-- 型違いの複数登録が必要
CREATE OR REPLACE FUNCTION nvl(expr1 text, expr2 text)
  RETURNS text AS
$BODY$
  SELECT coalesce($1, $2);
$BODY$
  LANGUAGE sql;
  
CREATE OR REPLACE FUNCTION nvl(expr1 date, expr2 date)
 RETURNS date AS
$BODY$
 SELECT coalesce($1, $2);
$BODY$
 LANGUAGE sql;

CREATE OR REPLACE FUNCTION nvl(expr1 numeric, expr2 integer)
 RETURNS numeric AS
$BODY$
 SELECT coalesce($1, $2);
$BODY$
 LANGUAGE sql;

CREATE OR REPLACE FUNCTION nvl(expr1 text, expr2 integer)
  RETURNS integer AS
$BODY$
  SELECT COALESCE(cast($1 as int), $2);
$BODY$
  LANGUAGE SQL;

CREATE OR REPLACE FUNCTION nvl(expr1 NUMERIC, expr2 text)
  RETURNS text AS
$BODY$
  SELECT COALESCE($1||'', $2);
$BODY$
  LANGUAGE SQL;