Merging Concatenating JSON(B) columns in query - postgresql

Question

Using Postgres 9.4, I am looking for a way to merge two (or more) json or jsonb columns in a query. Consider the following table as an example:
id | json1 | json2
----------------------------------------
1 | {'a':'b'} | {'c':'d'}
2 | {'a1':'b2'} | {'f':{'g' : 'h'}}
Is it possible to have the query return the following:
id | json
----------------------------------------
1 | {'a':'b', 'c':'d'}
2 | {'a1':'b2', 'f':{'g' : 'h'}}
Unfortunately, I can't define a function as described here. Is this possible with a "traditional" query?

Answer 1

In Postgres 9.5+ you can merge JSONB like this:
select json1 || json2;
Or, if it's JSON, coerce to JSONB if necessary:
select json1::jsonb || json2::jsonb;
Or:
select COALESCE(json1::jsonb||json2::jsonb, json1::jsonb, json2::jsonb);
(Otherwise, any null value in json1 or json2 returns an empty row)
For example:
select data || '{"foo":"bar"}'::jsonb from photos limit 1;
?column?
----------------------------------------------------------------------
{"foo": "bar", "preview_url": "https://unsplash.it/500/720/123"}
Kudos to #MattZukowski for pointing this out in a comment.

Answer 2

Here is the complete list of build-in functions that can be used to create json objects in PostgreSQL. http://www.postgresql.org/docs/9.4/static/functions-json.html
row_to_json and json_object doest not allow you to define your own keys, so it can't be used here
json_build_object expect you to know by advance how many keys and values our object will have, that's the case in your example, but should not be the case in the real world
json_object looks like a good tool to tackle this problem but it forces us to cast our values to text so we can't use this one either
Well... ok, wo we can't use any classic functions.
Let's take a look at some aggregate functions and hope for the best... http://www.postgresql.org/docs/9.4/static/functions-aggregate.html
json_object_agg Is the only aggregate function that build objects, that's our only chance to tackle this problem. The trick here is to find the correct way to feed the json_object_agg function.
Here is my test table and data
CREATE TABLE test (
id SERIAL PRIMARY KEY,
json1 JSONB,
json2 JSONB
);
INSERT INTO test (json1, json2) VALUES
('{"a":"b", "c":"d"}', '{"e":"f"}'),
('{"a1":"b2"}', '{"f":{"g" : "h"}}');
And after some trials and errors with json_object here is a query you can use to merge json1 and json2 in PostgreSQL 9.4
WITH all_json_key_value AS (
SELECT id, t1.key, t1.value FROM test, jsonb_each(json1) as t1
UNION
SELECT id, t1.key, t1.value FROM test, jsonb_each(json2) as t1
)
SELECT id, json_object_agg(key, value)
FROM all_json_key_value
GROUP BY id
For PostgreSQL 9.5+, look at Zubin's answer.

Answer 3

This function would merge nested json objects
create or replace function jsonb_merge(CurrentData jsonb,newData jsonb)
returns jsonb
language sql
immutable
as $jsonb_merge_func$
select case jsonb_typeof(CurrentData)
when 'object' then case jsonb_typeof(newData)
when 'object' then (
select jsonb_object_agg(k, case
when e2.v is null then e1.v
when e1.v is null then e2.v
when e1.v = e2.v then e1.v
else jsonb_merge(e1.v, e2.v)
end)
from jsonb_each(CurrentData) e1(k, v)
full join jsonb_each(newData) e2(k, v) using (k)
)
else newData
end
when 'array' then CurrentData || newData
else newData
end
$jsonb_merge_func$;

Answer 4

Looks like nobody proposed this kind of solution yet, so here's my take, using custom aggregate functions:
create or replace aggregate jsonb_merge_agg(jsonb)
(
sfunc = jsonb_concat,
stype = jsonb,
initcond = '{}'
);
create or replace function jsonb_concat(a jsonb, b jsonb) returns jsonb
as 'select $1 || $2'
language sql
immutable
parallel safe
;
Note: this is using || which replaces existing values at same path instead of deeply merging them.
Now jsonb_merge_agg is accessible like so:
select jsonb_merge_agg(some_col) from some_table group by something;

