public String getCreditByUID(Statement statement,String UID)//根据用户名获取信用度
	{
		String result = null;
		sql = "select credit from Users where UID = '" + UID +"'";
		try 
		{
			ResultSet rs = statement.executeQuery(sql);
			while (rs.next()) {
				result = rs.getString("credit");
			}
		} 
		catch (SQLException e) 
		{
			System.out.println("Error! (from src/Fetch/Users.getCreditByUID())");
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return result;
	}