Order By will first use your memory which is defined in sort_area_size , if the sort_area_size is not able to allocate the enough memory , Oracle will allocate disk space in temporary tablespace to perform sort , which is considered to be very slow.SO what to do is enlarge the sort area size , so all the sorting is performed in memory only .
如是前者就有问题了, 在非 ORDER BY 字段建索引会提高性能?
问题依然!
我现在关心的是: 在非 ORDER BY 字段建索引会提高性能?