Question

Ok, I’m new using this connect by thing. But its always quite useful. I have this small problem you guys might be able to help me…

Given start month (say to_char(sysdate,'YYYYMM')) and end month (say, to_char(add_months(sysdate, 6),'YYYYMM')), want to get the list of months in between, in the same format.

Well, I want to use this into a partitions automation script. My best shot so far (pretty pitiful) yields invalid months e.g.’201034’… (and yea, I know, incredibly inefficient)

Follows the code:

SELECT id
from
    (select to_char(add_months(sysdate, 6),'YYYYMM') as tn_end, to_char(sysdate,'YYYYMM') as tn_start from dual) tabla,
    (select * from
        (Select Level as Id from dual connect by Level <= (Select to_char(add_months(sysdate, 1),'YYYYMM')from dual)) where id > to_char(sysdate,'YYYYMM')) t
Where 
    t.Id between tabla.tn_start and tabla.tn_end

how do I do to make this query return only valid months? Any tips?

cheers mates,

f.

Answer 1

Best way might be to separate out the row generator from the date function. So generate a list from 0 to 6 and calculate months from that. If you want to pass the months in then do that in the with clause

with my_counter as (
  Select Level-1 as id 
  from dual 
  connect by Level <= 7
) 
select to_char(add_months(sysdate, id),'YYYYMM') from my_counter

The example below will allow you to plug in the dates you require to work out the difference.

with my_counter as (
  Select Level-1 as id 
  from dual 
  connect by level <= months_between(add_months(trunc(sysdate,'MM'), 6), 
      trunc(sysdate,'MM')) + 1
) 
select to_char(add_months(trunc(sysdate, 'MM'), id),'YYYYMM') from my_counter