Difference Between Clustered and Non-Clustered Index
Difference Between Clustered and Non-Clustered Index
Difference Between Clustered and Non-Clustered Index
index
By Richard Peterson Updated June 3, 2023
A cluster index is a type of index that sorts the data rows in the table on
their key values, whereas the Non-clustered index stores the data at one
location and indices at another location.
Clustered index stores data pages in the leaf nodes of the index, while the
Non-clustered index method never stores data pages in the leaf nodes of
the index.
The cluster index doesn’t require additional disk space, whereas the Non-
clustered index requires additional disk space.
Cluster index offers faster data access, on the other hand, the Non-clustered
index is slower.
What is an Index?
An Index is a key built from one or more columns in the database that speeds up
fetching rows from the table or view. This key helps a Database like Oracle, SQL
Server, MySQL, etc. to find the row associated with key values quickly.
Two types of Indexes are:
Clustered Index
Non-Clustered Index
A clustered index defines the order in which data is stored in the table which can
be sorted in only one way. So, there can be an only a single clustered index for
every table. In an RDBMS, usually, the primary key allows you to create a
clustered index based on that specific column.
For example, a book can have more than one index, one at the beginning which
displays the contents of a book unit wise while the second index shows the
index of terms in alphabetical order.
A non-clustering index is defined in the non-ordering field of the table. This type
of indexing method helps you to improve the performance of queries that use
keys which are not assigned as a primary key. A non-clustered index allows you
to add a unique key for a table.
You can sort the records and A non-clustered index helps you
store clustered index to creates a logical order for
Use for
physically in memory as per data rows and uses pointers for
the order. physical data files.
Clustered indexes are an ideal option for range or group by with max, min,
count type queries
In this type of index, a search can go straight to a specific point in data so
that you can keep reading sequentially from there.
Clustered index method uses location mechanism to locate index entry at
the start of a range.
It is an effective method for range searches when a range of search key
values is requested.
Helps you to minimize page transfers and maximize the cache hits.
Advantages of Non-clustered index
Pros of using non-clustered index are:
A non-clustered index helps you to stores data in a logical order but does
not allow to sort data rows physically.
Lookup process on non-clustered index becomes costly.
Every time the clustering key is updated, a corresponding update is
required on the non-clustered index as it stores the clustering key.
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