How to format and sort a date in Oracle?

Question

In my application am trying to format and sort the date, i am using to_char() function to format the date to my required format, but when i sort them it is sorting

Answer 1

It sounds like you want something like

SELECT to_char( your_date_column, your_format_mask )
  FROM your_table
 ORDER BY your_date_column

In the SELECT list, you want to return a character string that represents the date in your preferred format. In the ORDER BY clause, you want to order by the actual date. Using the standard EMP and DEPT tables, for example

SQL> ed
Wrote file afiedt.buf

  1  select to_char( hiredate, 'DD-MM-YYYY' )
  2    from emp,
  3         dept
  4   where emp.deptno = dept.deptno
  5*  order by hiredate
SQL> /

TO_CHAR(HI
----------
17-12-1980
20-02-1981
22-02-1981
02-04-1981
01-05-1981
09-06-1981
08-09-1981
28-09-1981
17-11-1981
03-12-1981
03-12-1981
23-01-1982
19-04-1987
23-05-1987

14 rows selected.

If you add a DISTINCT, the problem is that Oracle doesn't know that the function you are applying (in this case TO_CHAR) provides a one-to-one mapping from the data in the table to the data in the output. For example, two different dates (October 1, 2010 10:15:15 and October 1, 2010 23:45:50) might generate the same character output, forcing Oracle to eliminate one of the two '01-10-2010' strings but the two dates would sort differently. You can rectify that problem by nesting your query and converting the string back to a date after doing the DISTINCT and before doing the ORDER BY

SQL> ed
Wrote file afiedt.buf

  1  select hire_date_str
  2    from (
  3      select distinct to_char( hiredate, 'DD-MM-YYYY' ) hire_date_str
  4        from emp,
  5             dept
  6       where emp.deptno = dept.deptno
  7      )
  8*  order by to_date(hire_date_str,'DD-MM-YYYY')
SQL> /

HIRE_DATE_
----------
17-12-1980
20-02-1981
22-02-1981
02-04-1981
01-05-1981
09-06-1981
08-09-1981
28-09-1981
17-11-1981
03-12-1981
23-01-1982
19-04-1987
23-05-1987

13 rows selected.