第一个时使用聚合函数sum

SELECT g.id,g.name,g.weight,t.total
FROM goods g,(
    select goods_id,sum(count) total
    from trans 
    group by goods_id
) t
WHERE g.id=t.goods_id
and t.total>20
and g.weight<50;

第二个使用窗口函数sum

with t as(
select goods_id,
     sum(count) over (partition by goods_id) total
from trans
)
SELECT distinct g.id,g.name,g.weight,t.total
FROM goods g,t
WHERE  g.id=t.goods_id
and t.total>20
and g.weight<50;