PostgreSQL：聚合列表中的名称组合

Question

我有一个看起来像这样的数据库结构：

               Table "public.person"
 Column |  Type   | Collation | Nullable | Default 
--------+---------+-----------+----------+---------
 id     | integer |           | not null | 

                 Table "public.person_name"
 Column |       Type        | Collation | Nullable | Default 
--------+-------------------+-----------+----------+---------
 person | integer           |           | not null | 
 name   | character varying |           |          | 
Foreign-key constraints:
    "person_name_person_fkey" FOREIGN KEY (person) REFERENCES person(id)

                    Table "public.event"
 Column |       Type        | Collation | Nullable | Default 
--------+-------------------+-----------+----------+---------
 id     | integer           |           | not null | 
 name   | character varying |           |          | 

              Table "public.attendee"
 Column |  Type   | Collation | Nullable | Default 
--------+---------+-----------+----------+---------
 event  | integer |           |          | 
 person | integer |           |          | 
Foreign-key constraints:
    "attendee_event_fkey" FOREIGN KEY (event) REFERENCES public.event(id)
    "attendee_person_fkey" FOREIGN KEY (person) REFERENCES person(id)

一些示例数据：

person:
 id 
----
  0
  1
  2
  3

person_name:
 person |   name    
--------+-----------
      0 | Alex
      0 | Alexander
      1 | Barbara
      1 | Barb
      2 | Cecilia
      3 | Dave
      3 | David

event:
 id |    name    
----+------------
  0 | Wedding
  1 | Party
  2 | Funeral

attendee:
 event | person 
-------+--------
     0 |      0
     0 |      1
     0 |      2
     1 |      1
     1 |      2
     2 |      2
     2 |      3

我想做一个 select 声明，即 return 所有事件，所有与会者都有的昵称的每种组合都有一行，如下所示：

 event_id | event_name | attendee_list
----------+------------+---------------
        0 | Wedding    | Alex, Barbara, Cecilia
        0 | Wedding    | Alexander, Barbara, Cecilia
        0 | Wedding    | Alex, Barb, Cecilia
        0 | Wedding    | Alexander, Barb, Cecilia
        1 | Party      | Barbara, Cecilia
        1 | Party      | Barb, Cecilia
        2 | Funeral    | Cecilia, Dave
        2 | Funeral    | Cecilia, David

我最初的直觉是将所有表格连接在一起，按事件分组，然后使用 string_agg，但这会将每个人的昵称都放在列表中（当然，因为它是对整个加入）。我的第二次尝试是 select 来自子查询的与会者姓名，但子查询不能 return 多行。我也尝试过使用数组进行聚合，如 here, but you can't aggregate arrays of differing dimensionality. Finally, I tried using some recursive magic as described 所述，但发现很难适应我的问题，最终无法让它工作。

Answer 1

我想我已经通过之前链接的“递归魔法”弄明白了。问题是我的真实数据有点复杂，每个与会者在列表中都有一个“位置”，这并不总是适用于 r.id < t.id 约束。这是一个与问题中的示例数据一起使用的查询：

with recursive recur as (
    select
        array[person_name.person] as persons,
        array[name] as names,
        attendee.event
    from person_name
    join attendee
    on person_name.person=attendee.person
union all
    select
        persons || t.person,
        names || t.name,
        attendee.event
    from person_name t
    join recur r
    on t.person != all(r.persons)
    join attendee
    on t.person=attendee.person
    and attendee.event=r.event
)
select event, names
from recur
where cardinality(names)=(
    select count(*)
    from attendee
    where attendee.event=recur.event
);

这也会 return 为每个可能的订单与会者增加一行，但我对此很好（就像我说的，我的真实数据有一个限制它的“位置”字段）。如果您只需要一个排序，则必须在某处的数据中指定排序，因此例如添加 r.id < t.id 位就可以了。

Answer 2

这是执行此操作的递归查询。我做了一个人 ID 数组，在递归的每个阶段，我用 person_name table.

加入了下一个 ID

WITH RECURSIVE recur AS (
    SELECT 
        event as event_id, 
        event.name as event_name, 
        array_agg(person) as person_id_list, 
        ARRAY[]::text[] as person_name_list,
        1 as index
    FROM attendee, event 
    WHERE attendee.event = event.id 
    GROUP BY event, event.name
UNION ALL
    SELECT 
        event_id, 
        event_name, 
        person_id_list,
        person_name_list || person_name.name,
        index + 1
    FROM recur
    JOIN person_name on (person_name.person = recur.person_id_list[recur.index])
    WHERE cardinality(recur.person_id_list) >= recur.index
)
SELECT event_id, event_name, array_to_string(person_name_list, ', ') as attendee_list
FROM recur
WHERE cardinality(recur.person_id_list) < recur.index
ORDER BY event_id;

PostgreSQL：聚合列表中的名称组合

PostgreSQL: Aggregating combinations of names in list

sql

database

postgresql

join

aggregate-functions