Deleting a jsonb array item by name - postgresql

Question

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?

Answer 1

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'

Answer 2

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)