here i can such example

create table estr

(

custo int,

product varchar(20),

val int,

billed_date datetime

)

insert into estr(custo,product,billed_date,value) values('10','Milk','2013-04-11','2000')

insert into estr(custo,product,billed_date,value) values('10','Milk','2013-04-21','500')

insert into estr(custo,product,billed_date,value) values('10','Milk','2013-05-05','100')

insert into estr(custo,product,billed_date,value) values('10','Milk','2013-05-11','2000')

insert into estr(custo,product,billed_date,value) values('10','fruits','2013-05-11','500')

insert into estr(custo,product,billed_date,value) values('30','fruits','2013-04-11','2000')

insert into estr(custo,product,billed_date,value) values('30','fruits','2013-05-11','1000')

My expecting output

custo product value no.of.mon(bil_months)

10 milk 4600 2

10 fruits 500 1

30 fruits 3000 2

above example custo=10 milk has billed various date of april,may but when i count the month ll show only 2

how to do that?