Question

Looking to get record counts for each month. However, several months has no records therefore no row is returned. How can I get a count of 0 for that month?

select months, count(rowid) as counter from (
    select  to_char(date_entered, 'MM') as months
    from mydatatable
    where to_char(date_entered, 'yyyy') = '2011'
     )
group by months
order by months

Result:

Month    Count
01       32
03       12
04       11
06       10
07       222
08       32

Even tried playing with subq select 1,2,3,4,5,6,7,8,9,10,11,12 from dual and could not get it to work. No pivot capability yet… ;(

Answer 1

You’re probably better off storing the 01 to 12 in a table, but the general approach is to use a left join:

Select
  m.Mo,
  Count(t.dateentered)
From (
    Select '01' As Mo From Dual Union All
    Select '02' From Dual Union All
    Select '03' From Dual Union All
    Select '04' From Dual Union All
    Select '05' From Dual Union All
    Select '06' From Dual Union All
    Select '07' From Dual Union All
    Select '08' From Dual Union All
    Select '09' From Dual Union All
    Select '10' From Dual Union All
    Select '11' From Dual Union All
    Select '12' From Dual
  ) m
    Left Outer Join
  mydatatable t
    On
      m.Mo = to_char(t.dateentered, 'MM') And 
      t.dateentered >= DATE'2011-01-01' And
      t.dateentered < DATE'2012-01-01'
Group By
  m.Mo
Order By
  m.Mo

Update used a more index friendly way of restricting the year.

http://sqlfiddle.com/#!4/68085/10