Extract json key/value pairs with postgresql/snowflake, where value is not null/blank - postgresql

Question

I have a field called "filter" with json array like:
[
{
"after":"2021-10-14T00:00:00",
"column":"createddate",
"from":null,
"gt":null,
"gte":null,
"id":"928d57b0",
"lt":null,
"lte":null,
"not":null,
"prior":null,
"to":null,
"value":null
},
{
"after":null,
"column":"last_coach_date",
"from":"",
"gt":null,
"gte":null,
"id":"01704cdd",
"lt":null,
"lte":null,
"not":null,
"prior":null,
"to":"",
"value":null
}
]
I'm trying to extract key/value pairs where value is not null/blank and create another field for it.
Maybe to something like this or one long string:
{ "after": "2021-10-14T00:00:00", "column": "createddate", "id": "928d57b0"}, {"column": "last_coach_date","id": "01704cdd"} AS filter_value

Answer 1

Using FLATTEN and OBJECT_AGG:
CREATE OR REPLACE TABLE t(col VARIANT)
AS
SELECT PARSE_JSON('[ { "after": "2021-10-14T00:00:00", "column": "createddate", "from": null, "gt": null, "gte": null, "id": "928d57b0", "lt": null, "lte": null, "not": null, "prior": null, "to": null, "value": null }, { "after": null, "column": "last_coach_date", "from": "", "gt": null, "gte": null, "id": "01704cdd", "lt": null, "lte": null, "not": null, "prior": null, "to": "", "value": null }]'
);
Query:
SELECT s.index, OBJECT_AGG(s2.key, s2.value) AS output
FROM t
,LATERAL FLATTEN(input => col) s
,LATERAL FLATTEN(input => s.value) s2
WHERE NOT IS_NULL_VALUE(s2.value) AND s2.value::TEXT != ''
GROUP BY s.INDEX;
Output:

Answer 2

For Postgres:
select (select jsonb_object_agg(key, value)
from jsonb_array_elements(t.filter) as x(item)
cross join jsonb_each_text(x.item) as e(key,value)
where e.value <> '')
from the_table t;

Answer 3

So very similar to Lukasz solution, but OBJECT_AGG will filter out any NULL values, so if you cast to ::text the nulls become real nulls, and are filtered out, so the WHERE clause is not required:
WITH data_table AS(
SELECT parse_json('[ { "after": "2021-10-14T00:00:00", "column": "createddate", "from": null, "gt": null, "gte": null, "id": "928d57b0", "lt": null, "lte": null, "not": null, "prior": null, "to": null, "value": null }, { "after": null, "column": "last_coach_date", "from": "", "gt": null, "gte": null, "id": "01704cdd", "lt": null, "lte": null, "not": null, "prior": null, "to": "", "value": null } ]') as json
)
SELECT f.index as batch_id,
OBJECT_AGG(p.key, NULLIF(p.value::text,'')::variant) as obj
FROM data_table t,
TABLE(FLATTEN(input=>t.json)) as f,
TABLE(FLATTEN(input=>f.value)) as p
GROUP BY 1
ORDER BY 1
;
gives:
BATCH_ID
OBJ
0
{ "after": "2021-10-14T00:00:00", "column": "createddate", "id": "928d57b0" }
1
{ "column": "last_coach_date", "id": "01704cdd" }
It's not clear from the question if you want 2 rows, or a single value, the latter can be had by adding another layer of aggregation via ARRAY_AGG:
WITH data_table AS(
SELECT parse_json('[ { "after": "2021-10-14T00:00:00", "column": "createddate", "from": null, "gt": null, "gte": null, "id": "928d57b0", "lt": null, "lte": null, "not": null, "prior": null, "to": null, "value": null }, { "after": null, "column": "last_coach_date", "from": "", "gt": null, "gte": null, "id": "01704cdd", "lt": null, "lte": null, "not": null, "prior": null, "to": "", "value": null } ]') as json
)
SELECT array_agg(obj) as single_answer
FROM (
SELECT f.index as batch_id,
OBJECT_AGG(p.key, NULLIF(p.value::text,'')::variant) as obj
FROM data_table t,
TABLE(FLATTEN(input=>t.json)) as f,
TABLE(FLATTEN(input=>f.value)) as p
GROUP BY 1
)
;
gives:
SINGLE_ANSWER
[ { "after": "2021-10-14T00:00:00", "column": "createddate", "id": "928d57b0" }, { "column": "last_coach_date", "id": "01704cdd" } ]