Re: Extracting data from jsonb array?

On Mon, Dec 7, 2020 at 4:00 PM David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
wrote:

> On Mon, Dec 7, 2020 at 4:49 PM Ken Tanzer <ken(dot)tanzer(at)gmail(dot)com> wrote:
>
>>
>>
>> On Mon, Dec 7, 2020 at 3:22 PM David G. Johnston <
>> david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>>
>>> On Mon, Dec 7, 2020 at 4:13 PM Steve Baldwin <steve(dot)baldwin(at)gmail(dot)com>
>>> wrote:
>>>
>>>> Try:
>>>>
>>>> select _message_body->'Charges'->>'Name' from ...
>>>>
>>>
>>> Not so much..."Charges" is an array so "->>" doesn't do anything useful.
>>>
>>> The OP needs to use "json_array_elements" to navigate past the array and
>>> get to the next layer of the json where ->>'Name' will then work.
>>>
>>>
>> Thank you David. I had tried that function without much luck. But with
>> your inspiration, I made progress and got to this:
>>
>> select
>> _message_exchange_id,jsonb_array_elements(_message_body->'Charges')->>'Name'
>> FROM message_import_court_case WHERE _message_exchange_id = 1296;
>> _message_exchange_id | ?column?
>> ----------------------+--------------------------------------------
>> 1296 | Possession Of Burglary Tools
>> 1296 | Burglary In The Second Degree (Commercial)
>> (2 rows)
>>
>> But what I really want is one line per message, with the charges in an
>> array. I can't seem to find the right syntax to make this work:
>>
>> => select
>> _message_exchange_id,array_agg(jsonb_array_elements(_message_body->'Charges')->>'Name')
>> FROM message_import_court_case WHERE _message_exchange_id = 1296;
>> ERROR: column "message_import_court_case._message_exchange_id" must
>> appear in the GROUP BY clause or be used in an aggregate function
>> LINE 1: select _message_exchange_id,array_agg(jsonb_array_elements(_...
>> ^
>>
>> => select
>> _message_exchange_id,array_agg(jsonb_array_elements(_message_body->'Charges')->>'Name')
>> FROM message_import_court_case WHERE _message_exchange_id = 1296 GROUP BY 1;
>> ERROR: set-valued function called in context that cannot accept a set
>>
>> => select _message_exchange_id,(SELECT
>> array_agg(jsonb_array_elements(_message_body->'Charges')->>'Name')) FROM
>> message_import_court_case WHERE _message_exchange_id = 1296 GROUP BY 1;
>> ERROR: set-valued function called in context that cannot accept a set
>>
>> => select _message_exchange_id,(SELECT
>> array_agg(jsonb_array_elements(_message_body->'Charges')->>'Name')) FROM
>> message_import_court_case WHERE _message_exchange_id = 1296;
>> ERROR: column "message_import_court_case._message_exchange_id" must
>> appear in the GROUP BY clause or be used in an aggregate function
>> LINE 1: select _message_exchange_id,(SELECT array_agg(jsonb_array_el...
>>
>>
>>
> Sub-queries are a simple solution to get around the "set-valued function"
> restriction.
>
> The more direct way is to place the set-valued function in the FROM clause
> where it wants to be, by using LATERAL (the keyword itself can be implied
> when dealing with functions)
>
> select array_agg(e->>'key') from (values
> ('[{"key":"val"},{"key":"val2"}]'::jsonb)) val (v), jsonb_array_elements(v)
> jae (e)
>
> David J.
>
>
OK, let me try asking again. (I'm trying to actually get something that
works.) So given an example like this:

CREATE TEMP TABLE foo (
id INTEGER,
js JSONB
);

INSERT INTO foo (id,js) VALUES (1,
'[
{"key":"r1kval","key2":"r1k2val"},
{"key":"r1kval2","key2":"r1k2val2"}
]');
INSERT INTO foo (id,js) VALUES (2,
'[
{"key":"r2kval","key2":"r2k2val"},
{"key":"r2kval2","key2":"r2k2val2"}
]');

Can anyone help me with a working query (preferably with the least
cumbersome syntax possible!) that would return these values (the key2
values) as array text elements:

id Agg_val
---- ------------------------
1 {r1k2val,r1k2val2}
2 {r2k2val,r2k2val}

(2 rows)

Thank you!

Ken

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