Why can't I use a plsql argument in this where clause? - postgresql

Question

I have a function below (is_organizer) that works, and lets me use this method as a computed field in Hasura. The function below (is_chapter_member) which is almost identical, doesn't work.
WORKS
CREATE OR REPLACE FUNCTION is_organizer(event_row events, hasura_session json)
RETURNS boolean AS $$
SELECT EXISTS (
SELECT 1
FROM event_organizers o
WHERE
o.user_id::text = hasura_session->>'x-hasura-user-id'
AND
(event_row.id = o.event_id OR event_row.event_template_id = o.event_template_id)
);
$$ LANGUAGE SQL STRICT IMMUTABLE;
BROKEN
CREATE OR REPLACE FUNCTION is_chapter_member(c chapters, hasura_session json)
RETURNS boolean AS $$
SELECT EXISTS (
SELECT 1
FROM chapter_members m
WHERE
m.user_id::text = hasura_session->>'x-hasura-user-id'
AND
c.chapter_id = m.chapter_id
);
$$ LANGUAGE SQL STRICT IMMUTABLE;
When attempting to add this function (not call it, just create it) Postgres gives me the following error:
ERROR: missing FROM-clause entry for table "c"
LINE 9: c.chapter_id = m.chapter_id
Why would a function param need a where clause? Table dumps below...
Table "public.chapters"
Column | Type | Collation | Nullable | Default
-----------------+--------------------------+-----------+----------+--------------------------------------
id | integer | | not null | nextval('chapters_id_seq'::regclass)
title | text | | not null |
slug | text | | not null |
description | jsonb | | |
avatar_url | text | | |
photo_url | text | | |
region | text | | |
maps_api_result | jsonb | | |
lat | numeric(11,8) | | |
lng | numeric(11,8) | | |
created_at | timestamp with time zone | | not null | now()
updated_at | timestamp with time zone | | not null | now()
deleted_at | timestamp with time zone | | |
Table "public.chapter_members"
Column | Type | Collation | Nullable | Default
------------+--------------------------+-----------+----------+---------
user_id | integer | | not null |
chapter_id | integer | | not null |
created_at | timestamp with time zone | | not null | now()
updated_at | timestamp with time zone | | not null | now()
Table "public.events"
Column | Type | Collation | Nullable | Default
-------------------+-----------------------------+-----------+----------+---------------------------------------------------
id | integer | | not null | nextval('events_id_seq'::regclass)
event_template_id | integer | | not null |
venue_id | integer | | |
starts_at | timestamp without time zone | | not null |
duration | interval | | not null |
title | text | | |
slug | text | | |
description | text | | |
photo_url | text | | |
created_at | timestamp without time zone | | not null | now()
updated_at | timestamp without time zone | | not null | now()
deleted_at | timestamp without time zone | | |
ends_at | timestamp without time zone | | | generated always as (starts_at + duration) stored
Table "public.event_organizers"
Column | Type | Collation | Nullable | Default
-------------------+---------+-----------+----------+----------------------------------------------
id | integer | | not null | nextval('event_organizers_id_seq'::regclass)
user_id | integer | | not null |
event_id | integer | | |
event_template_id | integer | | |

Answer 1

This turned out to be using an incorrect column name in the broken function. chapter_id should have just been id on the c argument. I took Richard's prompt and tried putting parens around the arg like (c).chapter_id. This then correctly told me that chapter_id doesn't exist, and allowed me to fix the issue.