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Index

An index is a method of allowing faster retrieval of records. An index creates an entry for each value that appears in the indexed columns. By default, Oracle creates B-tree indexes.

Types of indexes

  1. B Tree
    General purpose indexes in oracle, they are default indexes in oracle. B tree index can have at most 32 columns.
  2. Bitmap
    Bitmap indexes are ideal in cases where low number of distict values. It is ideal for DSS systems where more read happens. It can also have at most 32 columns. But it is used for less number of columns.
  3. Hash
    Indexes created on hash cluster
  4. Index-organized table
    An index orgnized table is a type of table that stores data in B Tree index structure that is logically sorted in primary key.
  5. Reverse key
    reverse key index works only on exact match. It does not use range scan.
  6. Function based key
    Indexes created on function based column
  7. Partitioned (Local and Global)
    Breaking indexes into pieces.
  8. Bitmap join indexes

For details about B-Tree and Bit-Map indexes, please refer the link B-Tree/Bit-Map

Oracle documentation on index Index

Index and index orgnized table IOT