如何选择 "cat.item.category" Pypark中的列？模式如下：，

root
 |-- result: struct (nullable = true)
 |    |-- active: string (nullable = true)
 |    |-- cat_item.category: struct (nullable = true)
 |    |    |-- display_value: string (nullable = true)
 |    |    |-- link: string (nullable = true)
 |    |-- number: string (nullable = true)
 |    |-- sys_id: string (nullable = true)

我试过下面的方法，但出现了一个错误，

df22 = df22.select("result.active", "result.cat_item.category.display_value", "result.cat_item.category.link", "result.number", "result.sys_id")

如何选择结构列？