Postgres 13

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CREATE OR REPLACE FUNCTION myfunc(int)

RETURNS TABLE(val int, txt text) LANGUAGE 'plpgsql'

AS $$

BEGIN

CREATE TEMPORARY TABLE tmp(id int,res text) ON COMMIT DROP;

IF $1=0 THEN

INSERT INTO tmp VALUES ($1,'Invalid');

ELSE

FOR i IN 1..$1 LOOP

INSERT INTO tmp VALUES (i,'txt '||i);

END LOOP;

END IF;

RETURN QUERY SELECT id,res FROM tmp;

END;

$$;

SELECT * FROM myfunc(42);