clustered index - Wikitechy

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What is Indexing in Database ?

Indexing is the One of the ways that will optimize the database searching and accessing is having indexes on the columns that access the data in a database table.
An index object is created in database with the column/columns value that are mentioned while creating the index.
The value in the index holds the row id of the physical data location in the database which helps for fast data retrieval of the corresponding rows.

What is Indexing Database

Types Of Index

Clustered indexes define the physical sorting of a database table’s rows in the storage media. For this reason, each database table may have only one clustered index.
Non-clustered indexes are created outside of the database table and contain a sorted list of references to the table itself.

Cluster & Non Clustered Index

Cluster & Non Clustered Index

Advantages of Indexes

Indexes their use in queries usually results in much better performance.
Make it possible to quickly retrieve (fetch) data.
They can be used for sorting. A post-fetch-sort operation can be eliminated.
Unique indexes guarantee uniquely identifiable records in the database.

Disadvantages of Indexes

They decrease performance on inserts, updates, and deletes.
It will take up space (this increases with the number of fields used and the length of the fields).
Some databases will monocase values in fields that are indexed.

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Difference between Clustered and Non-clustered index ?

Clustered Index	Non-clustered Index
Clustered index will be created by default when you create primary key on a column. So we can create one clustered index per table.	Non clustered index will be created automatically when you create unique key on a column. A table can have no.of unique keys, so we can create no.of non-clustered indexes per table.
The Leaf Level of a clustered index is the actual data page.	The Leaf Level of a non-clustered index does not consist of the actual data page.
Only one clustered index can be created.	Many non clustered index(Numbers depends on the database software) can be created.

Cluster and Non Cluster Index

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