17,377
社区成员
发帖
与我相关
我的任务
分享
...全文
请发表友善的回复…
发表回复
waxle 2004-08-10
- 打赏
- 举报
找本书看看吧，很容易的。
Tabalulu 2004-08-10
- 打赏
- 举报
说得很清楚了丫
myf7961 2004-08-10
- 打赏
- 举报
再回答回答我就给分了！！
beckhambobo 2004-08-08
- 打赏
- 举报
UNIQUE
Specify UNIQUE to indicate that the value of the column (or columns) upon which the index is based must be unique. If the index is local nonprefixed (see local_partitioned_index), then the index key must contain the partitioning key.
BITMAP
Specify BITMAP to indicate that index is to be created with a bitmap for each distinct key, rather than indexing each row separately. Bitmap indexes store the rowids associated with a key value as a bitmap. Each bit in the bitmap corresponds to a possible rowid, and if the bit is set, it means that the row with the corresponding rowid contains the key value. The internal representation of bitmaps is best suited for applications with low levels of concurrent transactions, such as data warehousing.
--------------------------------------------------------------------------------
Note:
Oracle does not index table rows in which all key columns are null except in the case of bitmap indexes. Therefore, if you want an index on all rows of a table, you must either specify NOT NULL constraints for the index key columns or create a bitmap index.
Specify UNIQUE to indicate that the value of the column (or columns) upon which the index is based must be unique. If the index is local nonprefixed (see local_partitioned_index), then the index key must contain the partitioning key.
BITMAP
Specify BITMAP to indicate that index is to be created with a bitmap for each distinct key, rather than indexing each row separately. Bitmap indexes store the rowids associated with a key value as a bitmap. Each bit in the bitmap corresponds to a possible rowid, and if the bit is set, it means that the row with the corresponding rowid contains the key value. The internal representation of bitmaps is best suited for applications with low levels of concurrent transactions, such as data warehousing.
--------------------------------------------------------------------------------
Note:
Oracle does not index table rows in which all key columns are null except in the case of bitmap indexes. Therefore, if you want an index on all rows of a table, you must either specify NOT NULL constraints for the index key columns or create a bitmap index.
tyrone98 2004-08-07
- 打赏
- 举报
unique 是指值不可重复的索引，是用B*树来保存的。
bitmap 一般用于值重复率很高的索引，如性别字段只有男、女两种选项。
bitmap 一般用于值重复率很高的索引，如性别字段只有男、女两种选项。
myf7961 2004-08-07
- 打赏
- 举报
回答呀，高手们！
