Error on union with order by clause

Question

here is my sql.
i want sort this sql by start_timestamp.
select name,
enumber,
to_char(new_time(start_TimeStamp,'gmt','edt'),'MM/DD/YY HH24:MI:SS'),
ssn
from emp
where
ename = 'joh%'
and
start_TimeStamp9 > TO_DATE('2007-01-15 00:00:01','YYYY-MM-DD HH24:MI:SS')
and end_TimeStamp11 < TO_DATE('2007-01-18 22:59:59','YYYY-MM-DD HH24:MI:SS')
union
select name,
enumber,
to_char(new_time(start_TimeStamp,'gmt','edt'),'MM/DD/YY HH24:MI:SS'),
ssn
from emp
where
ename = 'joh%'
and
start_TimeStamp9 > TO_DATE('2007-01-15 00:00:01','YYYY-MM-DD HH24:MI:SS')
and end_TimeStamp11 < TO_DATE('2007-01-18 22:59:59','YYYY-MM-DD HH24:MI:SS')
union
select name,
enumber,
to_char(new_time(start_TimeStamp,'gmt','edt'),'MM/DD/YY HH24:MI:SS'),
ssn
from emp
where
ename = 'kris%'
and
start_TimeStamp9 > TO_DATE('2007-01-15 00:00:01','YYYY-MM-DD HH24:MI:SS')
and end_TimeStamp11 < TO_DATE('2007-01-18 22:59:59','YYYY-MM-DD HH24:MI:SS')
union
select name,
enumber,
to_char(new_time(start_TimeStamp,'gmt','edt'),'MM/DD/YY HH24:MI:SS'),
ssn
from emp
where
ename = 'wal%'
and
start_TimeStamp9 > TO_DATE('2007-01-15 00:00:01','YYYY-MM-DD HH24:MI:SS')
and end_TimeStamp11 < TO_DATE('2007-01-18 22:59:59','YYYY-MM-DD HH24:MI:SS')
order by 3;
i got this error.
ORA-01785: ORDER BY item must be the number of a SELECT-list expression
start_timestamp is the 3rd column of the sql.
why i am getting this error.
i tried this also.
order by to_char(new_time(start_TimeStamp,'gmt','edt'),'MM/DD/YY HH24:MI:SS');
still i got error.

Answer 1

Also, be ready for a few surprises when you try to sort dates as strings (by using TO_CHAR):
[email protected]> alter session set nls_date_format = 'mm/dd/yyyy hh24:mi:ss';
Session altered.
[email protected]>
[email protected]> --
[email protected]> -- incorrect order
[email protected]> --
[email protected]> select num, dt
  2  from (
  3    select 1 as num, to_char(new_time(to_date('10/12/01 07:20:33',
  4                                              'mm/dd/yy hh24:mi:ss'),'gmt','edt')) as dt from dual
  5    union
  6    select 2, to_char(new_time(to_date('07/22/07 08:10:23',
  7                                       'mm/dd/yy hh24:mi:ss'),'gmt','edt')) as dt from dual
  8    union
  9    select 3, to_char(new_time(to_date('11/29/99 15:34:49',
10                                       'mm/dd/yy hh24:mi:ss'),'gmt','edt')) from dual
11  )
12  order by dt;
       NUM DT
         2 07/22/2007 04:10:23
         1 10/12/2001 03:20:33
         3 11/29/2099 11:34:49
[email protected]>
[email protected]> --
[email protected]> -- correct order
[email protected]> --
[email protected]> select num, dt
  2  from (
  3    select 1 as num, new_time(to_date('10/12/01 07:20:33',
  4                                      'mm/dd/yy hh24:mi:ss'),'gmt','edt') as dt from dual
  5    union
  6    select 2, new_time(to_date('07/22/07 08:10:23',
  7                               'mm/dd/yy hh24:mi:ss'),'gmt','edt') from dual
  8    union
  9    select 3, new_time(to_date('11/29/99 15:34:49',
10                               'mm/dd/yy hh24:mi:ss'),'gmt','edt') from dual
11  )
12  order by dt;
       NUM DT
         1 10/12/2001 03:20:33
         2 07/22/2007 04:10:23
         3 11/29/2099 11:34:49
[email protected]>
[email protected]>I'd say it's best to sort dates as dates always, and never as strings.
isotope