SELECT Top N Rows For Each Group in SQL Server

The ROW_NUMBER() window function in SQL Server is used to assign unique row numbers to the rows within a partition. Combined with the PARTITION BY clause, it becomes an effective way to rank and filter results within each group.

Steps:

1. Apply the ROW_NUMBER() function to your result set, and specify the PARTITION BY clause to define the grouping based on a specific column.
2. Create a Common Table Expression (CTE) to organize the query and simplify the final selection of rows.
3. Filter the results from the CTE based on the row number and select only the top N rows within each group.

Syntax:

WITH CTE AS (
  SELECT
    <group_column>,
    <value_column>,
    ROW_NUMBER() OVER (PARTITION BY <group_column> ORDER BY <value_column> DESC) AS row_num
  FROM
    <Table>
)
SELECT * FROM CTE WHERE row_num <= N;

• <group_column>: This represents the column by which you want to group your data. In the context of the example, it could be the Region column as we are grouping by region.
• <value_column>: This represents the column based on which you want to order the data within each group. In the example, it’s Revenue, as we want to rank salespeople within each region by their revenue.
• <Table>: This represents the table from which you are selecting data. In the example, it’s the Sales table.

SQL Server’s ROW_Number() window function is often used to get the top number of rows in a group. In this article, we’ll look at how to get the top N Row Counts in SQL Server using this function. We’ll provide step-by-step instructions, syntax examples, and examples to help you get the results you need.

ROW_Number() is used in conjunction with PARTITION BY to rank and filter within a group. By using this function, you can get the top n Row Counts based on a specific column, improving the analytical performance of your SQL query.