IN與EXISTS對SQL優化的影響

select * from v$version;

drop table emp purge;
drop table dept purge;
create table emp as select * from scott.emp;
create table dept as select * from scott.dept;
set timing on 
set linesize 1000
set autotrace traceonly explain

--這三種寫法代價一樣
select * from dept where deptno NOT IN ( select deptno from emp ) ;
select * from dept where not exists ( select deptno from emp where emp.deptno=dept.deptno) ;
select * from dept where deptno NOT IN ( select deptno from emp where deptno is not null) and deptno is not null;
 

在ORACLE11g中，IN才用的是anti演算法，EXISTS才用的也是anti演算法，所以代價一樣。

在ORACLE10g中，IN才用的是anti演算法，EXISTS才用的filter演算法，所以代價不一樣。