SQL Server enables you to create indexes on your tables and views to retrieve data more quickly and efficiently. Indexes can be clustered or non-clustered. Clustered indexes sort and store the data rows in the table or view based on their keys. There can only be one clustered index per table, because the data rows themselves can only be sorted in one order. Non-clustered indexes have a structure separate from the data rows. They are stored as B-trees (balanced trees) that consist of index keys and pointers to the data rows. Non-clustered indexes can be created on both tables and views.
Creating Clustered and Non-Clustered Indexes in SQL Server
What are Clustered and Non-Clustered Indexes?
Clustered and non-clustered indexes are both ways of organizing data in a SQL Server database. A clustered index is a way of sorting and storing data in a table so that it is physically stored in sorted order. A non-clustered index is a way of creating an index on a column or columns in a table that is not physically stored in sorted order.
How to create Clustered Indexes in SQL Server
Creating a clustered index on a SQL Server table can be done via the CREATE INDEX statement. This statement allows for the specification of the index name, the table name, and the column or columns to be included in the index. In the case of a clustered index, the data in the index will be sorted and physically stored in the order of the index columns. Clustered indexes can be created on bothHeap and Clustered tables.
The following is an example of how to create a clustered index on the “Customer” table, using the “LastName” and “FirstName” columns:
CREATE INDEX CustomerClusteredIndex
ON Customer (LastName, FirstName)
This example would create a clustered index on the Customer table, using the LastName and FirstName columns as the index keys. The data in the index would be sorted and stored in the order of those columns.
How to create Non-Clustered Indexes in SQL Server
To create a non-clustered index in SQL Server, you will need to use the CREATE INDEX statement. This statement allows you to specify the name of the index, the name of the table to index, and the columns to index.
You can use the following syntax to create a non-clustered index:
CREATE INDEX index_name
ON table_name (column1, column2, …)
Indexing is an important part of database performance tuning. By creating indexes on frequently accessed columns, you can improve the performance of your database queries. Indexes are especially important for columns that are used in joins or where conditions.
There are many different reasons why you might want to create a clustered index on a SQL Server table. In general, a clustered index will improve the performance of queries that access a small number of rows from the table. Creating a clustered index can also help to improve the performance of insert and update operations on the table.
Non-clustered indexes, on the other hand, can be used to improve the performance of queries that access a large number of rows from the table. Non-clustered indexes can also be used to improve the performance of insert and update operations on the table, but to a lesser extent than clustered indexes.
When deciding whether to create a clustered index or a non-clustered index on a SQL Server table, you will need to consider the trade-offs between the two. In general, clustered indexes are more efficient than non-clustered indexes, but they can take up more space on the disk. Non-clustered indexes are less efficient than clustered indexes, but they take up less space on the disk.
If you are not sure whether to create a clustered index or a non-clustered index on a SQL Server table, you can use the Database Engine Tuning Advisor to help you make the decision.