SQL Server Columnstore indexes are a type of index that stores data in a column-based format rather than a row-based format. This allows for faster querying of large data sets, particularly for data warehousing and business intelligence workloads.

Columnstore indexes can be created on both clustered and nonclustered tables, and can include multiple columns. They use a compressed, read-only format, which makes them highly efficient for data warehousing and analytics queries.

Additionally, SQL Server can use a technology called batch mode processing to further improve query performance on columnstore indexes, by processing large numbers of rows at once.

Example

Here's an example of creating a Columnstore index in SQL Server:

Suppose you have a table called Sales with the following columns: SaleDate (date), Product (nvarchar(50)), Category (nvarchar(50)), Region (nvarchar(50)), Amount (decimal(18,2)).

CREATE TABLE Sales(
SaleDate DATE,
Product NVARCHAR(100),
Category NVARCHAR(100),
Region NVARCHAR(100),
Amount DECIMAL(18,2)
);

To create a Clustered Columnstore index on the Sales table, you can use the following SQL query:

CREATE CLUSTERED COLUMNSTORE INDEX CSI_Sales
ON Sales;

This will create a new Columnstore index called CSI_Sales on the Sales table. The Columnstore index will compress the data and store it in a columnar format, making it faster to query large amounts of data.

You can also create a Nonclustered Columnstore index on a table by specifying the NONCLUSTERED keyword:

CREATE NONCLUSTERED COLUMNSTORE INDEX NCSI_Sales
ON Sales (Product, Category, Region);

This will create a Nonclustered Columnstore index called NCSI_Sales on the Sales table, with the specified columns as the key columns. This index will also compress the data and store it in a columnar format, but it will be separate from the table data and not affect the table's physical order.