What are indexes ?

Question

What are indexes ?

Accepted Answer

Indexes are data structures that improve the speed of data retrieval operations on a database table.

Indexes are created on one or more columns of a table.
They allow the database to quickly find the rows that match a search condition.
Indexes can be unique or non-unique.
Unique indexes ensure that no two rows have the same value for the indexed columns.
Non-unique indexes allow duplicate values for the indexed columns.
Indexes can be created using different algorithms, such as B-tree, hash, or bitmap.
B-tree indexes are the most common type of index and are used for range queries.
Hash indexes are used for equality queries.
Bitmap indexes are used for low-cardinality columns.
Indexes can also be clustered or non-clustered.
Clustered indexes determine the physical order of data in a table.
Non-clustered indexes are separate data structures that point to the data in a table.

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