单独型操作

SQL> explain plan for select deptno,count(*) from emp where job='CLERK' and sal<1200 group by deptno;

 

 

SQL> select * from table(dbms_xplan.display);

 

 

0 SELECT STATEMENT

1  HASH GROUP BY

2     TABLE ACCESS FULL

 

2-filter("SAL" < 1200 AND "JOB"='CLERK'

 

 

 

create index EMP_JOB_I on emp(job); 创建索引后

SQL> explain plan for select deptno,count(*) from emp where job='CLERK' and sal<1200 group by deptno;

Explained.

SQL> select * from table(dbms_xplan.display);

 

 

0  SELECT STATEMENT

1     HASH GROUP BY

2       TABLE ACCESS BY INDEX ROWID

3             INDEX RANGE SCAN

 

 

2-filter("SAL"<1200)

3-access("JOB"='CLERK')