Postgresql function doesn't return anything when UUID argument is used in WHERE clause - postgresql

Question

I'm pretty new to Postgresql. The issue I'm having is that I have a function that returns a table, but when I pass an UUID which is used in the where clause, it returns nothing. The funny thing is that if I take the SQL statement inside the function and run it by itself in PgAdmin, it gives me the right result.
The function looks like the following:
CREATE OR REPLACE FUNCTION get_service (
service_id uuid ) RETURNS TABLE(id uuid,title text,description text,category text,photo_url text,address text,
created_by uuid,created_on timestamp,service_rating float,rating_count bigint) AS $func$
Select
service.id,
service.title,
service.description,
service.category,
service.photo_url,
service.address,
service.created_by,
service.created_on,
CAST(AVG(rating.rating) AS float) as service_rating,
Count(rating.rating) as rating_count
from service
left join rating_service_map map
on service.id = map.service_id
left join rating
on rating.id = map.rating_id
where service.id = service_id
group by service.id,service.title,service.description,service.category,service.photo_url,service.address,service.created_by,service.created_on;
$func$ LANGUAGE SQL;
I have two records in my service table. The ID is of the type uuid and has a default value of uuid_generate_v4(). One of the records has an id of '2af3f03e-b2e5-44fd-89e8-3dc5fb641732'
If I run this I get no result:
select * from get_service('2af3f03e-b2e5-44fd-89e8-3dc5fb641732')
But if I run the following statement (the SQL portion of the function), then I get my right result:
Select
service.id,
service.title,
service.description,
service.category,
service.photo_url,
service.address,
service.created_by,
service.created_on,
CAST(AVG(rating.rating) AS float) as service_rating,
Count(rating.rating) as rating_count
from service
left join rating_service_map map
on service.id = map.service_id
left join rating
on rating.id = map.rating_id
where service.id = '2af3f03e-b2e5-44fd-89e8-3dc5fb641732'
group by service.id,service.title,service.description,service.category,service.photo_url,service.address,service.created_by,service.created_on;
I've also tried to cast the service_id (I've tried "where service.id = sevice_id::uuid" and "where service.id = CAST(service_id AS uuid)") but none of them worked.
I really appreciate it if you can tell me what I'm doing wrong. I've been at this for a couple of hours now.
Thank you.

Answer 1

I suspect that it's because the identifier service_id is ambiguous, being present as both a function parameter and a column in the map table.
Unlike a plain query, where such ambiguity would result in an error, conflicts in SQL functions are resolved by giving precedence to the column, so service_id in your case is actually referring to map.service_id.
You can either qualify it in your function body using the name of your function (i.e. get_service.service_id), or simply choose another name for the parameter.