How to query nested arrays in a postgres json column? - sql

Question

I have some json similar to the json below stored in a postgres json column. I'm trying query it to identify some incorrectly entered data. I'm basically looking for addresses where the house description is the same as the house number. I can't quite work out how to do it.
{
"timestamp": "2014-10-23T16:15:28+01:00",
"schools": [
{
"school_id": "1",
"addresses": [
{
"town": "Birmingham",
"house_description": "1",
"street_name": "Parklands",
"addr_id": "4",
"postcode": "B5 8KL",
"house_no": "1",
"address_type": "UK"
},
{
"town": "Plymouth",
"house_description": "Flat a",
"street_name": "Fore Street",
"addr_id": "2",
"postcode": "PL9 8AY",
"house_no": "15",
"address_type": "UK"
}
]
},
{
"school_id": "2",
"addresses": [
{
"town": "Coventry",
"street_name": "Shipley Way",
"addr_id": "19",
"postcode": "CV8 3DL",
"house_no": "662",
"address_type": "UK"
}
]
}
]
}
I have written this sql which will find where the data matches:
select *
FROM title_register_data
where address_data->'schools'->0->'addresses'->0->>'house_description'=
address_data->'schools'->0->'addresses'->0->>'house_no'
This obviously only works on the first address on the first school. Is there a way of querying all of the addresses of every school?

Answer 1

Use jsonb_array_elements() in lateral, join as many times as the depth of a json array which elements you want to compare:
select
schools->>'school_id' school_id,
addresses->>'addr_id' addr_id,
addresses->>'house_description' house_description,
addresses->>'house_no' house_no
from title_register_data,
jsonb_array_elements(address_data->'schools') schools,
jsonb_array_elements(schools->'addresses') addresses
where addresses->>'house_description' = addresses->>'house_no';
school_id | addr_id | house_description | house_no
-----------+---------+-------------------+----------
1 | 4 | 1 | 1
(1 row)