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From: David E. Wheeler <[email protected]>
To: Erik Wienhold <[email protected]>
Cc: [email protected]
Subject: Re: JSON Path and GIN Questions
Date: Sat, 16 Sep 2023 16:26:07 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

On Sep 12, 2023, at 21:00, Erik Wienhold <[email protected]> wrote:

>> If so, I’d like to submit a patch to the docs talking about this, and
>> suggesting the use of jsonb_path_query() to test paths to see if they return
>> a boolean or not.
> 
> +1

I’ve started work on this; there’s so much to learn! Here’s a new example that surprised me a bit. Using the GPS tracker example from the docs [1] loaded into a `:json` psql variable, this output of this query makes perfect sense to me:

david=# select jsonb_path_query(:'json', '$.track.segments.location[*] ? (@ < 14)');
 jsonb_path_query
------------------
 13.4034
 13.2635

Because `[*]` selects all the values. This, however, I did not expect:

david=# select jsonb_path_query(:'json', '$.track.segments.location ? (@[*] < 14)');
 jsonb_path_query
------------------
 13.4034
 13.2635
(2 rows)

I had expected it to return two single-value arrays, instead:

 [13.4034]
 [13.2635]

It appears that the filter expression is doing some sub-selection, too. Is that expected?

Best,

David

  [1]: https://www.postgresql.org/docs/current/functions-json.html#FUNCTIONS-SQLJSON-PATH


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