oracle collection 的疑问

下面语句均不行

fn_split('4,5,6,78',',') 返回的是 collection

select fn_split('4,5,6,78',',')[0] from dual
select fn_split('4,5,6,78',',').first from dual

我想取集合中的第一个字符串 1 请问有什么办法?

SELECT * FROM TABLE (CAST (fn_split('4,5,6,78',',') AS ty_str_split)) where rownum < 2;