Index in SQL Server

-> An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. A table can have one of the following index configurations.

  • No indices
  •  A clustered index
  •  A clustered index and many non clustered indices
  • A non clustered index
  • Many non clustered indices

Clustered Index
-> is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

Non Clustered Index
-> is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages.Instead, the leaf nodes contain index rows.

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