Scalar Functions in SQL: Simplify, Reuse, and Optimize Your Code

Scalar functions in SQL are user-defined functions that take one or more input parameters and return a single value. Scalar functions are designed to perform operations and return a singular result, such as a number, string, or date. They allow you to encapsulate reusable logic in your queries, making your SQL code more efficient, readable, and maintainable.

In this blog, you’ll explore scalar functions in SQL along with different types, usage, creation, modification, and performance optimization in queries.

Understanding Scalar Functions in SQL

Scalar functions are a powerful feature in SQL that allow you to create reusable logic for common operations, and they can significantly enhance the efficiency of your queries. 

Unlike table-valued functions that return tables, scalar functions return a single value, whether it's a number, string, or date. 

These user-defined functions (UDFs) accept one or more parameters, perform some operation or calculation, and then return a single result.

Understanding concepts like scalar functions and applying the right techniques is essential while managing database queries. Here are the top courses that can help you:

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Scalar functions can simplify your queries, promote code reuse, and improve maintainability. When you find yourself writing the exact calculation or logic in multiple places, scalar functions allow you to encapsulate that logic and call it whenever needed. This means you only write the logic once and use it everywhere.

With a clear understanding of scalar functions, let's examine the different types to see how they can be used in your queries.

Types of Scalar Functions

Scalar functions in SQL come in two primary categories: Built-in Scalar Functions and User-Defined Scalar Functions. Each serves a different purpose and can be used in various scenarios based on your needs.

Let’s break down both types in detail.

1. Built-in Scalar Functions

SQL comes equipped with a rich set of built-in scalar functions. These are ready to use and do not require any creation process. They allow you to perform common operations like string manipulation, mathematical calculations, or date formatting directly within your queries.

Here are a few popular built-in scalar functions you can use:

1. UPPER(): Converts all characters in a string to uppercase.

   SELECT UPPER('hello') -- Result: 'HELLO'

2. LOWER(): Converts all characters in a string to lowercase.

   SELECT LOWER('HELLO') -- Result: 'hello'

3. LEN(): Returns the length of a string (number of characters).

   SELECT LEN('hello') -- Result: 5
   

4. ROUND(): Rounds a number to the specified number of decimal places.

   SELECT ROUND(123.4567, 2) -- Result: 123.46

5. NOW(): Returns the current date and time of the system.

   SELECT NOW() -- Result: 2025-07-09 14:30:00
   

6. FORMAT(): Formats a number, date, or time according to a specified format.

   SELECT FORMAT(12345.678, 'C', 'en-US') -- Result: $12,345.68

These built-in scalar functions are part of the SQL standard and are available in most database management systems (DBMS). They help you handle common operations without the need for custom functions.

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Also Read: Is SQL Hard to Learn? Challenges, Tips, and Career Insights

Now, let’s move on to User-Defined Scalar Functions, where you’ll learn how to create your own custom functions to handle more complex or specific needs.

2. User-Defined Scalar Functions

While built-in scalar functions are great for common tasks, you might need something more tailored to your application’s logic. That’s where user-defined scalar functions come in. These functions give you the ability to define your own logic and encapsulate it in a reusable function.

To create a user-defined scalar function, you use the CREATE FUNCTION statement. This allows you to specify input parameters, write custom logic, and return a single value.

Here’s a basic structure for creating a user-defined scalar function:

CREATE FUNCTION dbo.FunctionName (@Param1 DATATYPE, @Param2 DATATYPE)
RETURNS DATATYPE
AS
BEGIN
    -- Function Logic
    RETURN expression
END

This structure allows you to pass in values (parameters), perform an operation (logic), and return a result.

