select 月份 , 类型(a) ,类型(b)
from
(
select distinct 月份 from table
) as months
left join
(
select 总数 as 类型(a) from table where 类型='a'
) as a
on a.月份 = months.月份
left join
(
select 总数 as 类型(b) from table where 类型='6'
) as b
on b.月分 = months.月份