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Difference Between Clustered And Non-Clustered Index

Table of Contents

  1. What is an Index?
  2. A clustered index: What is it?
  3. Clustered Index Characteristic
  4. Non-clustered index: What is it?
  5. Non-clustered Indexes’ Characteristics
  6. Clustered versus non-clustered index

Indexes are crucial to the operation of SQL Server. The index helps improve the overall performance and timeliness of data retrieval. Using an example because understanding the real meaning of indexes. The included index makes it easy to find a chapter and page number in the textbook. An index also facilitates fast, simple, and efficient access in SQL.

Index stores the keys to enable SQL Server to rapidly and effectively access the rows corresponding to the key values. The index is often created automatically as the primary key, and unique constraints are indicated in the table.

If the table has a unique key and a unique constraint declared, an index is created right away. Indexes go into one of two categories: clustered or non-clustered. Compare and contrast the features of clustered & non-clustered indexes.

What is an Index?

An index is a key created from one or maybe more database columns that speed up the retrieval of data from a table or view. Thanks to this key, databases like Oracle,  MySQL, SQL Server, etc. may more quickly and simply retrieve the row linked with the key values.

Indexes are in two varieties:

  • Combined Index
  • Index, Non-Clustered

A clustered index: What is it?

The table’s data rows are organised to use a clustered index structure and sorted as per their key values. There is a single-clustered index for every table in the database.

There can only be a clustered index per table as a result. Using an RDBMS’s main key, you may frequently create a clustered index based on a particular column.

The only table that will be sorted whenever clustered indexing is utilised is that one. In a table where the primary key is present, just a clustered index may be created. Also, a clustered index, as well as a dictionary, have the material ordered alphabetically.

Instead of direct data, a clustered index only stores a block pointer.

Clustered Index Characteristic

  • Sorted and default data storage
  • Use a single column or several columns to create an index.
  • aids in the pooled storage of data and index.
  • Fragmentation\sOperations
  • Index seeks and clustered index scan
  • Key Search

Non-clustered index: What is it?

The data and indexes are stored separately in a non-clustered index. The index includes indices to the source of that data. A single table may have many non-clustered indexes due to the fact that non-clustered indexes maintain their indexes in numerous places.

For instance, a book may have more than one index, the first of which lists the book’s contents in terms of units and the second of which lists the terms in alphabetical order.

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Non-clustered Indexes' Characteristics

  • Merely save important values
  • Pointers to Heap/Clustered Index rows
  • Allows for secondary data access and a data bridge for index search and scan operations.
  • You may build a non-clustered index for a view or a table.
  • A row location and the non-clustered key value are stored in each index row of the non-clustered index.

Clustered versus non-clustered index

CLUSTERED INDEXNON-CLUSTERED INDEX
Faster is a clustered index.Slower is a non-clustered index.
Less memory is required for operation on the clustered index.For operations, a non-Clustered index needs more memory.
The index serves as the primary data in a clustered index.The copy of the data is the index in a non-clustered index.
There can only be one clustered index per table.Multiple Non Clustered indexes may exist for a given table.
Clustered index store references to block, not data.There is no intrinsic capacity for a non-Clustered index to hold information on a disc.
Indexes store block pointers rather than data?A non-clustered index keeps a worth & a pointer to the row that contains the data.
Leaf nodes are the actual data in a clustered index.In the Non-Clustered index, leaf nodes only contain included columns rather than the data itself.
The order of the data in a table is determined by the clustered key in a clustered index.The index key determines the data’s order in this non-clustered index.
Table entries are physically rearranged to fit the index in a clustered index, a form of an index.A this index is a special type of index in which the logical order of the index does not match the stored physical order of the rows on the disk.
The size of a clustered index is big.The size of this index is comparatively smaller.
By default, the table’s primary keys are clustered indexes.The composite key acts as a non-clustered index when combined with specific table restrictions.