问题
What are the type of indexes in oracle? How to identify the index need to create?
回答1:
Oracle Database provides several indexing schemes that provide complementary performance functionality. These are:
- B-tree indexes: the default and the most common
- B-tree cluster indexes: defined specifically for cluster
- Hash cluster indexes: defined specifically for a hash cluster
- Global and local indexes: relate to partitioned tables and indexes
- Reverse key indexes: most useful for Oracle Real Application Clusters applications
- Bitmap indexes: compact; work best for columns with a small set of values
- Function-based indexes: contain the precomputed value of a function/expression Domain indexes: specific to an application or cartridge.
Source: http://docs.oracle.com/cd/B19306_01/server.102/b14231/indexes.htm
回答2:
There are a number of index types in Oracle, depending on what object you need to index:
For heap tables, there are b-tree indexes and bitmap indexes.
A b-tree index is suitable for most applications; bitmap indexes have their own advantages and disadvantages.
There are also specialised indexes for specific data types, using Oracle cartridges; e.g. Oracle Text indexes, spatial indexes, and 3rd party indexes.
Furthermore, an index might be differentiated by other factors:
- an index on a partitioned table might be global or local
- an index might consist of one column, or multiple columns
- an index might be on a normal column, or on an expression (aka "function-based" index)
For more info, read the documentation.
An excellent place to find out more than you'll ever want to know about Oracle indexes is Richard Foote's blog.
来源：https://stackoverflow.com/questions/2460399/types-of-index-in-oracle