杂谈sql

oracle中关于一些sql的问题

select t1.* from Tplatforminfo t1  where t1.id not in(select t2.platformid from Ttrsplatformtag t2);

select t1.* from Tplatforminfo t1  where not exists(select t2.platformid from Ttrsplatformtag t2 where t2.platformid=t1.id);

not in 与 not exists的区别：
当t1表数量大；t2表的数量少时；not exists效率高
当t1表数量少；t2表的数量多时；not in效率高