数据库专题 to_number（）函数创建，nvl（）函数创建还原

to_number（） (psql)

使用sql输入并执行创建

CREATE OR REPLACE FUNCTION public.to_number(input character varying)
 RETURNS numeric
 LANGUAGE plpgsql
AS $function$
  BEGIN 
    RETURN CAST(input as NUMERIC);
END
$function$
;

nvl() （psql）

类似于java 方法重载，注意参数的不同类型以及返回类型

CREATE OR REPLACE FUNCTION nvl(CHARACTER VARYING, CHARACTER VARYING)
  RETURNS CHARACTER VARYING AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;
------------------------
CREATE OR REPLACE FUNCTION nvl(BOOLEAN, BOOLEAN)
  RETURNS BOOLEAN  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;
------------------------

CREATE OR REPLACE FUNCTION nvl(INTERVAL, INTERVAL)
  RETURNS INTERVAL  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;
------------------------
CREATE OR REPLACE FUNCTION nvl(TIME WITHOUT TIME ZONE, TIME WITHOUT TIME ZONE)
  RETURNS TIME WITHOUT TIME ZONE  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;

------------------------
CREATE OR REPLACE FUNCTION nvl(DATE, DATE)
  RETURNS DATE  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;

------------------------
CREATE OR REPLACE FUNCTION nvl(NUMERIC, NUMERIC)
  RETURNS NUMERIC  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;
------------------------
CREATE OR REPLACE FUNCTION nvl(TIMESTAMP WITHOUT TIME ZONE, TIMESTAMP WITHOUT TIME ZONE)
  RETURNS TIMESTAMP WITHOUT TIME ZONE  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;

 ------------------------

CREATE OR REPLACE FUNCTION nvl(TEXT, TEXT)
  RETURNS TEXT  AS
  $BODY$
  DECLARE

  BEGIN
  	IF $1 IS NOT NULL THEN
  			RETURN $1;
  		ELSE
  			RETURN $2;
  	END IF;
  END;
  $BODY$
  	LANGUAGE 'plpgsql' VOLATILE
  	COST 100;