Types Of Indexes In Sql Server 1

An index in SQL Server is a structural element that can be on disk or in memory that is connected to a table or view. Its main purpose is to quickly identify particular sets or rows in a table or view. Indexes improve the database engine’s ability to retrieve data more quickly by functioning as individual lookup tables. This article discusses the different types of indexes in SQL Server, providing an in-depth look of their distinctive characteristics and how they are essential to improving overall database performance.

Types of SQL Server Indexes:

There are various types of indexes in SQL Server. They are:

Clustered Index:

In SQL Server, a clustered index, falling under the category of types of indexes in SQL Server, organizes the index key in a B-tree structure, storing it alongside the actual table data in each leaf node. This design distinguishes it from a heap table, providing efficiency by avoiding an additional lookup when querying based on index key values, ultimately enhancing query performance. This advantage is particularly pronounced when the index key columns are utilized in the WHERE clause. Furthermore, the clustered index simplifies data retrieval by obviating the need for sorting when the ORDER BY clause is based on index key values. It’s important to note that a table can only have one clustered index defined on it.

Non-Clustered Index:

A nonclustered index can be applied to any table or view, regardless of whether it has a clustered index or is a heap. The nonclustered key value and a row locator are contained in each index row in this kind of index. When a key value is entered, this locator points to the data row in the heap or clustered index that matches it. The index rows are ordered by key values, but unless a clustered index is created on the table, the actual data rows are not arranged in any particular order. This indexing flexibility enables efficient data retrieval based on non-clustered key values in a variety of table structures.

Column store Index 

A column store index is a type of non-clustered index that is designed specifically for data indexing and has a distinct storage format. It can be built in either clustered or non-clustered form. With the ability to boost query performance by up to 100 times, column store indexes are perfect for large-scale data warehousing, particularly for fact tables. Furthermore, they offer data compression options, which can save up to ten times the amount of storage space, with compression efficacy depending on the selectivity of the column.

Hash Index

A hash index, falling under the umbrella of types of indexes in SQL Server, operates based on hash functions. Within the index structure, slots are composed of either arrays of N buckets or pointers to buckets, each intended to accommodate a single row. The hash function, denoted as F(K, N), determines the number of buckets (N) and associates the key (K) with the corresponding bucket in the hash index. Interestingly, each bucket utilizes eight bytes to store the memory address of the linked list with matching elements. This approach optimizes data retrieval in alignment with the hash function, ensuring swift and efficient access to specific index components.

Unique Index

In SQL Server, a unique index plays a crucial role in preserving data integrity by preventing the occurrence of duplicate entries in specified columns. This assurance of uniqueness holds true when the index key involves a single column, ensuring that each value is distinct. For a unique index involving multiple columns, every conceivable combination of values must be unique. Notably, both types of indexes in SQL Server—clustered and non-clustered—can be characterized as unique due to the distinctive properties of their index keys. This unique attribute of the index key serves to maintain the integrity of information in the designated columns and, consequently, ensures the uniqueness of the corresponding table rows.

Filtered Index

A Filtered index is a type of index in SQL server that was first introduced in SQL Server 2008 with the goal of enhancing query performance for particular subsets of rows. It indexes only a specific section of the table using a filter predicate, resulting in a lower index size and saving disk space. Performance is further improved by the addition of precise filtered statistics, which offer the best execution plans at the lowest possible maintenance costs. This focused technique offers efficiency advantages in query execution while saving storage resources, and it is especially useful when fetching well-defined portions of data from a table.


In conclusion, SQL Server provides a variety of index types to improve database performance and accelerate query processing. To grasp these Types of indexes in SQL Server, preserve database integrity, and achieve peak performance, you must receive SQL Server training in Chennai. Choosing the right kind of index is essential to maintaining database integrity and achieving exceptional performance.