webstorm做网站/搜索引擎优化概述

降序索引本质上是FBI，其具体定义可以通过 user_ind_expressions 或dba_ind_expressions 查询。那么同样的，降序索引只有在CBO下才能被使用。 Connected to Oracle9i Enterprise Edition Release 9。

2。0。4。

0 Connected as eygleSQL> create table t as select * from dba_users;Table createdSQL> create index idx_username_desc on t(username desc);Index createdSQL> select index_name,table_name,INDEX_TYPE from user_indexes where table_name=@#T@#;INDEX_NAME TABLE_NAME INDEX_TYPE------------------------------ ------------------------------ ---------------------------IDX_USERNAME_DESC T FUNCTION-BASED NORMALSQL> select column_name,column_position,descend from user_ind_columns2 where table_name=@#T@#;COLUMN_NAME COLUMN_POSITION DESCEND------------------------------ --------------- -------SYS_NC00013$ 1 DESCSQL> SQL> select * from user_ind_expressions where table_name=@#T@#;INDEX_NAME TABLE_NAME COLUMN_EXPRESSION COLUMN_POSITION------------------------------ ------------------------------ ------------------------------ ---------------IDX_USERNAME_DESC T "USERNAME" 1。

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