c#获取存储过程的返回值

CREATE  PROCEDURE [dbo].[Proc_GetInfo]
    @ywdm varchar(10),
    @value varchar(20) output
AS
begin
    set @value=Select top 1 createt From table Where ywdm=@ywdm 
end

var db = DatabaseFactory.CreateDatabase();
var cmd = db.GetStoredProcCommand("Proc_GetInfo");
db.AddInParameter(cmd, "ywdm", DbType.String, mYzm.Ywdm);
db.AddOutParameter(cmd, "@value", DbType.String, 20);
db.ExecuteNonQuery(cmd);
return cmd.Parameters["@value"].Value.ToString();