How to write a query with group by and order by for a date column

Question

I have a query:
select count(*), to_char(s.pdate,'Mon-yyyy') as month from sTable s
group by to_char(s.pdate,'Mon-yyyy')
order by to_date(s.pdate,'Mon-yyyy')
However, I got an error: not a GROUP By expression.
If i just run: select count(*), to_char(s.pdate,'Mon-yyyy') as month from sTable s
group by to_char(s.pdate,'Mon-yyyy')
it is work fine.
How to solve the problem.
Thanks,
Jen

Answer 1

Jen,
You can use this code
with sTable as (select to_date('01/01/2009', 'dd/mm/yyyy') pdate,  1 code from dual union all
              select to_date('02/02/2009', 'dd/mm/yyyy') a, 2 code from dual union all
              select to_date('01/03/2009', 'dd/mm/yyyy') d, 3 code from dual union all
              select to_date('05/04/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/05/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/06/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/07/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/08/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/09/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/10/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/11/2009', 'dd/mm/yyyy') g, 4 code from dual union all
              select to_date('05/12/2009', 'dd/mm/yyyy') h, 5 code from dual)
select cnt, to_char(to_date(mnt||'01', 'yyyymmdd'), 'Mon-yyyy')
  from (select count(*) cnt, to_char(s.pdate,'yyyymm') as mnt
          from sTable s
         group by to_char(s.pdate,'yyyymm')
         order by to_char(s.pdate,'yyyymm')
       CNT MONTH
         1 Jan-2009
         1 Feb-2009
         1 Mar-2009
         1 Apr-2009
         1 May-2009
         1 Jun-2009
         1 Jul-2009
         1 Aug-2009
         1 Sep-2009
         1 Oct-2009
         1 Nov-2009
         1 Dec-2009
12 rows selectedyour problem was that you are using a expresión in the order by (to_date...) that is distinct to the query results (to_char...).
Regards,
Mike