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Re: Extracting data from jsonb array? - Mailing list pgsql-general

From	Ken Tanzer
Subject	Re: Extracting data from jsonb array?
Date	December 7, 2020 23:48:39
Msg-id	CAD3a31VDRAV8_snO9SbxwJa77=aUJJTcsSvCRnc1v5mG8NqDkA@mail.gmail.com Whole thread Raw
In response to	Re: Extracting data from jsonb array? ("David G. Johnston" <david.g.johnston@gmail.com>)
Responses	Re: Extracting data from jsonb array?
List	pgsql-general

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On Mon, Dec 7, 2020 at 3:22 PM David G. Johnston <david.g.johnston@gmail.com> wrote:

On Mon, Dec 7, 2020 at 4:13 PM Steve Baldwin <steve.baldwin@gmail.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,(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...

Thanks!

Ken