sql - 如何在 SQL 中查询表的层次结构

Question

我有一张 table ，开会。在这些 session 中存在一个层次结构。其中一些是年度 session ，大多数只是定期 session 。

所有常规 session 将与至少一个连接表meeting_yearly_meeting 相关联。 meeting_yearly_meeting 有两列:meeting_id 和 yearly_meeting_id。

下面是这两个表的样子:

session :

id SERIAL PRIMARY KEY,
title VARCHAR(255),
mappable BOOLEAN,
phone VARCHAR(255),
email VARCHAR(255),
city VARCHAR(255),
address VARCHAR(255),
zip VARCHAR(255),
latitude NUMERIC,
longitude NUMERIC,
description VARCHAR(255),
worship_time TIME,
state VARCHAR(255),
website VARCHAR(255),
lgbt_affirming BOOLEAN,
created TIMESTAMP default current_timestamp,
updated TIMESTAMP default current_timestamp

meeting_yearly_meeting:

id SERIAL PRIMARY KEY,
meeting_id SMALLINT,
yearly_meeting_id SMALLINT,
created TIMESTAMP default current_timestamp,
updated TIMESTAMP default current_timestamp

因此，从我的 /meetings 端点，我想返回所有 session 的集合——定期 session 和年度 session 。我想返回 session 及其所有专栏，以及一个额外的专栏:yearly_meeting。

对于具有一个或多个关联的meeting_yearly_meeting 记录的meeting 记录，yearly_meeting 将是标题的逗号分隔列表 的 meeting 记录被指定为该 meeting 的年度 session 。对于那些没有任何关联的 meeting_yearly_meeting 记录的 session (因此它们本身就是年度 session )，我希望 yearly_meeting 字段为 NULL。

在我追求这个目标的过程中，我尝试了这样的事情:

SELECT t1.*, t2.meeting_yearly_meeting AS yearly_meeting
FROM (
  SELECT * FROM meeting
  FULL JOIN meeting_yearly_meeting ON meeting.id = meeting_yearly_meeting.yearly_meeting_id;
) as t1, 
(
  SELECT CASE WHEN (meeting_yearly_meeting.id IS NOT NULL)
    THEN (SELECT title FROM meeting WHERE meeting.id = meeting_yearly_meeting.yearly_meeting_id)
    ELSE NULL
    END
  FROM (
    SELECT meeting_yearly_meeting.* FROM meeting
    FULL JOIN meeting_yearly_meeting ON meeting.id = meeting_yearly_meeting.meeting_id
  ) as meeting_yearly_meeting;
) as t2;

但这会引发语法错误。

我很欣赏其他人可能有的任何见解。如果您需要任何其他背景信息或说明，请告诉我!

更新:

示例 session 数据:https://gist.github.com/micahbales/4013399c3fd23a0caf108124dab827c8

示例 meeting_yearly_meeting 数据:https://gist.github.com/micahbales/fcbdeef282bd7bf1014606cee43bfb5e

预期返回值示例:https://gist.github.com/micahbales/13d2aafdc5d43c4b948dc39c2df51569

Answer 1

您可以尝试离开加入年度 session ，然后使用 string_agg() 获取您的逗号分隔列表。

SELECT m1.id,
       m1.title,
       m1.mappable,
       m1.phone,
       m1.email,
       m1.city,
       m1.address,
       m1.zip,
       m1.latitude,
       m1.longitude,
       m1.description,
       m1.worship_time,
       m1.state,
       m1.website,
       m1.lgbt_affirming,
       m1.created,
       m1.updated,
       string_agg(m2.title, ', ') yearly_meeting
       FROM meeting m1
            LEFT JOIN meeting_yearly_meeting mym1
                      ON mym1.meeting_id = m1.id
            LEFT JOIN meeting m2
                      ON m2.id = mym1.yearly_meeting_id
       GROUP BY m1.id,
                m1.title,
                m1.mappable,
                m1.phone,
                m1.email,
                m1.city,
                m1.address,
                m1.zip,
                m1.latitude,
                m1.longitude,
                m1.description,
                m1.worship_time,
                m1.state,
                m1.website,
                m1.lgbt_affirming,
                m1.created,
                m1.updated;

---

编辑:

更“紧凑”的解决方案可能是使用相关子查询。

SELECT m1.*,
       (SELECT string_agg(m2.title, ', ')
               FROM meeting_yearly_meeting mym1
                    LEFT JOIN meeting m2
                              ON m2.id = mym1.yearly_meeting_id
               WHERE mym1.meeting_id = m1.id) yearly_meeting
       FROM meeting m1;

但请注意，虽然它的代码更少，但不一定更快。