ORACLE SQL性能优化系列 (九)[6]

     这里, oracle只用到了dept_no索引. 执行路径如下:

     table access by rowid on emp

          index range scan on dept_idx

译者按:

我们来试一下以下这种情况:

sql> select index_name, uniqueness from user_indexes where table_name = 'emp';

index_name                     uniquenes

------------------------------ ---------

empno                          unique

emptype                        nonunique

sql> select * from emp where empno >= 2 and emp_type = 'a' ;