仅涵盖一个值的数据库索引
我有一个巨大的表（数百万条记录），其中几百到几千条由布尔字段标记（值 = 1 而不是 0）。
我只关心真实的记录（值 = 1）。有没有办法创建一个仅“索引”这些记录的索引？我应该使用什么样的指数？
select count(*)
from records
where boolean_field = 1
环境：Oracle 10g（但我也对其他dbms的评论感兴趣）
谢谢！
I have huge table (millions of records) in which a few hundreds to a few thousands are marked by a boolean field (value = 1 instead of 0).
I only care for records which are true (value = 1). Is there a way to create an index which only 'indexes' these records? What kind of indices should I use?
select count(*)
from records
where boolean_field = 1
Environment: Oracle 10g (but I'm also interested in comments about other dbms)
Thank you!
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如果您可以将“假”值设置为 null 而不是 0，那么您将获得您想要的结果。
否则，您可以创建一个基于函数的索引，如下所示：
这只会索引 1，但要让 Oracle 在查询中使用它，您的查询必须类似于：
If you could make your "false" value be null rather than 0, you would achieve the result you want.
Otherwise, you could create a function-based index like this:
That would only index the 1s, but for Oracle to use it in your queries your queries would have to be like:
这似乎是 Oracle 中位图索引的典型情况。
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_5010.htm#i2062403
This seems like a typical case for bitmap indexes in oracle.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_5010.htm#i2062403