摘要：
基础语法：not in的写法中，内外表都要全表扫描select count * from test where object_name not in (select object_name from test2);not exists的写法中，内层表子查询可以走索引select count * from test2 t2 where not exists(select 1 from test t1 where t1.object_name=t2.object_name );（object_name上建有有索引）执行计划：再来看一下CBO模式下的情况：SQL> select * from 阅读全文
