How we can convert string to a date in oracle database?

Answer 1

AFAIK There is no DATETIME format in Oracle and you can use TO_DATE(date_col, 'YYYY-MM-DD HH24:MI:SS AM') or something similar to convert a string to date.

Example

TO_DATE('2011-07-28T23:54:14Z',  'YYYY-MM-DD"T"HH24:MI:SS"Z"')

Answer 2

SELECT CONVERT(DATE,'17/11/2014',103)