Introduction
The robust database management system SQL Server offers a variety of tools to alter data in different ways. The advanced window functions in SQL Server are one such collection of features. With the use of a window of rows and these functions, you may carry out intricate calculations and aggregates of data.
The advanced window functions in SQL Server will be discussed in this article with examples.
ROW_NUMBER() Function in SQL Server
The ROW_NUMBER() function assigns a unique sequential number to each row in the result set based on the specified order. It is often used to generate a unique identifier for each row.
Example
SELECT ROW_NUMBER() OVER (ORDER BY SalesAmount DESC) AS RowNum,
SalesPerson, SalesAmount
FROM dbo.SalesData;
RANK() Function in SQL Server
The RANK() function assigns a rank to each row based on the specified order. Rows with the same values are assigned the same rank, and the next rank is skipped.
Example
SELECT RANK() OVER (ORDER BY SalesAmount DESC) AS Rank,
SalesPerson, SalesAmount
FROM dbo.SalesData;
DENSE_RANK() Function in SQL Server
The DENSE_RANK() function is similar to the RANK() function, but it does not skip any ranks. Rows with the same values are assigned the same rank, and the next rank is not skipped.
Example
SELECT DENSE_RANK() OVER (ORDER BY SalesAmount DESC) AS DenseRank,
SalesPerson, SalesAmount
FROM dbo.SalesData;
NTILE() Function in SQL Server
The NTILE() function divides the result set into a specified number of groups and assigns a group number to each row based on the specified order.
Example
SELECT NTILE(4) OVER (ORDER BY SalesAmount DESC) AS Quartile,
SalesPerson, SalesAmount
FROM dbo.SalesData;
LAG() Function in SQL Server
The LAG() function returns the value from the previous row in the result set based on the specified order. You can also specify a default value to return if there is no previous row.
Example
SELECT LAG(SalesAmount, 1, 0) OVER (ORDER BY SalesPerson) AS PrevSalesAmount,
SalesPerson, SalesAmount
FROM dbo.SalesData;
LEAD() Function in SQL Server
The LEAD() function returns the value from the next row in the result set based on the specified order. You can also specify a default value to return if there is no next row.
Example
SELECT LEAD(SalesAmount, 1, 0) OVER (ORDER BY SalesPerson) AS NextSalesAmount,
SalesPerson, SalesAmount
FROM dbo.SalesData;
Conclusion
SQL Server’s advanced window procedures offer a robust toolkit for carrying out intricate computations and aggregations of data using a window of rows. The numerous advanced window functions available in SQL Server include many more than the ones we’ve covered in this article. You can advance your SQL knowledge and become a more proficient data analyst or developer by understanding these functions.