将集合返回函数 (json_array_elements) 的结果与 table 列联接

Question

假设我有两个表：

User_Combination

+--------+----------------+
|   id   |   combination  |
+--------+----------------+
|    6   |     [1, 2]     |
|    9   |     [2, 3]     |
+--------+----------------+

颜色

+--------+----------------+
|   id   |   color        |
+--------+----------------+
|    1   |       Blue     |
|    2   |       Yellow   |
|    3   |       Green    |
+--------+----------------+

我正在尝试将 json_array_elements(color) 的结果与 Elements 的 id 相结合。例如

的结果

select json_array_elements(color) as CombinationID
from User_Combination where id = 6;

是

+-------------------+
|   CombinationID   |
+-------------------+
|    1              |
|    2              |
+-------------------+

我无法加入 CombinationID 和 Colors.id。当我尝试 SQL 命令时，例如：

select json_array_elements(article_data) AS articlesInOutfits (color) as CombinationID
from User_Combination uc JOIN Colors co ON co.id = articlesInOutfits;

或

select json_array_elements(article_data) AS articlesInOutfits (color) as CombinationID
from User_Combination uc JOIN Colors co ON co.id = uc.articlesInOutfits;

它说 articlesInOutfits 不存在。
有什么建议吗？

Answer 1

使用unnest()得到解压组合：

select id, unnest(combination) cid
from user_combination;

 id | cid 
----+-----
  6 |   1
  6 |   2
  9 |   2
  9 |   3
(4 rows)

使用unpacked cids加入colors:

select u.id, color
from (
    select id, unnest(combination) cid
    from user_combination
    ) u
join colors c
on cid = c.id;

 id | color  
----+--------
  6 | Blue
  6 | Yellow
  9 | Yellow
  9 | Green
(4 rows)

使用聚合函数（例如 json_agg()）为用户聚合合并的颜色：

select u.id, json_agg(color)
from (
    select id, unnest(combination) cid
    from user_combination
    ) u
join colors c
on cid = c.id
group by 1;

 id |      json_agg       
----+---------------------
  9 | ["Yellow", "Green"]
  6 | ["Blue", "Yellow"]
(2 rows)

如果 combination 是类型 json 你应该在横向连接中使用 json_array_elements():

select u.id, json_agg(color)
from (
    select id, cid
    from user_combination,
    lateral json_array_elements(combination) cid
    ) u 
join colors c
on cid::text::int = c.id
group by 1;

将集合返回函数 (json_array_elements) 的结果与 table 列联接

Join result of set-returning function (json_array_elements) with table column

sql

json

postgresql

set-returning-functions