with t as (
select 销售年, 销售月, sum(金额) 月金额 from sales group by 销售年, 销售月
)
select 销售年, min(月金额), max(月金额) from t group by 销售年;

------解决方案--------------------

SQL code
with t as (
select 销售年, min(销售月) 最小月份, max(销售月) 最大月份 from sales group by 销售年
)
select t.销售年, 
(select sum(金额) from sales where sales.销售年=t.销售年 and sales.销售月=t.最小月份) 最小月份的金额,
(select sum(金额) from sales where sales.销售年=t.销售年 and sales.销售月=t.最大月份) 最大月份的金额 from t;