Categories
28°C, New York
Home SQL How to use ROW_NUMBER() In SQL

How to use ROW_NUMBER() In SQL

1. Using Subqueries

3. Using CROSS APPLY

This method uses the ROW_NUMBER() window function to assign a unique row number to each row in the EmployeeReviews table, partitioned by EmployeeID and ordered by ReviewDate.

The main query then filters the results to include only rows where the row number is 1, effectively selecting the first row for each employee.

WITH RankedReviews AS (
    SELECT
        r.EmployeeID,
        r.ReviewDate,
        r.Rating,
        ROW_NUMBER() OVER (PARTITION BY r.EmployeeID ORDER BY r.ReviewDate) AS RowNum
    FROM
        EmployeeReviews r
)
SELECT
    e.EmployeeID,
    e.Name,
    e.Salary,
    rr.ReviewDate,
    rr.Rating
FROM
    Employee e
    LEFT JOIN RankedReviews rr ON e.EmployeeID = rr.EmployeeID AND rr.RowNum = 1;

Output:

Explanation:

  • The ROW_NUMBER() function assigns a unique row number to each row in the EmployeeReviews table, partitioned by EmployeeID and ordered by ReviewDate. This ensures that the first row for each employee is assigned a row number of 1.
  • The main query then left joins the Employee table with the RankedReviews common table expression (CTE) on EmployeeID and RowNum = 1. This ensures that only the first row for each employee is included in the result.

How to Join to First Row in SQL Server

Joining the first row in SQL Server can be a common requirement in various scenarios, such as when we need to retrieve specific data associated with the first occurrence of a particular group or when you want to fetch additional details related to the first record in a result set.

In this article, We will learn about How to Join to first row in SQL Server by understanding various approaches along with the examples and so on.

Similar Reads

How to Join First Row in SQL Server?

When working with SQL Server, we may encounter situations where we need to join to the first row of a related table. This could be to retrieve the earliest record for each group or to extract initial data for further analysis. To solve this problem, we’ll explore three different approaches are as follows:...

1. Using Subqueries

This method uses a subquery to select the first row from the EmployeeReviews table for each employee. The subquery is joined to the Employee table using a LEFT JOIN to ensure that all employees are included in the result, even if they don’t have a corresponding row in the EmployeeReviews table.....

2. Using ROW_NUMBER()

This method uses the ROW_NUMBER() window function to assign a unique row number to each row in the EmployeeReviews table, partitioned by EmployeeID and ordered by ReviewDate....

3. Using CROSS APPLY

This method uses the CROSS APPLY operator to apply a table-valued function (in this case, a subquery) to each row from the Employee table....

CONCLUSION

Partitioning into first row of SQL Server can be implemented by different methods, including subqueries with ROW_NUMBER (), cross apply with TOP or Common Table Expressions (CTE). Different procedures will be good for various purposes and might be more appropriate depending on the particularities of your choosing and the difficulty of your information. As you learn these methods, you can appropriately apply them to your queries in order to easily get the necessary data from your SQL Server database....

Tags:
#SQL Server Query #Databases #SQL Server

1. Using Subqueries

3. Using CROSS APPLY