PostgreSQL update JSONB column with value from another column - sql

Question

I want to migrate data from one column (varchar) to another column (jsonb)
Column | Type | Modifiers
------------+-----------------------------+--------------------------------------------------------
id | integer | not null default nextval('merchants_id_seq'::regclass)
name | character varying | not null
nameb | jsonb | not null default '{}'::jsonb
So that nameb will became {"en": "$name"} where $name is a value in name field.
For example:
SELECT name, nameb
before:
name | nameb
--------------------------------------+------------
hello | {}
world | {}
after:
name | nameb
--------------------------------------+------------
hello | {"en": "hello"}
world | {"en": "world"}
With regualar types I can do UPDATE SET whatever = (SELECT ...), but How to do this with jsonb?
UPDATE merchants SET nameb = (SELECT '{"en": "fillme!"}'::jsonb); works, but how to set "fillme!" value from another field?

Answer 1

This can be done with jsonb_build_object function which allows you to build json objects from simple data types.
So to do what you want:
update merchants set nameb = nameb || jsonb_build_object('en', name)
With json_build_object we are making {"en": "hello"}, {"en": "world"} ..dynamically based on value from "name" column.
After that we can simply concat to jsonb values with || operator.
This will not work if nameb is NULL because NULL will "eat" everything and result will be NULL again.
In that case I'd suggest to use COALESCE:
update merchants set nameb = COALESCE(nameb, '{}') || jsonb_build_object('en', name)
The other way to achieve the same is to use jsonb_set function. For this particluar case it's overkill, however it may be handy if you need to set some keys somewhere deeply in json:
update merchants set nameb = jsonb_set(nameb, '{en}', ('"' || name || '"')::jsonb)
This looks weird because we have to construct string surrounded of quotes , i.e: '"hello"' to set it as value for 'en' key. In case if you need to set some json, jsonb_build_object is more handy.

Answer 2

I found solution:
UPDATE merchants AS m1
SET nameb = (
SELECT row_to_json(t) FROM (
SELECT name as en FROM merchants AS m2 WHERE m1.id = m2.id
) t
)::jsonb;
Not sure if it's right, but it works

Answer 3

Yes, jsonb_build_object is best choice.
UPDATE merchants
SET nameb = jsonb_build_object('en', "name",
'cs', '')
WHERE ...
create
name | nameb
--------------------------+------------------------------
hello | {"en": "hello", "cs": ""}
world | {"en": "world", , "cs": ""}