interval by 4 using sql - Mysql -

i've table , want data interval 4 or, when i'm using modulo record not expected, pfb `

select (date_format(subscribed_from, '%y-%m')) date_ subscription operator = 'tim' , date_format(subscribed_from, '%y-%m-%d') between  '2013-01-01' , '2014-12-31' group (date_format(subscribed_from, '%y-%m')); 

it show record this

2013-01  2013-02  2013-03  2013-04  2013-05  2013-06  2013-07  2013-08  2013-09  

i want take data interval 4, below record expected.

2013-01 2013-05 2013-09 2014-02 

and interval 2, below record expected

2013-01  2013-03  2013-05  2013-07  2013-09  

if using modulo % 2 start 2013-01 , jump 2, problem if range want start 2013-02, 02 self not showing on result. if clause month start 2 given interval such 2,4,6,8,10,12

select date_, sum(the_metric_you_want_to_aggregate) (   select 4*floor(    (date_format(subscribed_from, '%y%m') - 201301)    /4) date_,    the_metric_you_want_to_aggregate   subscription   operator = 'tim'   , subscribed_from between 20130101000000 , 201412315959 ) ilv group date_ 

(where 201301 year/month start of range selecting - assuming reference 4-month aggregation)

note enclosing column references in functions (...date_format(subscribed_from, '%y-%m-%d') between...) prevents use of indexes.