oracle 查询问题，将’1999-8-5 23:44:34’字符串 分别截取时、分、秒

用oracle的substr函数.substr(字段名,起始位置(从0开始),位数).
例:ts = '2008-01-17 17:08:38'
select t.ts ,
substr(t.ts,12,2) AS hour ,
substr(t.ts,15,2) AS minute ,
substr(t.ts,18,2) AS second
from table t

结果就是:17,08,38
但我这里的ts的类型是char型.

to_date('21/01/2002 5:02:23 pm' ,'dd/mm/yyyy hh:mi:ss am')