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What is an index? - Indexes of SQL Server are similar to the indexes in books.
- They help SQL Server retrieve the data quicker.
- Indexes are of two types. Clustered indexes and non-clustered indexes.
- Rows in the table are stored in the order of the clustered index key.
- There can be only one clustered index per table.
- Non-clustered indexes have their own storage separate from the table data storage.
- Non-clustered indexes are stored as B-tree structures.
- Leaf level nodes having the index key and it's row locater
Disadvantages of the Indexes are
- Use of intexes slow down Data modification operations (such as INSERT, UPDATE, DELETE).
- Every time data changes in the table, all the indexes need to be updated.
- Indexes need disk space, the more indexes you have, more disk space is used
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