for the right syntax to use near '?where id=?'，利用javaWeb做项目时出现前面的状况，这是什么问题？

Question

代码：Connection conn =DBHelper.getConnection(); String sql = "update userinfo set balance=?"+"where id=?"; PreparedStatement ps = (PreparedStatement) conn.prepareStatement(sql); ps.setDouble(1, balance); ps.setInt(2, id); ps.executeUpdate(sql);

Answer 1

问号和where连起来了，拼接后是?where，中间需要一个空格