Postgres 10 and malformatted array literal when using EXECUTE - postgresql

Question

I am trying to create a function on Postgres 10 that would check whether all the given ids exist
in the target table.
CREATE OR REPLACE FUNCTION "public"."has_mismatching_ids"(
_ids TEXT[],
_column_name TEXT,
_table_name TEXT,
_schema_name TEXT DEFAULT 'public'
)
RETURNS BOOLEAN AS
$$
DECLARE
result TEXT[] := '{}';
_query TEXT := '';
BEGIN
IF _ids IS NULL THEN
RETURN false;
END IF;
_query := CONCAT('SELECT UNNEST($1) EXCEPT SELECT "', _column_name, '" FROM "', _schema_name ,'"."', _table_name ,'"');
EXECUTE _query INTO result USING $1;
RAISE NOTICE 'Executed';
IF array_length(result, 1) > 0 THEN
RETURN true;
END IF;
RETURN false;
END;
$$
LANGUAGE plpgsql
STABLE
SECURITY INVOKER;
This is my function that returns correctly true if all the ids exist, but it throws an exception if any of
the ids does not exist.
CREATE TABLE "public"."categories" ("category_id" TEXT NOT NULL PRIMARY KEY);
INSERT INTO "public"."categories" ("category_id") VALUES ('foo');
INSERT INTO "public"."categories" ("category_id") VALUES ('bar');
This works
SELECT FROM "public"."has_mismatching_ids"(ARRAY['foo'], 'category_id', 'categories', 'public');
NOTICE: Executed
has_mismatching_ids
---------------------
f
(1 row)
but this fails to even
SELECT FROM "public"."has_mismatching_ids"(ARRAY['foo2'], 'category_id', 'categories', 'public');
ERROR: malformed array literal: "foo2"
DETAIL: Array value must start with "{" or dimension information.
CONTEXT: PL/pgSQL function public.has_mismatching_ids(text[],text,text,text) line 14 at EXECUTE
and strangely this works also if I write a function that uses explicit names and without EXECUTE
SELECT UNNEST(ARRAY['foo', 'foo3']) EXCEPT SELECT "category_id" FROM "public"."categories";
unnest
--------
foo3
(1 row)
Why doesn't my dynamic function work when comparing to values that do not exist in the target table?

Answer 1

You may use a simple SQL to compare if all array element exists.
CREATE OR replace FUNCTION "public"."has_mismatching_ids"(
_ids text[],
_column_name text,
_table_name text,
_schema_name text DEFAULT 'public' )
returns boolean AS $$
DECLARE res BOOLEAN;
BEGIN
IF _ids IS NULL then
RETURN false;
END IF;
EXECUTE format ( 'SELECT COUNT(*) = cardinality($1)
FROM %I.%I WHERE %I = ANY($2)',
_schema_name,_table_name,_column_name )
INTO res using _ids, _ids;
RETURN res;
END;
$$ language plpgsql stable security invoker;
Demo