创建两张表先单独插入两条数据
然后批量插入部门号为10,20,30,40的数据各10499099条
然后dept表也插些干扰数据
测试语句
开始验证in和exists和join
先比较个占比多的部门，再比较占比少的
1、 in 占比多
select count(*) from scott.EMP_TEST e where e.deptno in (select d.deptno from scott.DEPT_TEST d where d.dname='SALES') ;
跟真实执行计划基本一样，所以之后的都用autotrace来看
2.exists 占比多
select count(*) from scott.EMP_TEST e where exists (select d.deptno from scott.DEPT_TEST d where d.dname='SALES' and e.deptno=d.deptno) ;
3.join 占比多
select count(*) from scott.EMP_TEST e inner join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname='SALES' ;
http://4.in 占比少
select count(*) from scott.EMP_TEST e where e.deptno in (select d.deptno from scott.DEPT_TEST d where d.dname='TEST') ;
5.exists 占比少
select count(*) from scott.EMP_TEST e where exists (select d.deptno from scott.DEPT_TEST d where d.dname='TEST' and e.deptno=d.deptno) ;
6.join 占比少
select count(*) from scott.EMP_TEST e inner join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname='TEST' ;
7.not in 占比多
select count(*) from scott.EMP_TEST e where e.deptno not in (select d.deptno from scott.DEPT_TEST d where d.dname<>'SALES') ;
8.not exists 占比多
select count(*) from scott.EMP_TEST e where not exists (select d.deptno from scott.DEPT_TEST d where d.dname<>'SALES' and e.deptno=d.deptno) ;
9.join 占比多
select count(*) from scott.EMP_TEST e left join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname<>'SALES' where d.deptno is null ;
10.not in 占比少
select count(*) from scott.EMP_TEST e where e.deptno not in (select d.deptno from scott.DEPT_TEST d where d.dname<>'TEST') ;
11. not exists 占比少
select count(*) from scott.EMP_TEST e where not exists (select d.deptno from scott.DEPT_TEST d where d.dname<>'TEST' and e.deptno=d.deptno) ;
12. join 占比少
select count(*) from scott.EMP_TEST e left join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname<>'TEST' where d.deptno is null ;
下面创建两个简单索引来测试下
1、 in 占比多
select count(*) from scott.EMP_TEST e where e.deptno in (select d.deptno from scott.DEPT_TEST d where d.dname='SALES') ;
分析不走索引的原因是因为统计信息不全，收集下统计信息
2.exists 占比多
select count(*) from scott.EMP_TEST e where exists (select d.deptno from scott.DEPT_TEST d where d.dname='SALES' and e.deptno=d.deptno) ;
3.join 占比多
select count(*) from scott.EMP_TEST e inner join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname='SALES' ;
http://4.in 占比少
select count(*) from scott.EMP_TEST e where e.deptno in (select d.deptno from scott.DEPT_TEST d where d.dname='TEST') ;
5.exists 占比少
select count(*) from scott.EMP_TEST e where exists (select d.deptno from scott.DEPT_TEST d where d.dname='TEST' and e.deptno=d.deptno) ;
6.join 占比少
select count(*) from scott.EMP_TEST e inner join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname='TEST' ;
7.not in 占比多
select count(*) from scott.EMP_TEST e where e.deptno not in (select d.deptno from scott.DEPT_TEST d where d.dname<>'SALES') ;
8.not exists 占比多
select count(*) from scott.EMP_TEST e where not exists (select d.deptno from scott.DEPT_TEST d where d.dname<>'SALES' and e.deptno=d.deptno) ;
9.join 占比多
select count(*) from scott.EMP_TEST e left join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname<>'SALES' where d.deptno is null ;
10.not in 占比少
select count(*) from scott.EMP_TEST e where e.deptno not in (select d.deptno from scott.DEPT_TEST d where d.dname<>'TEST') ;
11. not exists 占比少
select count(*) from scott.EMP_TEST e where not exists (select d.deptno from scott.DEPT_TEST d where d.dname<>'TEST' and e.deptno=d.deptno) ;
12. join 占比少
select count(*) from scott.EMP_TEST e left join scott.DEPT_TEST d on e.deptno=d.deptno and d.dname<>'TEST' where d.deptno is null ;
在简单比较下时间
可以看出在相同条件下，执行计划是相同的，时间消耗也是一样的
因为有朋友说not exists的子查询会走索引not in索引失效，所以not exists会快，所以为了说服他又做了点补充
并没有什么差别。而且not in和not exists都会使索引失效，但是不影响子查询的索引使用！！！！所以直接说谁比谁快的都是不负责任的说法，还是要具体情况具体分析。分情况使用。那些说not exists比not in快的，这种情况很多，因为不同的原因造成他们的sql的执行计划不同了，所以效率也不同了
抛开执行计划和实际情景，不考虑数据情况，数据量、索引情况甚至统计信息等这些因素，直接说哪一种比较快都是不靠谱的
