7 SQL优化技术

7.1 改变访问结构

7.2 修改SQL语句

SELECT deptno
  FROM dept
WHERE deptno NOT IN (SELECT deptno FROM emp);

SELECT deptno
  FROM dept
WHERE NOT EXISTS
          (SELECT 1
             FROM emp
            WHERE emp.deptno = dept.deptno);

 
SELECT deptno FROM dept
MINUS
SELECT deptno FROM emp;

SELECT dept.deptno
  FROM dept, emp
WHERE dept.deptno = emp.deptno(+) AND emp.deptno IS NULL;

7.3 提示hint
      提示的分类
     

初始化参数提示	all_rows,cursor_sharing_extract,dynamic_sampling,first_rows,gather_plan_statistics…
查询转化提示	(no_)eliminate_join,no_expand,(no_)merge…
访问路径提示	full,index,index_ffs…
连接提示	leading,ordered…
并行处理提示	parallel…
其他提示	(no_)append,(no_)cache…

7.4 改变执行环境

7.5 SQL概要

7.6 存储提纲

7.7 SQL计划基线

7.8 小结