Unable to get all the values from JSON_ARRAY_ELEMENTS() - json

Question

Table with sample data:
create table tbl_jsdata
(
id int,
p_id int,
field_name text,
field_value text
);
insert into tbl_jsdata values
(1,101,'Name','Sam'),
(2,101,'City','Dubai'),
(3,101,'Pin','1235'),
(4,101,'Country','UAE'),
(5,102,'Name','Sam'),
(6,102,'City','Dubai'),
(7,102,'Name','Sam Jack'),
(8,102,'Name','Test'),
(9,102,'Name',null);
json_agg query:
drop table if exists tempJSData;
select p_id,
json_build_array(json_object_agg(field_name, field_value)) into tempJSData
from tbl_jsdata
group by p_id;
Getting Result:
select p_id,(json_array_elements(json_build_array)->>'Name')::text Namess
from tempJSData
p_id Namess
---------------------------------
101 Sam
102
Expected Result:
p_id Namess
---------------------------------
101 Sam
102 Sam
102 Sam Jack
102 Test
102

Answer 1

I think it's because you're not creating an array of Name.
If you check your query
select p_id,
json_build_array(json_object_agg(field_name, field_value))
from tbl_jsdata
group by p_id;
The result is
p_id | json_build_array
------+---------------------------------------------------------------------------------------------
101 | [{ "Name" : "Sam", "City" : "Dubai", "Pin" : "1235", "Country" : "UAE" }]
102 | [{ "Name" : "Sam", "City" : "Dubai", "Name" : "Sam Jack", "Name" : "Test", "Name" : null }]
(2 rows)
Having multiple adjacent entries of the Name field. The following json_array_elements(json_build_array)->>'Name' will fetch the first entry only. I suggest to create an array based on p_id and field_name first
with array_built as (
select p_id,field_name,
array_agg(field_value) field_value
from tbl_jsdata
group by p_id, field_name
)
select p_id,
jsonb_object_agg(field_name, field_value)
from array_built
group by p_id
;
The result can be optimised since it creates an array even if there is only one value
p_id | jsonb_object_agg
------+---------------------------------------------------------------------------
101 | {"Pin": ["1235"], "City": ["Dubai"], "Name": ["Sam"], "Country": ["UAE"]}
102 | {"City": ["Dubai"], "Name": ["Sam", "Sam Jack", "Test", null]}
(2 rows)
But now you can parse it correctly the whole query is
select p_id,
json_build_array(json_object_agg(field_name, field_value))
from tbl_jsdata
group by p_id;
select p_id,
json_build_array(json_object_agg(field_name, field_value))
from tbl_jsdata
group by p_id;
with array_built as (
select p_id,field_name,
array_agg(field_value) field_value
from tbl_jsdata
group by p_id, field_name
), agg as (
select p_id,
jsonb_object_agg(field_name, field_value) json_doc
from array_built
group by p_id
)
select p_id, jsonb_array_elements(json_doc->'Name') from agg;
;
With the expected result as
p_id | jsonb_array_elements
------+----------------------
101 | "Sam"
102 | "Sam"
102 | "Sam Jack"
102 | "Test"
102 | null
(5 rows)

Answer 2

You can use json_each_text to extract the values of your array and in the WHERE clause filter only the key you want:
SELECT p_id,j.value
FROM tempJSData, json_each_text(json_build_array->0) j
WHERE j.key = 'Name';
p_id | value
------+----------
101 | Sam
102 | Sam
102 | Sam Jack
102 | Test
102 |
(5 rows)
Note: this query assumes the format of your json is final. If not, consider creating an array of Name instead of an array of objects that contain names in it: name[foo,bar] instead of [name:foo,name:bar]. The answer from Ftisiot makes a pretty good point.
Demo: db<>fiddle

Answer 3

Your JSON aggregation is essentially invalid, as you are creating a JSON value where the same key appears more than once. If you had used the recommended jsonb data type, the duplicate keys would have been removed.
I think this aggregation makes more sense:
create table tempjsdata
as
select p_id,
jsonb_agg(jsonb_build_object(field_name, field_value)) as names
from tbl_jsdata
group by p_id
The above generates the following result:
p_id | names
-----+---------------------------------------------------------------------------------------------
101 | [{"Name": "Sam"}, {"City": "Dubai"}, {"Pin": "1235"}, {"Country": "UAE"}]
102 | [{"Name": "Sam"}, {"City": "Dubai"}, {"Name": "Sam Jack"}, {"Name": "Test"}, {"Name": null}]
Then you can use:
select p_id,
x.*
from tempjsdata
cross join lateral (
select x.item ->> 'Name'
from jsonb_array_elements(t.names) as x(item)
where x.item ? 'Name'
) x
Online example