select from A where A.id in (select id from B where **)

来源：学生作业帮编辑：作业帮分类：综合作业时间：2024/11/07 18:42:55

select ** from A where A.id in (select id from B where ****) 在以下哪种情况,select ** from A where
select ** from A where A.id in (select id from B where ****) 在以下哪种情况,此语句执行的速度快：（1）A表的记录数远多于B表的记录数；（2）A表的记录数远小于B表的记录数
当B表拥有很好的索引,不考虑两个表之间的连接速度,上面哪种情况,语句的执行的速度快

相对来说第一种情况快,sql查询的顺序是先查where 后面的结果,那么如果B表数据少,当然速度相对要快于数据多的情况.实际情况用内连接速度会快得多.

select ** from A where A.id in (select id from B where ****) delete from A where a_id in (select id from B where b_id in select id,name from student where id in ( select id from sco sql 中 select * from A left join B on A.id=B.id where A.id=?如 select distinct A.* from A,B where A.id = B.g_id and A.fwzid select * into b from a where 11 sql如何取交集有这样两条sql语句select distinct id from a where id='123'se mysql select * from lsdl_user where id in (1,2,3,4,5)中in()最多 $id="select id from account where name='".$_SESSION['login'] $query = mysql_query( select * from 表名 where id='$_GET[id]' SQL语句理解 select * from B where (select count(1) as num from A select top 10 * from (select top 40 * from a order by id asc