4,5}

这里的诀窍是使用UNION，使每个id与自身和similar_id配对，然后它只是一个聚合问题。< / p>

如何从此数据集中创建组？

2 个答案: