Postgres sql: Building a nested json structure on a single table?

Question

I am trying to build a nested Json structure from a single table.

I am trying to get the final result to look like:

[
    {
        "contract_number":"GS00F0XXX",
        'category': [
            {
                'cat_id': "874 1",
                'socio': {
                    "eighta":false,
                    "sdvosb":false,
                    "edwosb":false
                }   
            },
            {
                "cat_id":"874 6",
                'socio': {
                    "eighta":false,
                    "sdvosb":false,
                    "edwosb":false,
                }
            }
        ]
    },
    {
        'contract_number': "GS00Q14OAXXX",
        'category': [
            {
                'cat_id': 'OASIS POOL1',
                'socio': ...
            }
        ]
    }  
]

The underlying table looks something like:

contract_type   contract_number duns_number eighta  sdvosb  edwosb  category
MOBIS           GS00F0XXX       5555555     FALSE   FALSE   FALSE   874 1
MOBIS           GS00F0XXX       5555555     FALSE   FALSE   FALSE   874 6
MOBIS           GS00F0XXX       5555555     FALSE   FALSE   FALSE   874 7
OASIS           GS00Q14OAXXX    5555555     FALSE   FALSE   FALSE   OASIS POOL1
OASIS           GS00Q14OAXXX    5555555     FALSE   FALSE   FALSE   OASIS POOL2

I've tried this query, but it puts everything on two rows, and every time I try to nest a json_agg call I get an error about nestng aggregation functions.

select 
    json_build_object(
        'contract_number', contract_number,
        'info', json_agg(
            json_build_object(
                    'category_id', category,
                    'eighta',eighta,
                    'sdvosb',sdvosb,
                    'edwosb',edwosb
                )
        )
    )
from contract_vehicle
group by duns_number, contract_number

This results in SQL Error [42803]: ERROR: aggregate function calls cannot be nested

select 
    json_build_object(
        'contract_number', contract_number,
        'info', json_agg(
            json_build_object(
                    'category_id', category,
                    'socio', jsonb_agg(
                        json_build_object(
                            'eighta',eighta,
                            'sdvosb',sdvosb,
                            'edwosb',edwosb
                        )
                    )
                )
        )
    )
from contract_vehicle
group by duns_number, contract_number

@SABER - FICTIONAL CHARACTER json_build_object() is supported on 9.4 or newer — Sorix
– Sorix, Commented Oct 31, 2018 at 15:23

SABER · Accepted Answer · 2018-10-31 13:50:08Z

1

I am not sure this will work but give it a try :)

with cte as (
    select  json_agg(
                        json_build_object(
                            'eighta',eighta,
                            'sdvosb',sdvosb,
                            'edwosb',edwosb
                        )
                    ) a1,duns_number dn, contract_number cn
    from contract_vehicle
    group by duns_number, contract_number)
select json_build_object(
        'contract_number'::text, contract_number::text,
        'info'::text, json_agg(
            json_build_object(
                    'category_id'::text, category::text,
                    'socio'::text, a1
                )
        )
    )
from contract_vehicle inner join cte on (duns_number=dn and contract_number = cn)
group by duns_number, contract_number;

edited Oct 31, 2018 at 13:50

answered Oct 31, 2018 at 13:44

SABER

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2 Comments

spitfiredd Over a year ago

I it still giving me the two contract# on two rows. I think I have to build an additional cte that nests inside the one you wrote. I think with your example I can figure it out.

SABER Over a year ago

I'm glad it helped. FYI- You can use string_agg() over() function to merge the two rows accordingly.

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