问个sql语句，如何写效率高

一张表，其他地方从它这里取数据，一对多的关系，我要显示还剩多少没取。比如这样，效率高吗：sql1：
select a.id,a.quantity,b.bqty from test1 a
left join
(
select linkid ,sum(quantity) as bqty from test2 group by LinkID ) b on b.LinkID= a.ID


sql2：
select test1id,quantity ,sum(test2quan) from (
select a.id test1id ,a.quantity,b.quantity test2quan from test1 a inner join test2 b on b.LinkID=a.ID)t
group by test1id,quantity