Question

I’m trying to build a query from an Oracle 11g database to use in a report. I need to use two tables CONTACT and CONTACT_EXT to get the data from, and compare the total amount of contacts over two date ranges.The tables are joined by ID’s matching.

CONTACT:

ID | DATE
----------
1   12/12/2010
2   12/11/2010
3   14/09/2011

CONTACT_EXT

 ID | TYPE
----------
1   MAIL
2   FAX
3   FAX  

So for example if I set period A to be between 01/01/2010 and 12/12/2010 and period B to be between 01/01/2011 and 11/11/2011

TYPE | PERIOD A | PERIOD B | TOTAL
MAIL   1          0          1
FAX    1          1          2

Answer 1

Just do a self join:

select type,period_a,period_b,period_a+period_b as total
from(
  select type,count(1) as period_a
  from contact_ext
  left join contact
  using(id)
  where date>='20100101' and date<='20101212'
  group by 1
)a
join(
  select type,count(1) as period_b
  from contact_ext
  left join contact
  using(id)
  where date>='20110101' and date<='20111111'
  group by 1
)b
using(type);