PostgreSQL - GROUP_CONCAT for JSONB column - postgresql

Question

I try to find a way to concat JSONB values using Postgres.
For example I have two lines :
INSERT INTO "testConcat" ("id", "json_data", "groupID")
VALUES (1, {"name": "JSON_name1", "value" : "Toto"}, 5);
INSERT INTO "testConcat" ("id", "json_data", "groupID")
VALUES (2, {"name": "JSON_name2"}, 5);
I would like to do something like :
SELECT GROUP_CONCAT(json_data)
FROM testConcat
GROUP BY groupID
AND as results to obtain something like :
[{"name": "JSON_name1", "value": "Toto"}, {"name": "JSON_name2"}]
I try the creation of aggregate function, but when there is the same key into the JSON, then they are merged and only the last values is preserved :
DROP AGGREGATE IF EXISTS jsonb_merge(jsonb);
CREATE AGGREGATE jsonb_merge(jsonb) (
SFUNC = jsonb_concat(jsonb, jsonb),
STYPE = jsonb,
INITCOND = '{}'
);
When I use this function as here :
SELECT jsonb_merge(json_data)
FROM testConcat
GROUP BY groupID
The result is :
{"name": "JSON_name2", "value": "Toto"}
And not as those that I want because the
{"name": "JSON_name1"}
is missing. The function preserve only the different keys and merge the other one with the last value.
Thanks for any help

Answer 1

If there is always only a single key/value pair in the JSON document, you can do this without a custom aggregate function:
SELECT groupid, jsonb_object_agg(k,v order by id)
FROM testconcat, jsonb_each(json_data) as x(k,v)
group by groupid;
The "last" value is defined by the ordering on the id column
The custom aggregate function might be faster though.

Answer 2

Finally I just find a solution, even if it is not the best, it seems to works.
I create the agreate function, as previously described with a small modification :
DROP AGGREGATE IF EXISTS jsonb_merge(jsonb);
CREATE AGGREGATE jsonb_merge(jsonb) (
SFUNC = jsonb_concat(jsonb, jsonb),
STYPE = jsonb,
INITCOND = '[]'
);
I just replace :
INITCOND = '{}'
with
INITCOND = '[]'
And after used it as previously :
SELECT jsonb_merge(json_data)
FROM testConcat
GROUP BY groupID