Each key appears only once in the index - Oracle Clusters

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• Nirja Shah   -Posted on 01 Oct 15
  - You alter cluster indexes exactly as you do other indexes.
  
  - When estimating the size of cluster indexes, remember that the index is on each cluster key, not the actual rows. Therefore, each key appears only once in the index.
  
  - Indexes are optional structures associated with tables and clusters that allow SQL statements to execute more quickly against a table.
  
  - Just as the index in this manual helps you locate information faster than if there were no index, an Oracle Database index provides a faster access path to table data.
  
  - You can use indexes without rewriting any queries.
  
  - Your results are the same, but you see them more quickly.
  
  - Oracle Database provides several indexing schemes that provide complementary performance functionality.
  
  - Indexes are logically and physically independent of the data in the associated table. Being independent structures, they require storage space.
  
  - You can create or drop an index without affecting the base tables, database applications, or other indexes.
  
  - The database automatically maintains indexes when you insert, update, and delete rows of the associated table.
  
  - If you drop an index, all applications continue to work. However, access to previously indexed data might be slower.

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