急！！在线等

[shrek11]

优化数据库语句：
select * from eosoperator where operatorid in(select studentid from student where classid in(select classid from class where ishistoryclass=0))
在线等啊

[中国风]

用取真的方法测测:
select
*
from
eosoperator
where
exists(select 1 from class where ishistoryclass=0 and
exists(select 1 from student where classid=class.classid and student=eosoperator.operatorid) )

[中国风]

select   
	*   
from   
	eosoperator   
where  
	exists(select 1 from student where  student=eosoperator.operatorid 
	exists(select 1 from class where ishistoryclass=0 and classid=student.classid))

[dawugui]

试试

select a.*
from eosoperator a, student b,classwhere c
where a.operatorid = b.studentid and b.classid = c.classid and c.ishistoryclass=0

[xiangyu120]

select a.* from eosoperator a,student b,class c where a.operatorid=b.studentid and b.clssid=c.callssid and c.ishistoryclass=0

[toddzst]

就是，觉得LS的2位方法就可以，为什么非用子查询

[pt1314917]

select a.* from  eosoperator a,student b,class c where a.operatorid=b.studentid and b.classid=c.classid 
and c.ishistoryclass=0

[OracleRoob]

用关联吧，效率高些

[dobear_0922]

楼上两位的方法会有重复记录

[OracleRoob]

select a.* 
from eosoperator a
	inner join student b on a.operatorid = b.studentid
	inner join classwhere c on b.classid = c.classid 
where c.ishistoryclass=0 

[dobear_0922]

回完贴发现是三位了，，，

[dobear_0922]

用大家的方法，如果eosoperator表有１条记录，最终可能会查出１０条来，，，

[OracleRoob]

--try

select a.* 
from eosoperator a
    inner join 
	(select studentid from student b inner join classwhere c on b.classid = c.classid where c.ishistoryclass=0 group by studentid) as t
	on a.operatorid = t.studentid

[dobear_0922]

select E.*   
from eosoperator E join 
(select distinct studentid 
	from student B join (select classid from class where ishistoryclass=0) C on B.classid=C.classid) T
on E.operatorid=T.studentid

[shrek11]

我马上测试一哈，
把结果给大家看看
谢谢你们拉

[GEPIN]

联机帮助上不是有写么：当子查询里有in or exists语句，使用JOIN语句，效率要高么？
况且效率高不高和你的数据量，索引结构都有关。