在 Postgres 11.7 中将 ORDINALITY 添加到扩展的 JSON 数组

Posted 2023-04-12

【中文标题】在 Postgres 11.7 中将 ORDINALITY 添加到扩展的 JSON 数组

【英文标题】：Add ORDINALITY to expanded JSON array in Postgres 11.7

【发布时间】：2020-05-10 04:21:08

【问题描述】：

我正在获取两个 JSONB 数组，将它们解包并组合结果。我正在尝试将 WITH ORDINALITY 添加到 JSON 数组解包中。我一直无法弄清楚如何添加WITH ORDINALITY。出于某种原因，我在 Postgres 11 的 JSON 工具的文档中找不到 WITH ORDINALITY：

https://www.postgresql.org/docs/11/functions-json.html

我见过使用jsonb_array_elements....WITH ORDINALITY 的示例，但无法让它工作。一、基于Postgres数组的函数式示例：

WITH
first AS (
SELECT * FROM
    UNNEST (ARRAY['Charles','Jane','George','Percy']) WITH ORDINALITY AS x(name_, index)
),

last AS (
SELECT * FROM
    UNNEST (ARRAY['Dickens','Austen','Eliot']) WITH ORDINALITY AS y(name_, index)
)

SELECT first.name_ AS first_name,
       last.name_  AS last_name

  FROM first
  JOIN last ON (last.index = first.index)

这给出了所需的输出：

first_name  last_name
Charles     Dickens
Jane        Austen
George      Eliot

我正在使用ORDINALITY 索引来创建JOIN，因为我正在组合两个列表以进行成对比较。我可以假设我的列表大小相同。

但是，我的输入将是 JSON 数组，而不是 Postgres 数组。我已经使用jsonb_to_recordset 进行了拆包工作，但还没有让序数生成工作。这是一个正确完成拆包部分的示例：

DROP FUNCTION IF EXISTS tools.try_ordinality (jsonb, jsonb);
CREATE OR REPLACE FUNCTION tools.try_ordinality (
     base_jsonb_in         jsonb,
     comparison_jsonb_in   jsonb)

RETURNS TABLE (
    base_text         citext,
    base_id           citext,
    comparison_text   citext,
    comparison_id     citext)

AS $BODY$

BEGIN

RETURN QUERY

WITH
base_expanded AS (

 select *
   from jsonb_to_recordset (
          base_jsonb_in) 
      AS base_unpacked (text citext, id citext)
 ),

comparison_expanded AS (

 select *
   from jsonb_to_recordset (
          comparison_jsonb_in)
      AS comparison_unpacked (text citext, id citext)
 ),

combined_lists AS (
select base_expanded.text       AS base_text,
       base_expanded.id         AS base_id,
       comparison_expanded.text AS comparison_text,
       comparison_expanded.id   AS comparison_id

  from base_expanded,
       comparison_expanded
)

select * 

   from combined_lists;

END
$BODY$
LANGUAGE plpgsql;

select *  from try_ordinality (
'[
    "text":"Fuzzy Green Bunny","id":"1",
    "text":"Small Gray Turtle","id":"2"
    ]',

'[
    "text":"Red Large Special","id":"3",
    "text":"Blue Small","id":"4",
    "text":"Green Medium Special","id":"5"
  ]'
);

但那是CROSS JOIN

base_text    base_id    comparison_text    comparison_id
Fuzzy Green Bunny    1    Red Large Special      3
Fuzzy Green Bunny    1    Blue Small             4
Fuzzy Green Bunny    1    Green Medium Special   5
Small Gray Turtle    2    Red Large Special      3
Small Gray Turtle    2    Blue Small             4
Small Gray Turtle    2    Green Medium Special   5

我追求的是只有两行的成对结果：

Fuzzy Green Bunny    1    Red Large Special    3
Small Gray Turtle    2    Blue Small           4

我已经尝试切换到jsonb_array_elements，就像在这个 sn-p 中一样：

WITH
base_expanded AS (

 select *
   from jsonb_array_elements (
          base_jsonb_in) 
      AS base_unpacked (text citext, id citext)
 ),

我回来了

ERROR:  a column definition list is only allowed for functions returning "record"

有没有一种直接的方法来获取解压缩的 JSON 数组的序数？在 Postgres 数组上使用 UNNEST 非常简单。

我很高兴得知我搞砸了语法。

如果有帮助，我可以CREATE TYPE。

如果操作简单，我可以转换为 Postgres 数组。

感谢您的任何建议。

【问题讨论】：

WITH ORDINALITY 适用于任何集合返回函数。 JSON 确实具有您可以使用的集合返回函数，但在那里记录它会很奇怪，因为它在那里的操作方式与非 JSON 集合返回函数的操作方式相同。

【参考方案1】：

你做的完全一样。

with first as (
  select *
  from jsonb_array_elements('[
    "text":"Fuzzy Green Bunny","id":"1",
    "text":"Small Gray Turtle","id":"2"
    ]'::jsonb) with ordinality as f(element, idx)
), last as (
  select *
  from jsonb_array_elements('[
    "text":"Red Large Special","id":"3",
    "text":"Blue Small","id":"4",
    "text":"Green Medium Special","id":"5"
  ]'::jsonb) with ordinality as f(element, idx)
)
SELECT first.element ->> 'text' AS first_name,
       last.element ->> 'text' AS last_name
FROM first
  JOIN last ON last.idx = first.idx