sql server 查询存储过程返回值

SET QUOTED_IDENTIFIER ON
SET ANSI_NULLS ON
GO

CREATE proc [dbo].[is_yy]
@return_value varchar(2) out,
@p1 varchar(20),
@p2 varchar(50)
as
begin
    if @p1='1'
    begin
          SET @return_value = '1'
    RETURN @return_value
    end
    if @p2='1'
    begin
          SET @return_value = '2'
    RETURN @return_value
    end


end

GO    

DECLARE @return_value1 VARCHAR(50)
EXEC @return_value1 =is_yy '', '1',''
SELECT @return_value1

DECLARE @return_value2 VARCHAR(50)
EXEC @return_value2 =is_yy '', '','1'
SELECT @return_value2