Example:

Let’s say you want to calculate the total price of a product after applying a discount. Instead of repeating the same logic across queries, you can create a user-defined scalar function to handle this:

CREATE FUNCTION dbo.CalculateTotal(@Price DECIMAL(10,2), @Discount DECIMAL(5,2))
RETURNS DECIMAL(10,2)
AS
BEGIN
    RETURN @Price - (@Price * @Discount / 100)
END

Now, every time you need to calculate the total price after discount, you can simply call this function:

SELECT ProductName, dbo.CalculateTotal(Price, 10) AS DiscountedPrice
FROM Products

Also Read: Top 27 SQL Projects in 2025 With Source Code: For All Levels

Having covered the types of scalar functions, it’s time to understand how they work in SQL queries and how their behavior influences the overall performance.

How Scalar Functions Work?

Scalar functions operate on a single value and return a single result. Unlike other types of functions in SQL, which may return a set of values or tables, scalar functions are designed to process individual data points. They are executed once for each row in a query, which means they can be called within various SQL clauses to perform calculations or transformations on data.

The Execution Process of Scalar Functions

When you use a scalar function in a query, the database engine evaluates the function for every row of data returned by the query. Each row is processed independently.

However, this behavior makes scalar functions powerful, yet sometimes performance-heavy when working with large datasets. Since the function runs for each row, it can slow down queries that return thousands or millions of rows.

Here’s how it works:

• The function is evaluated on a row-by-row basis. The function uses the input values (parameters) from each row, executes its logic, and then returns a result.
• This result can then be used in various places in your query like SELECT, WHERE, HAVING, and ORDER BY.

Let’s look at a simple example of how scalar functions are used to calculate the total price of a product. The function calculates the total by multiplying the price with the quantity.

Example Usage of Scalar Functions

Imagine you are working with a Products table that contains the Price and Quantity columns. You want to calculate the total cost for each product. Instead of manually multiplying the price and quantity in every query, you can create a scalar function to handle the calculation.

Here’s the SQL function that does the job:

CREATE FUNCTION dbo.CalculateTotal(@Price DECIMAL(10,2), @Quantity INT)
RETURNS DECIMAL(10,2)
AS
BEGIN
    RETURN @Price * @Quantity
END

Now, you can use this scalar function in a SELECT query like this:

SELECT ProductName, Quantity, Price, dbo.CalculateTotal(Price, Quantity) AS Total
FROM Products

Optimizing Scalar Functions

If you're working with large datasets, it’s important to use scalar functions carefully. Here are a few strategies to keep in mind:

• Avoid Scalar Functions in WHERE and JOIN: Using scalar functions in WHERE or JOIN conditions can prevent the database engine from optimizing the query, leading to poor performance.
• Consider Inline Expressions: In some cases, replacing scalar functions with inline expressions (like simple arithmetic or built-in functions) can improve performance by eliminating the need for row-by-row execution.
• Use Table-Valued Functions: If you need to return multiple values or rows, consider using a table-valued function (TVF) instead of a scalar function.

Also Read: List of Operators In SQL [With Examples]

After understanding how scalar functions are executed, the next step is learning how to create them.

How to Create a Scalar Function?

Creating scalar functions in SQL is an essential skill for anyone who wants to encapsulate logic and avoid repeating code. These are designed to take inputs, perform calculations or logic, and return a single output value.

Creating a scalar function involves a few essential steps. Here’s how you can go about it:

1. Specify the Function Name: Start by giving your function a meaningful name. This helps you and others understand what the function does. For example, a function that calculates the discount on a price might be called CalculateDiscount.
2. Define the Input Parameters: Next, you need to define the parameters the function will take. Parameters are like placeholders for the values you will pass into the function when you call it.
3. Set the Return Type: Determine the data type of the value your function will return. This can be an INT, DECIMAL, VARCHAR, or any other valid SQL data type.
4. Write the Logic: Inside the BEGIN...END block, write the logic of your scalar function. This could be a mathematical operation, string manipulation, or any other SQL operation.
5. Return the Result: Finally, use the RETURN statement to return the result of the function. This is the value the function will output when called.