Answer 5

Also you can tranform json into text, concatenate, replace and convert back to json. Using the same data from Clément you can do:
SELECT replace(
(json1::text || json2::text),
'}{',
', ')::json
FROM test
You could also concatenate all json1 into single json with:
SELECT regexp_replace(
array_agg((json1))::text,
'}"(,)"{|\\| |^{"|"}$',
'\1',
'g'
)::json
FROM test
This is a very old solution, since 9.4 you should use json_object_agg and simple || concatenate operator. Keeping here just for reference.

Answer 6

However this question is answered already some time ago; the fact that when json1 and json2 contain the same key; the key appears twice in the document, does not seem to be best practice.
Therefore u can use this jsonb_merge function with PostgreSQL 9.5:
CREATE OR REPLACE FUNCTION jsonb_merge(jsonb1 JSONB, jsonb2 JSONB)
RETURNS JSONB AS $$
DECLARE
result JSONB;
v RECORD;
BEGIN
result = (
SELECT json_object_agg(KEY,value)
FROM
(SELECT jsonb_object_keys(jsonb1) AS KEY,
1::int AS jsb,
jsonb1 -> jsonb_object_keys(jsonb1) AS value
UNION SELECT jsonb_object_keys(jsonb2) AS KEY,
2::int AS jsb,
jsonb2 -> jsonb_object_keys(jsonb2) AS value ) AS t1
);
RETURN result;
END;
$$ LANGUAGE plpgsql;
The following query returns the concatenated jsonb columns, where the keys in json2 are dominant over the keys in json1:
select id, jsonb_merge(json1, json2) from test

Answer 7

FYI, if someone's using jsonb in >= 9.5 and they only care about top-level elements being merged without duplicate keys, then it's as easy as using the || operator:
select '{"a1": "b2"}'::jsonb || '{"f":{"g" : "h"}}'::jsonb;
?column?
-----------------------------
{"a1": "b2", "f": {"g": "h"}}
(1 row)

Answer 8

Try this, if anyone having an issue for merging two JSON object
select table.attributes::jsonb || json_build_object('foo',1,'bar',2)::jsonb FROM table where table.x='y';

Answer 9

CREATE OR REPLACE FUNCTION jsonb_merge(pCurrentData jsonb, pMergeData jsonb, pExcludeKeys text[])
RETURNS jsonb IMMUTABLE LANGUAGE sql
AS $$
SELECT json_object_agg(key,value)::jsonb
FROM (
WITH to_merge AS (
SELECT * FROM jsonb_each(pMergeData)
)
SELECT *
FROM jsonb_each(pCurrentData)
WHERE key NOT IN (SELECT key FROM to_merge)
AND ( pExcludeKeys ISNULL OR key <> ALL(pExcludeKeys))
UNION ALL
SELECT * FROM to_merge
) t;
$$;
SELECT jsonb_merge('{"a": 1, "b": 9, "c": 3, "e":5}'::jsonb, '{"b": 2, "d": 4}'::jsonb, '{"c","e"}'::text[]) as jsonb

Answer 10

works well as an alternative to || when recursive deep merge is required (found here) :
create or replace function jsonb_merge_recurse(orig jsonb, delta jsonb)
returns jsonb language sql as $$
select
jsonb_object_agg(
coalesce(keyOrig, keyDelta),
case
when valOrig isnull then valDelta
when valDelta isnull then valOrig
when (jsonb_typeof(valOrig) <> 'object' or jsonb_typeof(valDelta) <> 'object') then valDelta
else jsonb_merge_recurse(valOrig, valDelta)
end
)
from jsonb_each(orig) e1(keyOrig, valOrig)
full join jsonb_each(delta) e2(keyDelta, valDelta) on keyOrig = keyDelta
$$;