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In SQL Server, one of the powerful features available is Columnstore indexes. A Columnstore index is a technology for storing, retrieving and managing data by using a columnar data format, called a columnstore. This was introduced in SQL Server 2012 to speed up the performance of data warehouse queries. >From SQL Server 2014 onwards, Columnstore indexes are not just for reading operations, but also for transactional operations. This blog post will go through the basics of the SQL Server In-Memory Columnstore indexes, how to create them, and how to utilize them effectively.
What is a Columnstore index?
A Columnstore index can efficiently compress and scan large amounts of data. It’s best suited for data warehousing tables where queries often perform operations involving a full table or large range of rows to summarize data, run analytics, and generate reports. The structure of a Columnstore index allows SQL Server to process data more efficiently by reading and analysing column-based data, rather than traditional row-based data.
Creating a Columnstore Index
Let’s consider a test table named ‘Sales’ and we will create a non-clustered Columnstore index on it. The SQL code to accomplish this will look something like this:
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CREATE NONCLUSTERED COLUMNSTORE INDEX NCCI_Sales ON Sales (OrderID, OrderDate, Amount); |
This code creates a non-clustered Columnstore index with the name ‘NCCI_Sales’ on the Sales table, specifically on the OrderID, OrderDate, and Amount columns.
Querying a Table using Columnstore Index
When querying a table with a Columnstore index, SQL Server’s Query Optimizer typically selects the Columnstore index for the query execution plan, if it determines that the plan leads to a more efficient query performance. Here is an example of a simple SELECT statement.
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SELECT OrderDate, SUM(Amount) FROM Sales GROUP BY OrderDate; |
In this case, SQL Server will automatically use the ‘NCCI_Sales’ Columnstore index to execute the query, reading only the required columns’ data, reducing I/O and CPU utilization.
Conclusion
Understanding In-memory Columnstore indexes is vital for developers and database administrators who work with large volumes of data and need rapid data retrieval solutions. This feature can enhance the performance of data warehousing and analytic solutions by reducing the storage footprint and improving query performance.
Remember, practice makes perfect. So get onto your SQL Server and start writing queries, create some Columnstore indexes, and see the difference they make.