Example:

Let’s now create a scalar function that calculates the total price of a product after applying a discount:

CREATE FUNCTION dbo.CalculateDiscount(@Price DECIMAL(10,2), @Discount DECIMAL(5,2))
RETURNS DECIMAL(10,2)
AS
BEGIN
    RETURN @Price - (@Price * @Discount / 100)
END

This function:

• Take two parameters: @Price (the original price) and @Discount (the discount percentage).
• Calculates the discounted price by subtracting the discount amount from the original price.
• Returns the discounted price as a DECIMAL.

Once this scalar function is created, you can use it in your SQL queries like this:

SELECT ProductName, dbo.CalculateDiscount(Price, 10) AS DiscountedPrice
FROM Products

Once you've created a scalar function, you need to know how to call it properly in your SQL queries. 

How to Call a Scalar Function?

Calling a scalar function is straightforward, as it behaves similarly to built-in SQL functions. You pass the required parameters, and it returns the computed result.

To maximize the utility of scalar functions, you’ll often use them in SELECT statements, but they can also be applied in other clauses like WHERE, HAVING, and ORDER BY.

The general format to call a scalar function is as follows.

SELECT dbo.FunctionName(@Param1, @Param2) AS ResultAlias

Example:

If you have a function named MyFunction that adds two integers, you can call it like this:

SELECT dbo.MyFunction(10, 20) AS Result

In this example:

• dbo.MyFunction(10, 20): This calls the function MyFunction with 10 and 20 as input parameters.
• Result: This is the alias given to the result of the function. It can be any name you choose, and it’s the name that will appear in the result set.

Using Scalar Functions in SELECT Statements

The most common place where you’ll use scalar functions is in the SELECT statement. This is where scalar functions truly shine, as they allow you to perform calculations, transformations, or business logic on your data and display the results.

Example:

Let’s say you have a Products table with Price and Quantity columns, and you want to calculate the discounted price for each product using a scalar function. You can call the scalar function directly in the SELECT statement:

SELECT ProductName, dbo.CalculateDiscount(Price, 10) AS DiscountedPrice
FROM Products

In this query:

• dbo.CalculateDiscount(Price, 10): Calls the CalculateDiscount scalar function with Price as the first parameter and 10 (representing a 10% discount) as the second parameter.
• DiscountedPrice: The alias for the result of the scalar function, which will display the discounted price for each product.

After learning how to call a scalar function in your queries, the next step is understanding how to modify these functions when changes in logic or parameters are needed.

Also Read: Free SQL Certification Course Online [2025]

How to Modify a Scalar Function?

To modify an existing scalar function, you use the ALTER FUNCTION statement. This command allows you to update the function’s logic, parameters, or return type without needing to drop and recreate the function. 

Modifying a scalar function is a simple process, but there are key steps to follow to ensure that the function works as expected after the modification.

1. Identify the Function to Modify:

• Make sure you are modifying the correct function. If you have several scalar functions in your database, check their current logic and understand what needs to be updated.

2. Use ALTER FUNCTION:

• To modify an existing function, you must use the ALTER FUNCTION command. Unlike creating a new function, ALTER allows you to keep the function's name and structure intact.

3. Update the Logic:

• Modify the function’s logic inside the BEGIN...END block. Whether it’s changing a formula, adding an extra condition, or including additional parameters, ensure the new logic meets your business rules.

4. Update Parameters (if needed):

• If the function needs new parameters, add them inside the parentheses. However, if you modify the parameters, ensure the signature remains consistent with any calling code or queries. SQL allows you to modify the logic, but parameters should be handled carefully.

5. Test the Function:

• After modifying the function, test it to make sure it returns the expected results. Check the output for various input values to ensure it works as intended.

Example of Change:

Let’s consider that your scalar function CalculateDiscount needs to handle multiple types of discounts. Previously, the function only accepted a discount percentage. Now, you want to modify it to allow both a percentage and a fixed discount amount.

