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From: Tom Lane <[email protected]>
To: Alexander Farber <[email protected]>
Cc: pgsql-general <[email protected]>
Subject: Re: How to pass a list of locations (longitude, latitude) to a PostgreSQL/PostGIS stored function?
Date: Tue, 25 Mar 2025 13:07:29 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAADeyWiTu2P1Y_6dPn2E+1AwSvNkwNHmT6UcFStubz0kFh9gtg@mail.gmail.com>
References: <CAADeyWiTu2P1Y_6dPn2E+1AwSvNkwNHmT6UcFStubz0kFh9gtg@mail.gmail.com>

Alexander Farber <[email protected]> writes:
> Then I am trying to add a function, which would receive a series of
> locations (longitude and latitude pairs in microdegrees) and return a list
> of lowercase 2-letter country codes, like "de", "pl", "lv":

>     CREATE OR REPLACE FUNCTION find_countries(locations BIGINT[][])
>     RETURNS TABLE (country TEXT) AS $$

Postgres isn't too friendly to representing a list of locations as
a 2-D array, because we generally don't treat arrays as being
arrays-of-arrays, so unnest produces a set of bigints not a set
of smaller arrays.  You might be best advised to create a composite
type like "location (long bigint, lat bigint)" and use an array of
that.  If you're really hot to use a 2-D array, the only construct
I can think of that's on board with unnesting that the way you need
is plpgsql's FOREACH SLICE syntax:

https://www.postgresql.org/docs/devel/plpgsql-control-structures.html#PLPGSQL-FOREACH-ARRAY

You could probably make a custom version of unnest that uses that
and then keep your query about the same.

			regards, tom lane

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