摘要： from http://oracle-base.com/articles/misc/virtual-indexes.phpThe process of tuning SQL statements often requires the testing of alternate indexing str... 阅读全文

摘要： 下面的两个SQL是等价的，但是一个执行N小时都执行不完，一个花了一分钟。执行计划显示第一个语句是由外面的即将被更新的表驱动内层，相对于是一个NEST LOOP，cost非常大。第二个语句是内层单独执行完后，与外面的筛选结果做一个HASH JOIN, cost降低了很多.UPDATE GPCOMP1.... 阅读全文

摘要： Virtual index can be created in oracle database which doesn't has any physical body and location. It can create with NOSEGMENT clause for testing purp... 阅读全文