在SQL中获取类别百分比的最有效方法是什么

假设我有一张这样的桌子-

with temp as 
(
select "a" as product, 100 as sales union all
select "b" as product, 200 as sales union all
select "c" as product, 300 as sales 

)

-- Query 1
with temp as 
(
select "a" as product, 100 as sales union all
select "b" as product, 200 as sales union all
select "c" as product, 300 as sales 

)

select *,
sales * 100 / sum(sales) over ()  as percentage_sales
from temp t

或者

-- Query 2
with temp as 

(
select "a" as product, 100 as sales union all
select "b" as product, 200 as sales union all
select "c" as product, 300 as sales 

)

, total as 
(
select sum(sales) grand_total from temp 
)

select product, sales, 
sales * 100 / t.grand_total as percentage_sales
from temp, total t

哪一个查询更高效和优化?它是基于我们使用的SQL引擎吗?或者这里有一个总的经验法则吗?

我试图从一般的角度来理解它,而不是从任何DBMS供应商的角度来理解它。