PSQL - Modifying JSONB element - postgresql

Question

I have a jsonb object like this:
{
"members": [
[
"1966-07-31",
null,
{
"last_name": "ss",
"first_name": "ss"
}
],
[
"1968-12-17",
"spouse",
{
"last_name": "kk",
"first_name": "kk"
}
]
]
}
I want to convert it to.
{
"applicants": [
{
"last_name": "ss",
"first_name": "ss"
}
{
"last_name": "kk",
"first_name": "kk"
}
]
}
Essentially taking the third element of each member and putting is an object in a new array 'applicant'. I don't need the member data that is outside the object.
I can run a PHP script to loop through all the rows and update it. But I'm wondering if I can write this in plain sql query?
Thanks.

Answer 1

You should use jsonb_array_elements with two CROSS JOIN for extract JSON array data then aggregate them
Dynamic array:
Demo
select
jsonb_build_object('applicants', jsonb_agg(e2.value))
from
test t
cross join jsonb_array_elements(t.obj -> 'members') as e1
cross join jsonb_array_elements(e1.value) as e2
where
e2.value ? 'first_name'
and e2.value ? 'last_name'
Static array:
If your structure is specific you don't need a loop over the array and can use the below query:
Demo
select
jsonb_build_object('applicants', jsonb_agg(e1.value -> 2))
from
test t
cross join jsonb_array_elements(t.obj -> 'members') as e1