Overview of ROW_NUMBER Function in SQL

Introduction

Structured Query Language, or SQL, is a strong and crucial tool for maintaining and modifying relational databases. Database administrators, software developers, data analysts, and many other professionals that work with data utilize it as the industry standard language for communicating with databases.

Based on the need for aspirants to understand about the ROW_NUMBER function in SQL, the following blog covers in-depth a clear 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. 

SQL Row Number Function:

The SQL ROW_NUMBER() function is a window function used to assign a unique integer value to each row in the result set. This integer value is often used to create a ranking or provide a unique identifier for each row within a specific partition of the result set. 

ROW_NUMBER() is commonly used in conjunction with the ORDER BY clause to determine the order in which rows are assigned numbers.

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

• PARTITION BY (optional): This clause divides the result set into partitions or groups. The ROW_NUMBER() function will restart numbering for each partition separately. If you omit this clause, the entire result set is treated 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 you can use the ASC (ascending) or DESC (descending) keyword to control the sorting order.

Here’re Examples of 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 is used to assign 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 with their respective row numbers based on the alphabetical order of their last names.

Keep in mind 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.

How to use 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 in conjunction 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:

1. 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 as needed.

2. 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): If you want to partition the result set into groups based on specific columns, include this clause. Rows within each partition will receive their own 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.

3. Execute the SQL query: Run your SQL query as you normally would in your database management system or SQL client.

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

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 a unique row number to each employee based on the alphabetical order of their last names.

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

Difference between Rank and Dense_rank and Row_Number in SQL:

1. RANK(): RANK() gives each row in a result set a distinct rank:

When more than one row has identical values and would be given the same rank, RANK() gives them all the same rank and then omits that row from the rest of the ranking list.

After a tie, the rank value will be increased by the quantity of tied rows. For instance, if two rows tie for second place, the following row will be given a rank of 4 rather than 3.

Example:

2. DENSE_RANK():

• Additionally, DENSE_RANK() gives each row in a result set a distinct rank.
• Dense_RANK(), on the other hand, awards the same rank to numerous rows with the same values when 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 quantity of tied rows.

Example:

3. 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 distinct number; it does not leave gaps or take into account duplicate values.

Example:

To sum up:

• When there are ties, RANK() assigns distinct ranks 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() if you need to handle ties by giving each tie the same rank without any gaps. Use RANK() if you want unique ranks and don’t mind gaps in the ranking order. Use ROW_NUMBER() if you only require a distinct row number for each row.

Conclusion 

From the above blog, you have learnt 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 as well with us.