Deleting a jsonb array item by name

user_492293 0
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I have the following table

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"] }');

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);

and update like this

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

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

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

Update

Delete by index

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

How can i delete by name?

jsonb postgresql
2 Answers

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;

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;

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).

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;

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

SELECT *
FROM country
WHERE (extra_info -> 'flag_colours') ? 'red'
user_112710480

Actually PG12 allows to do it without JOIN LATERAL:

SELECT jsonb_path_query_array(j #> '{flag_colours}', '$[*] ? (@ != "red")'),
       jsonb_set(j, '{flag_colours}', jsonb_path_query_array(j #> '{flag_colours}', '$[*] ? (@ != "red")'))
  FROM (SELECT '{ "name" : "France", "population" : "65000000",
                  "flag_colours": ["red", "blue","white"]}'::jsonb AS j
       ) AS j
 WHERE j @? '$.flag_colours[*] ? (@ == "red")';

 jsonb_path_query_array |                                    jsonb_set                                    
------------------------+---------------------------------------------------------------------------------
 ["blue", "white"]      | {"name": "France", "population": "65000000", "flag_colours": ["blue", "white"]}
(1 row)
user_59829620
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