Syntax error in solution for "Stored Procedure ProjektZuteilen für das AngProj-Projekt"

Context

Stored Procedures, exercise 5

Summary

(Summarize the issue encountered concisely)

Steps to reproduce

Try to run the following on DB AngProj schema public:

CREATE OR REPLACE FUNCTION AngInProjekt (AngId IN INTEGER, ProjId IN INTEGER)
RETURNS INTEGER AS $$
DECLARE
    p_n Projektzuteilung.ProjNr%TYPE:=-1;
BEGIN
  SELECT (ProjNr, -1) INTO p_n
    FROM ProjektZuteilung
    WHERE PersNr = AngId AND ProjNr = ProjId;
  RETURN p_n;
END;
$$ LANGUAGE plpgsql;

SELECT AngInProjekt(1001, 26);

What is the current issue behavior?

ERROR:  invalid input syntax for integer: "(26,-1)"
CONTEXT:  PL/pgSQL function anginprojekt(integer,integer) line 5 at SQL statement

********** Error **********

ERROR: invalid input syntax for integer: "(26,-1)"
SQL state: 22P02
Context: PL/pgSQL function anginprojekt(integer,integer) line 5 at SQL statement

What is the expected correct behavior?

(unsure. Some integer, I guess?)

Relevant logs and/or screenshots

(none)

Possible fixes

it happens here

Removing the parentheses seems to solve the problem, but I don't understand the code. Are two columns being selected here? If so, how can they be crammed into a single INTEGER return value? Should there be a COALESCE?

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