Grouping date of births in 2 month periods - mysql

Question

I'm running a simple query that's returning the number of children turning 2 (birthday last month or next month). The following query returns a single row with count:
SELECT COUNT(*)
FROM table AS t
-- Child turning 2
AND t.dob <= DATE_SUB(NOW(), INTERVAL 23 MONTH)
AND t.dob >= DATE_SUB(NOW(), INTERVAL 25 MONTH)
I'd like to be able to build on this query and return multiple count rows, each for a 2 month period so that I can predict 2nd birthdays moving forward.
I could do something like this:
SELECT COUNT(*)
FROM table AS t
-- Child turning 2
AND t.dob <= DATE_SUB(NOW(), INTERVAL 23 MONTH)
AND t.dob >= DATE_SUB(NOW(), INTERVAL 25 MONTH)
UNION
SELECT COUNT(*)
FROM table AS t
-- Child turning 2
AND t.dob <= DATE_SUB(NOW(), INTERVAL 21 MONTH)
AND t.dob >= DATE_SUB(NOW(), INTERVAL 23 MONTH)
UNION...
But this is stupidly inefficient and very clumsy.
As an output I'd like to see something like this:
count |date range
---------------------------------
327 |2012-03-01 - 2012-04-31
---------------------------------
532 |2012-05-01 - 2012-06-31
I think I need to do something with GROUP BY but am unsure about how to go about this.
Many thanks.

Answer 1

select
case
when t.dob between date_sub(now(), interval 25 month) and date_sub(now(), interval 23 month) then 'between -25 and -23 month'
when t.dob between date_sub(now(), interval 22 month) and date_sub(now(), interval 20 month) then 'between -22 and -20 month'
when t.dob between date_sub(now(), interval 19 month) and date_sub(now(), interval 17 month) then 'between -19 and -17 month'
when t.dob between date_sub(now(), interval 16 month) and date_sub(now(), interval 14 month) then 'between -16 and -14 month'
end as my_ranges,
count(*)
from
t
group by my_ranges