sql - 带有数组索引(键)的 PostgreSQL json_array_elements

Question

简单的查询工作正常:

SELECT json_array_elements_text('["first", "third", "second"]'::json)

但我也想以某种方式检索数组键，所以输出如下:

key    value
 0     first
 1     third
 2     second

UPD

好像 row_number() 是一个 p̶r̶o̶p̶e̶r̶ 解决方案，但我不知道如何进一步使用它。

假设我有“帖子”表，每个帖子都包含一组 JSON 格式的相关评论:

SELECT id, title, comments FROM posts

id     title             comments
 1    Title 1  ["comment 1", "comment 2"]
 2    Title 2  ["comment 3", "comment 4", "comment 5"]
 3    Title 3  ["comment 6"]

目标不仅是扩展评论值，还有键:

Tricky SQL here

id     title    comment   key
 1    Title 1  comment 1   0
 1    Title 1  comment 2   1
 2    Title 2  comment 3   0
 2    Title 2  comment 4   1
 2    Title 2  comment 5   2
 3    Title 3  comment 6   0

UPD2

使用 row_numbers() 的解决方案:

SELECT *, row_number() OVER (PARTITION BY id) - 1 AS key
FROM (
  SELECT id, title, json_array_elements_text(comments::json) AS comment
  FROM posts
) p

提前致谢!

Answer 1

使用函数json_array_elements_text()有序数:

with my_table(id, title, comments) as (
values
(1, 'Title 1', '["comment 1", "comment 2"]'::json),
(2, 'Title 2', '["comment 3", "comment 4", "comment 5"]'),
(3, 'Title 3', '["comment 6"]')
)

select id, title, value as comment, ordinality- 1 as key
from my_table
cross join json_array_elements_text(comments) with ordinality

 id |  title  |  comment  | key 
----+---------+-----------+-----
  1 | Title 1 | comment 1 |   0
  1 | Title 1 | comment 2 |   1
  2 | Title 2 | comment 3 |   0
  2 | Title 2 | comment 4 |   1
  2 | Title 2 | comment 5 |   2
  3 | Title 3 | comment 6 |   0
(6 rows)

来自 the documentation:

If the WITH ORDINALITY clause is specified, an additional column of type bigint will be added to the function result columns. This column numbers the rows of the function result set, starting from 1.