Ejemplo 1 (cont.)

CREATE OR REPLACE FUNCTION
  suma(INTEGER, INTEGER)
  RETURNS INTEGER
  LANGUAGE SQL
  CALLED ON NULL INPUT
  AS '
    SELECT CASE
      WHEN $1 IS NULL THEN
        CASE
          WHEN $2 IS NULL THEN NULL
          ELSE $2
        END
      WHEN $2 IS NULL THEN $1
      ELSE $1 + $2
    END'
  IMMUTABLE;