Here’s how you can modify the function:

ALTER FUNCTION dbo.CalculateDiscount(@Price DECIMAL(10,2), @Discount DECIMAL(5,2), @IsPercentage BIT)
RETURNS DECIMAL(10,2)
AS
BEGIN
    IF @IsPercentage = 1
        RETURN @Price - (@Price * @Discount / 100)
    ELSE
        RETURN @Price - @Discount
END

In this updated version:

• A new parameter @IsPercentage is added to decide whether the discount is a percentage or a fixed amount.
• The function now checks the value of @IsPercentage. If it's 1, it calculates the discount as a percentage; otherwise, it treats the discount as a fixed amount.

This update allows more flexibility in how the discount is calculated.

After making adjustments to a scalar function, evaluate whether the modification satisfies your needs or if it’s better to remove the function entirely to streamline your database.

How to Remove a Scalar Function?

To remove a scalar function, you use the DROP FUNCTION statement. This command removes the function from the database entirely, making it no longer available for use in queries. Once a function is dropped, any code or queries that depend on it will throw an error if they try to call the removed function.

Here’s the basic syntax to remove a scalar function:

DROP FUNCTION dbo.FunctionName

Example:

Let’s say a scalar function called dbo.CalculateDiscount was found to have performance issues. It’s been identified that the logic is inefficient and needs to be replaced by a more optimized version. If you want to remove this outdated function, you can execute the DROP FUNCTION command:

DROP FUNCTION dbo.CalculateDiscount

Before you drop a function, it's essential to ensure that the function isn’t being used in active queries or applications.

Considerations Before Removal

Removing a scalar function can have unintended consequences if it’s still being used in other parts of your database or applications. Here's what you need to check before dropping a function:

1. Dependency Check:

• Ensure that no queries, stored procedures, or applications are still relying on the function. Dropping a scalar function that is in use will lead to errors in any SQL queries or processes that reference it.

2. Review Function Usage:

• Before removing the function, you should conduct a review to find all instances where the function is called in your database. This can be done by searching through your SQL code or using database tools to track dependencies.

In SQL Server, you can query system views to check for dependent objects:

 SELECT OBJECT_NAME(object_id) AS FunctionName
FROM sys.sql_expression_dependencies
WHERE referenced_id = OBJECT_ID('dbo.MyFunction')

3. Impact on Business Logic:

• Consider how removing the function might impact your business processes. If the function is used in critical logic, you may need to replace it with a new function or update the logic in the affected queries before removal.

When to Remove a Scalar Function:

• Performance Issues: If a scalar function is causing performance problems, especially with large datasets, it might be time to remove it and replace it with a more efficient solution.
• Redundancy: If you find that the function is no longer needed because the logic is handled elsewhere or through a different approach, it’s best to drop the function.
• Outdated Business Logic: When business rules change, and the function no longer aligns with the new logic, it should be removed to prevent any confusion or incorrect results.

Also Read: Creating MySQL Database Using Different Methods

As you remove scalar functions, understanding their performance implications is crucial, especially since inefficient functions can slow down queries and affect database efficiency.

Performance Considerations

While scalar functions provide powerful ways to encapsulate logic in SQL, their usage can come at a cost. As with any tool, knowing when and how to use scalar functions is vital for maintaining optimal database performance. 

In this section, we'll explore the impact of scalar functions on query performance and discuss best practices to optimize their use.

Impact on Query Performance

One of the primary performance concerns with scalar functions is the row-by-row execution model, also known as RBAR (Row-By-Agonizing-Row). This means that each row in your result set requires the function to execute, which can be very slow when processing large datasets.

Let’s break it down:

1. Row-by-Row Execution (RBAR):

• Scalar functions execute once for each row of data. If you apply a scalar function to a large result set, this leads to performance bottlenecks.
• SQL Server must process each row individually, which prevents it from optimizing the query using parallel execution, thus significantly slowing down query performance.

