Which are the different types of indexes in SQL?

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There are three types of Indexes in SQL:

  • Unique Index
  • Clustered Index
  • NonClustered Index
  • Bit-Map index
  • Normal index
  • Composite index
  • B-tree index
  • function based index

In SQL, there are primarily three types of indexes:

  1. Clustered Index:
    • Defines the order in which data is physically stored in a table.
    • The table can have only one clustered index.
    • Reorganizes the data rows in the table to match the order of the clustered index key.
  2. Non-Clustered Index:
    • Does not alter the physical order of the table and maintains a separate structure to store indexing information.
    • The table can have multiple non-clustered indexes.
    • Generally, non-clustered indexes provide faster retrieval of data based on the indexed columns.
  3. Unique Index:
    • Similar to a non-clustered index but enforces the uniqueness of values in the indexed columns.
    • No two rows can have the same indexed values in a unique index.

Other types of indexes may be supported in specific database management systems (DBMS), but these three are the fundamental and widely used types in SQL databases. Additionally, some databases support full-text indexes, spatial indexes, and other specialized index types based on their features and requirements.