Merging Concatenating JSON(B) columns in query

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?

---

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

EDIT : for PostgreSQL 9.5+, look at Zubin's answer below

---

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;

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.

---

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

链接地址: http://www.djcxy.com/p/37830.html

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