Overview of ROW_NUMBER Function in SQL

Summary: The ROW_NUMBER() function in SQL assigns a unique number to each row, aiding in tasks like ranking and pagination. It differs from RANK() and DENSE_RANK() by providing unique numbers without gaps.

Introduction

Structured Query Language, or SQL, is vital for maintaining and modifying relational databases. Database administrators, software developers, data analysts, and many other professionals who work with data utilise it as the industry standard language for communicating with databases.

Aspirants need to understand the ROW_NUMBER function in SQL, so the following blog covers an in-depth evaluation of the same. Accordingly, I have provided a clear and concise evaluation of the row number function that will help you excel in this topic effectively. 

See: What are SQL Aggregate Functions? Types and Importance.

SQL Row Number Function

The SQL ROW_NUMBER() function assigns a unique integer value to each row in the result set. This function often ranks the rows or provides a unique identifier within a specific partition of the result set.

You commonly use the ROW_NUMBER() function with the ORDER BY clause to determine the order in which the system assigns numbers to rows.

Here’s the basic syntax of the ROW_NUMBER() function:

• PARTITION BY (optional): This clause divides the result into partitions or groups. The ROW_NUMBER() function will restart numbering for each partition separately. If you omit this clause, the system treats the entire result set as a single partition.
• ORDER BY: This clause specifies the column(s) by which the rows should be ordered. The ROW_NUMBER() function assigns numbers based on this order. You can specify one or more columns and use the ASC (ascending) or DESC (descending) keyword to control the sorting order.

Explore: Optimising Inventory with Data Analytics and SQL Ranking.

Examples of the ROW_NUMBER Function

Suppose you have a table named “Employees” with columns “EmployeeID,” “FirstName,” and “LastName,” and you want to assign a unique number to each employee based on their last names in alphabetical order:

In this ROW_NUMBER function in SQL, with example:

• The ROW_NUMBER() function assigns a unique number to each row.
• The ORDER BY LastName ASC clause specifies that the rows should be ordered by the “LastName” column in ascending order.
• The result set includes columns for “EmployeeID,” “FirstName,” “LastName,” and the newly assigned “RowNumber.”

The result will display the employees’ respective row numbers based on the alphabetical order of their last names.

Remember that the ROW_NUMBER() function is just one of many window functions available in SQL. It is particularly useful for tasks like ranking, pagination, and generating unique identifiers within specific partitions of your data.

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How do you use the ROW_NUMBER Function in SQL? 

Using the ROW_NUMBER() function in SQL involves applying it to a query to assign a unique row number to each row in the result set. Typically, this function is used with the ORDER BY clause to determine the order in which rows are numbered. Here’s a step-by-step guide on how to use ROW_NUMBER() in SQL:

Formulate your SQL query: Start by writing your SQL query that retrieves the data you want to work with. The query may include filtering conditions, joins, and other operations.

Add the ROW_NUMBER() function: To use ROW_NUMBER(), include it in your SELECT statement. Specify how you want to partition and order the rows. The basic syntax is as follows: 

• column1, column2, …: List the columns you want to retrieve from the table.
• PARTITION BY (optional): Include this clause to partition the result set into groups based on specific columns. Rows within each partition will receive unique row numbers. If you want a single row number for the entire result set, omit this clause.
• ORDER BY: Specify the column(s) by which the rows should be ordered. This determines the order in which row numbers are assigned. You can use ASC for ascending order or DESC for descending order.

Execute the SQL query: Run your SQL query as common in your database management system or SQL client.

Review the result set: The set will include the selected columns and the newly assigned row numbers. These row numbers will be unique within the specified partitions (if any) and follow the specified ordering.

Example

Here’s a practical example using a simple “Employees” table:

In this example, the query retrieves employee data from the “Employees” table for the “Sales” department and assigns each employee a unique row number based on the alphabetical order of their last names.

Row numbers are often used for ranking, pagination, or generating unique identifiers within specific data subsets.

Differences with other SQL Functions

The difference between RANK, DENSE_RANK, and ROW_NUMBER in SQL is crucial for precise data analysis. These functions help rank rows, identify duplicates, and ensure accurate data organisation, leading to better query performance and results interpretation in database management.

RANK()

When more than one row has identical values and would receive the same rank, the RANK() function assigns the same rank to all of them and skips the subsequent rank positions.

After a tie, the system increases the rank value by the number of tied rows. For example, if two rows tie for second place, the following row will receive a rank of 4 instead of 3.

Example:

DENSE_RANK

DENSE_RANK() gives each row in a result set a distinct rank. It awards the same rank to numerous rows with the same values, and doing so would result in gaps in the ranking order. A continuous ranking sequence is achieved by not increasing the rank value after a tie by the number of tied rows.

Example:

ROW_NUMBER()

Without taking ties into account, ROW_NUMBER() assigns a distinct row number to each row within a result set. Each row is assigned a unique number. Each row receives a different number; it does not leave gaps or consider duplicate values.

Example:

To sum up:

• RANK() assigns distinct ranks when there are ties but breaks the ranking order.
• When there are ties, DENSE_RANK() assigns distinct ranks without creating gaps in the ranking order.
• Each row receives a distinct number regardless of ties when using the ROW_NUMBER() function to assign unique row numbers to each row.

Depending on your unique needs, you can choose between these functions. Use DENSE_RANK() to handle ties by assigning the same rank to each tied row without creating gaps. Choose RANK() if you prefer unique ranks and don’t mind gaps in the ranking order. Opt for ROW_NUMBER() if you need a distinct row number for each row.

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Frequently Asked Questions

What does the ROW_NUMBER() function do in SQL?

The ROW_NUMBER() function in SQL assigns a unique integer value to each row in the result set. It is commonly used for creating rankings, unique identifiers, or sorting data within partitions. This versatile function aids in organising and managing query results efficiently.

How is ROW_NUMBER() different from RANK() in SQL?

ROW_NUMBER() provides a unique number to every row without considering ties, meaning each row gets a distinct number. In contrast, RANK() assigns the same rank to tied rows and skips subsequent ranks, leading to gaps. This distinction is crucial for accurate data ranking and sorting.

Can ROW_NUMBER() be used for pagination?

Yes, ROW_NUMBER() is highly effective for pagination in SQL. By assigning unique row numbers, you can easily select specific ranges of rows, such as rows 11-20, which is useful for displaying data across multiple pages in applications or reports.

Conclusion 

From the above blog, you have learned about the Row number function in SQL, which will help you clearly understand the SQL function. Effectively, with proper practice and learning material that you can avail from Data Science courses by Pickl.AI, you can excel in SQL efficiently. Additionally, you can prepare for SQL interview questions and answers with us.