按名称删除jsonb数组项 [英] Deleting a jsonb array item by name

问题描述

我有下表

CREATE TABLE country (
    id      INTEGER NOT NULL PRIMARY KEY ,
    name        VARCHAR(50),
    extra_info  JSONB
);
 
INSERT INTO country(id,extra_info)
VALUES (1, '{ "name" : "France", "population" : "65000000", "flag_colours": ["red", "blue","white"]}');
 
INSERT INTO country(id,extra_info)
VALUES (2, '{ "name": "Spain", "population" : "47000000", "borders": ["Portugal", "France"] }');

我可以像这样向数组添加一个元素

and i can add an element to the array like this

UPDATE country SET extra_info = jsonb_set(extra_info, '{flag_colours,999999999}', '"green"', true);

并像这样更新

UPDATE country SET extra_info = jsonb_set(extra_info, '{flag_colours,0}', '"yellow"');

我现在想删除具有已知索引或名称的数组项.

I now would like to delete an array item with a known index or name.

我如何按索引或名称删除flag_color元素?

How would i delete a flag_color element by index or by name?

更新

按索引删除

UPDATE country SET extra_info = extra_info #- '{flag_colours,-1}'

如何删除姓名?

推荐答案

由于数组不能以直接的方式直接访问项目，因此我们可以尝试通过嵌套->来以不同的方式进行处理.过滤元素->把东西缝在一起.我已经编写了一个代码示例，其中包含有序注释，以提供帮助.

As Arrays do not have direct access to items in a straightforward way, we can try to approach this differently through unnesting -> filtering elements -> stitching things back together. I have formulated a code example with ordered comments to help.

CREATE TABLE new_country AS
-- 4. Return a new array (for immutability) that contains the new desired set of colors
SELECT id, name, jsonb_set(extra_info, '{flag_colours}', new_colors, FALSE)
FROM country
       -- 3. Use Lateral join to apply this to every row
       LEFT JOIN LATERAL (
  -- 1. First unnest the desired elements from the Json array as text (to enable filtering)
  WITH prep AS (SELECT jsonb_array_elements_text(extra_info -> 'flag_colours') colors FROM country)
  SELECT jsonb_agg(colors) new_colors -- 2. Form a new jsonb array after filtering
  FROM prep
  WHERE colors <> 'red') lat ON TRUE;

如果您只想更新受影响的列而不重新创建主表，则可以:

In the case you would like to update only the affected column without recreating the main table, you can:

UPDATE country
SET extra_info=new_extra_info
FROM new_country
WHERE country.id = new_country.id;

我将其细分为两个查询以提高可读性；但是，您也可以使用子查询代替创建新表(new_country).

I have broken it down to two queries to improve readability; however you can also use a subquery instead of creating a new table (new_country).

使用子查询，它应该看起来像:

With the subquery, it should look like:

UPDATE country
SET extra_info=new_extra_info
FROM (SELECT id, name, jsonb_set(extra_info, '{flag_colours}', new_colors, FALSE) new_extra_info
      FROM country
             -- 3. Use Lateral join to scale this across tables
             LEFT JOIN LATERAL (
        -- 1. First unnest the desired elements from the Json array as text (to enable filtering)
        WITH prep AS (SELECT jsonb_array_elements_text(extra_info -> 'flag_colours') colors FROM country)
        SELECT jsonb_agg(colors) new_colors -- 2. Form a new jsonb array after filtering
        FROM prep
        WHERE colors <> 'red') lat ON TRUE) new_country
WHERE country.id = new_country.id;

此外，您可以通过(自PostgreSQL 9.4起)过滤行:

Additionally, you may filter rows via (As of PostgreSQL 9.4):

SELECT *
FROM country
WHERE (extra_info -> 'flag_colours') ? 'red'

这篇关于按名称删除jsonb数组项的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！