2. Impact on Parallelism:

• SQL Server optimizes queries by breaking them into smaller tasks that can run concurrently (parallelism). When scalar functions are involved in queries, SQL Server is often unable to parallelize the operation.
• For example, if a scalar function is used in an ORDER BY or WHERE clause, SQL Server may fail to parallelize the query, leading to slower execution times.

Example:

Consider the following query:

SELECT dbo.FormatUsername(DisplayName, Location), Reputation, Id
FROM Users
ORDER BY Reputation DESC

In this query, the scalar function dbo.FormatUsername is applied to each row in the Users table. Since the function needs to process every row individually, SQL Server may not be able to parallelize the query efficiently, leading to longer execution times. This could be especially problematic in databases with millions of rows.

Also Read: Top 10 Real-Time SQL Project Ideas: For Beginners & Advanced

Let’s now look at the best practices to mitigate these performance issues.

Best Practices for Optimization

To ensure your scalar functions do not adversely affect your query performance, it’s important to follow these best practices:

1. Avoid Using Scalar Functions in WHERE, JOIN, or ORDER BY Clauses:

• Scalar functions should not be used in WHERE, JOIN, or ORDER BY clauses as this can prevent SQL Server from using indexes effectively and prevent parallelism.
• For example, using a scalar function in the WHERE clause means SQL must evaluate it for every row before applying any filters, significantly slowing down the query.

2. Consider Inline Expressions Instead of Scalar Functions:

• When possible, replace scalar functions with inline expressions. Inline expressions can be optimized better by SQL Server, and they avoid the row-by-row execution model.

For example, instead of using a function like dbo.CalculateTotal to multiply Price and Quantity, simply perform the multiplication directly in the query:

SELECT ProductName, Price * Quantity AS Total
FROM Products

3. Use Table-Valued Functions (TVFs) for Complex Logic:

• If you need to return multiple values, consider using table-valued functions (TVFs) instead of scalar functions. TVFs allow SQL Server to treat the result set as a table, which can be joined and indexed, resulting in better performance.

4. SQL Server 2019: Scalar UDF Inlining:

• SQL Server 2019 introduced a feature called Scalar UDF Inlining. This feature automatically transforms scalar functions into inline expressions, improving performance by eliminating the need for row-by-row execution.
• To take advantage of this, ensure your database compatibility level is set to 150 or higher. This allows SQL Server to automatically replace scalar functions with more efficient inline code.
• This feature significantly enhances query performance, especially when dealing with large result sets.

You can enable Scalar UDF Inlining by setting the compatibility level:

ALTER DATABASE YourDatabaseName
SET COMPATIBILITY_LEVEL = 150

Example:

If you have a scalar function like dbo.CalculateDiscount, SQL Server 2019 will automatically attempt to inline it into the query, making it much more efficient.

SELECT ProductName, dbo.CalculateDiscount(Price, 10) AS DiscountedPrice
FROM Products

Also Read: 100 MySQL Interview Questions: From Beginner to Advanced

With the performance impact of scalar functions in mind, upGrad’s courses offer the structured learning you need to learn optimization techniques and excel in SQL.

Be Proficient in SQL Scalar Functions with upGrad!

Learning scalar functions in SQL helps you write cleaner and more efficient queries. For optimal performance, avoid using scalar functions in WHERE, JOIN, or ORDER BY clauses. Instead, consider using inline expressions or table-valued functions (TVFs). 

Also, use SQL Server 2019’s Scalar UDF Inlining to convert scalar functions into efficient inline expressions automatically.

If you want to deepen your SQL skills and advance your career, upGrad’s specialized courses are an excellent choice. With expert guidance, structured learning, and real-world applications, you’ll bridge the gap between theory and practice.

Here are some foundational free courses to help you get started.

• Data Structures and Algorithms
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• Advanced SQL: Programming Construct and Stored Functions
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Reference:
https://learn.microsoft.com/en-us/sql/sql-server/what-s-new-in-sql-server-2025