Understanding Rownum in SQL Server

Hello Dev, welcome to this article that aims to provide a comprehensive understanding of Rownum in SQL Server. In this article, we will cover the basics of Rownum, how to use it, and how it can help you in optimizing your database queries. Let’s get started.

What is Rownum in SQL Server?

Rownum is a pseudo column in SQL Server that assigns a unique number to each row returned by a query. It helps in identifying and ordering the rows in the result set. Rownum is a very useful feature in SQL Server, especially when dealing with large datasets, as it allows easy access to specific rows and helps in optimizing database queries.

The Rownum column is not stored in the actual database table but is generated by SQL Server dynamically as part of the query result set.

How to use Rownum in SQL Server?

In SQL Server, you can use Rownum in combination with the SELECT statement to assign a unique number to each row in the result set. Here’s an example:

EmployeeID	FirstName	LastName	Salary	Rownum
1	John	Doe	50000	1
2	Jane	Smith	60000	2
3	Bob	Johnson	45000	3
4	Mike	Brown	55000	4

As you can see, the Rownum column assigns a unique number to each row in the result set based on the order in which they are returned by the query. This helps in identifying and accessing specific rows easily.

Advantages of using Rownum in SQL Server

Using Rownum in SQL Server has several advantages, including:

• Easy access to specific rows in large datasets
• Efficient sorting and ordering of data
• Helps in optimizing database queries
• Useful for pagination and displaying data in chunks

FAQs

What is the syntax for using Rownum in SQL Server?

The syntax for using Rownum in SQL Server is as follows:

SELECT ROWNUM, column1, column2, ...FROM table_nameWHERE conditionsORDER BY column1, column2, ...;

Can Rownum be used with GROUP BY and HAVING clauses?

No, Rownum cannot be used with GROUP BY and HAVING clauses as it assigns a unique number to each row in the result set and does not group or aggregate data.

Is Rownum supported in all versions of SQL Server?

No, Rownum is not supported in all versions of SQL Server. It is supported in Oracle, but in SQL Server, you can use the ROW_NUMBER() function instead.

What is the difference between Rownum and ROW_NUMBER() function?

The main difference between Rownum and ROW_NUMBER() function is that Rownum is a pseudo column in SQL Server that assigns a unique number to each row in the result set, while ROW_NUMBER() is a window function that assigns a unique number to each row in a specified partition based on the order defined by the ORDER BY clause. ROW_NUMBER() is supported in all versions of SQL Server, while Rownum is not.

Can Rownum be used with UPDATE and DELETE statements?

No, Rownum cannot be used with UPDATE and DELETE statements as it is a pseudo column and does not correspond to an actual column in the table.

Can Rownum be used in a subquery?

Yes, Rownum can be used in a subquery to retrieve a specific range of rows based on the Rownum values. Here’s an example:

SELECT *FROM (SELECT ROWNUM, column1, column2, ...FROM table_nameWHERE conditionsORDER BY column1, column2, ...) subqueryWHERE Rownum BETWEEN 10 AND 20;

This query will retrieve rows 10 to 20 based on their Rownum values.

Conclusion

In conclusion, Rownum is a very useful feature in SQL Server that assigns a unique number to each row in the result set. It helps in identifying and accessing specific rows easily, efficient sorting and ordering of data, and optimizing database queries. While Rownum is not supported in all versions of SQL Server, you can use the ROW_NUMBER() function instead. We hope this article has helped you understand Rownum in SQL Server better.