How to pass a table name and column name as params? Answered by LLM :

CREATE OR REPLACE FUNCTION increment(x int, row_id int, table_name text, column_name text)
RETURNS void AS
$$
BEGIN
  EXECUTE format('UPDATE %I SET %I = %I + $1 WHERE id = $2', 
                 table_name, column_name, column_name)
  USING x, row_id;
END;
$$ 
LANGUAGE plpgsql VOLATILE;