Unpacking JSON Into Flat Format - json

Question

I have JSON that resembles the following:
{
"ANNOTATIONS": [
{
"Label": "CommingledProduct",
"Text": "NBP"
},
{
"Label": "CommingledVenue",
"Text": "OTC"
}
]
}
I need to unpack this into a flat table with columns matching the annotation labels. So columns based on the above json become:
comingled_product
comingled_venue
The JSON is coming from a json field in a source table and being unpacked into another table.
I know that I could code as follows:
INSERT INTO my_target_table (comingled_product, comingled_venue)
SELECT
payload->'ANNOTATIONS'->0->>'Text',
payload->'ANNOTATIONS'->1->>'Text'
FROM my_source_table;
However, I would rather not use the ordinals of the annotations. I would prefer to use some syntax mirroring the psuedo-code below:
INSERT INTO my_target_table (comingled_product, comingled_venue)
SELECT
payload->'ANNOTATIONS'->'label="ComingledProduct"'->>'Text',
payload->'ANNOTATIONS'->'label="ComingledVenueID"'->>'Text'
FROM my_source_table;
Can anyone tell me if what I'm trying to ahcieve is possible and how to do it? There are more than the two annotations I have included in the sample, so anything that involves multiple joins is probably a no go.
Using PostGres 10.7

Answer 1

demo:db<>fiddle
WITH cte AS (
SELECT
elems.value
FROM
my_source_table,
json_array_elements(payload -> 'ANNOTATIONS') elems
)
SELECT
(SELECT value ->> 'Text' FROM cte WHERE value ->> 'Label' = 'CommingledProduct'),
(SELECT value ->> 'Text' FROM cte WHERE value ->> 'Label' = 'CommingledVenue')
Expanding the array into one row per array element and store this result for further usage into a CTE
This result can be used to query the expected values (without doing the expanding twice)
Could be a little bit faster:
demo:db<>fiddle
SELECT
payload,
MIN(the_text) FILTER (WHERE label = 'CommingledProduct'),
MIN(the_text) FILTER (WHERE label = 'CommingledVenue')
FROM (
SELECT
payload::text AS payload,
elems ->> 'Label' AS label,
elems ->> 'Text' AS the_text
FROM
my_source_table,
json_array_elements(payload -> 'ANNOTATIONS') elems
) s
GROUP BY payload

Answer 2

The answer from #S-Man is great and you should use that for your postgres 10.7. json_path will be added in postgres 12, which will allow you to do something a little bit closer to your pseudo-code, but only with jsonb (not json):
INSERT INTO my_target_table (comingled_product, comingled_venue)
SELECT jsonb_path_query(payload,
'$.ANNOTATIONS[*] ? (#.Label == "CommingledProduct")')->>'Text',
jsonb_path_query(payload,
'$.ANNOTATIONS[*] ? (#.Label == "CommingledVenue")')->>'Text'
FROM my_source_table;
The jsonb_path_query syntax takes a bit to figure out, but it is basically returning elements of the ANNOTATIONS array for which the Label equals either CommingledProduct or CommingledVenue. jsonb_path_query returns a jsonb object, so we can use the ->> operator to grab the value of 'Text' from the object.