Postgres 13

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-- CREATE EXTENSION intarray;  -- already pre-installed on dbfiddle

CREATE TABLE users (id serial, row_status text DEFAULT 'new', updated_by text);
INSERT INTO users DEFAULT VALUES;
INSERT INTO users DEFAULT VALUES;
INSERT INTO users DEFAULT VALUES;

TABLE users ORDER BY id;
1 rows affected

1 rows affected

1 rows affected



id
row_status
updated_by


1
new
null

2
new
null

3
new
null


CREATE OR REPLACE FUNCTION f_update_status(_ids_as_string text = NULL, _status text = NULL)
   RETURNS text
   LANGUAGE plpgsql AS
$func$
DECLARE
   _ids     int[] := string_to_array(_ids_as_string, ',')::int[];  -- leadig and trailing white space is trimmed from integers automatically
   _updated int[];
BEGIN
   WITH upd AS (
      UPDATE users
      SET    row_status = _status
           , updated_by = 'hxBiSP'
      WHERE  id = ANY (_ids)  -- just use input array; only existing IDs are affected
      RETURNING id            -- return actually affected IDs
      )
   SELECT ARRAY(TABLE upd) INTO _updated; -- aggregate into array with ARRAY constructor

   RETURN format('Updated: %s. Not found: %s.'
        , _updated::text
        , (_ids - _updated)::text);
END
$func$;
-- just to demonstrate that leading and dangling white is not problem
SELECT f_update_status('  12, 4 ,55,  56 ', 'updated');


f_update_status


Updated: {}. Not found: {4,12,55,56}.


SELECT f_update_status('1,2,5', 'updated');


f_update_status


Updated: {1,2}. Not found: {5}.


TABLE users ORDER BY id;


id
row_status
updated_by


1
updated
hxBiSP

2
updated
hxBiSP

3
new
null