How to Run Function in SQL?

This blog will help you grasp the concept of functions in SQL by providing examples. Additionally, we will guide you through the process of running SQL functions using various methods.

Watch this video on SQL Server tutorials for beginners, which will help you to understand the concepts in depth:

Introduction to Function in SQL

In SQL, a function is like a ready-made tool that helps do specific jobs with data. It can be used in an SQL command to perform tasks like math calculations, working with text, or dealing with dates. SQL provides various built-in functions, such as mathematical functions, string functions, and date functions, to make it easier to work with and analyze data in a database. 

Additionally, users can create their custom functions to meet specific requirements. Functions play a crucial role in simplifying and enhancing the functionality of SQL queries and data manipulation tasks.

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How to Run Function in SQL

Running a function in SQL involves including an SQL statement. Here’s a simple guide on how to do it:

• Choose the Function: Decide which function you want to run. It could be a built-in function provided by your database system or a custom function that you or someone else has created.
• Use the Function in a Query: Integrate the function into a SQL query. For example, if you have a function named calculateTotal that adds up values in a column, you can use it as follows:

SELECT calculateTotal(column_name) AS total_value
FROM your_table;

Replace calculateTotal with the actual function name and column_name with the specific column you want to calculate. The result will be displayed as total_value.

• Understand Function Parameters: Be aware of any input parameters the function might need. For instance, some functions may require you to provide specific values or columns as inputs to perform the desired operation.
• Review Documentation: Check the documentation of your specific database system to ensure you’re using the correct syntax and parameters for the function. Different database systems may have slight variations in how functions are used.
• Execute the Query: Run the SQL query containing the function using the appropriate tools or interfaces provided by your database system.

Various Methods to Run Functions in SQL

In this section, we are going to explore the various methods that are used to run the function in SQL:

Method 1: Executing a Scalar Function in SQL with Parameters

This SQL code defines a user-defined function called CalculateBonusWithPercentage and then tests it on an “Employee” table. Here’s an example:

CREATE FUNCTION dbo.CalculateBonusWithPercentage(
    @salary DECIMAL(10, 2),
    @bonusPercentage DECIMAL(5, 2)
)RETURNS DECIMAL(10, 2)
AS
BEGIN
    DECLARE @bonus DECIMAL(10, 2);
    -- Calculate bonus based on salary and percentage
    SET @bonus = @salary * (@bonusPercentage / 100.0);
    RETURN @bonus;
END;
-- Test the scalar function on the inserted records
SELECT
    EmployeeID,
    FirstName,
    LastName,
    Salary,
    dbo.CalculateBonusWithPercentage(Salary, 10) AS Bonus10Percent,
    dbo.CalculateBonusWithPercentage(Salary, 5) AS Bonus5Percent
FROM Employee;

Output:

Explanation

The SQL code introduces the user-defined function CalculateBonusWithPercentage, calculating bonuses based on employee salary and a specified percentage. Parameters include @salary (precision: 10, scale: 2) and @bonusPercentage (precision: 5, scale: 2). The function returns a decimal bonus (precision: 10, scale: 2). 

It multiplies the salary by the percentage (converted to decimal). The subsequent test on a hypothetical “Employee” table retrieves key columns and computes two bonuses using the function: one at 10% (Bonus10Percent) and another at 5% (Bonus5Percent). This demonstrates the function’s practical application in determining bonuses for employees.

Method 2: Performing Table Function in SQL with Parameters

To execute a table-valued function in SQL with parameters, you can follow the below-mentioned code:

CREATE FUNCTION dbo.GetEmployeesAboveSalaryThreshold(@threshold DECIMAL(10, 2))
RETURNS TABLE
AS
RETURN
(
    SELECT
        EmployeeID,
        FirstName,
        LastName,
        Salary
    FROM
        Employee
    WHERE
        Salary > @threshold
); 
-- Test the table-valued function with parameters
SELECT *
FROM dbo.GetEmployeesAboveSalaryThreshold(70000);

 Output:

Explanation:

This SQL code defines a table-valued function named GetEmployeesAboveSalaryThreshold. The function takes a parameter @threshold (decimal with precision 10, scale 2) and returns a table with columns: EmployeeID, FirstName, LastName, and Salary. The function filters employees from the “Employee” table where the salary exceeds the specified threshold.

In the test phase, the function is applied by selecting all columns from the result of GetEmployeesAboveSalaryThreshold with a threshold of 70000. This demonstrates how the function can be used to retrieve employee information meeting certain salary criteria.

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Method 3: Using a Function in SQL with Multiple Parameters 

To run a function in SQL with multiple parameters, you need to follow the below-mentioned code:

CREATE FUNCTION dbo.CalculateTotalBonus(
    @salary DECIMAL(10, 2),
    @fixedBonus DECIMAL(10, 2),
    @variableBonusPercentage DECIMAL(5, 2)
)
RETURNS DECIMAL(10, 2)
AS
BEGIN
    DECLARE @totalBonus DECIMAL(10, 2);
    -- Calculate total bonus based on salary, fixed bonus, and variable bonus percentage
    SET @totalBonus = @fixedBonus + (@salary * @variableBonusPercentage / 100.0);    
    RETURN @totalBonus;
END;
 -- Test the function with multiple parameters
SELECT
    EmployeeID,
    FirstName,
    LastName,
    Salary,
    dbo.CalculateTotalBonus(70000,2000,5.5) AS TotalBonus
FROM Employee

Ouput:

Explanation:

The SQL code defines a function named CalculateTotalBonus that computes a total bonus based on an employee’s salary, a fixed bonus, and a variable bonus percentage. The function takes three parameters and returns the calculated bonus. In the test phase, the function is used in a SELECT statement on the “Employee” table, showing the total bonus for each employee with specific parameter values.

Method 4: Applying a Function in SQL with Date Parameters

Let us understand the code mentioned below to execute a function in SQL with date parameters:

-- Create a scalar function with a date parameter
CREATE FUNCTION dbo.CalculateAge(
    @birthdate DATE
)
RETURNS INT
AS
BEGIN
    DECLARE @age INT;
    -- Calculate age based on the current date
    SET @age = DATEDIFF(YEAR, @birthdate, GETDATE());
     RETURN @age;
END;
--  Test the function with date parameters
SELECT
    PersonID,
    FirstName,
    LastName,
    Birthdate,
    dbo.CalculateAge('1980-05-15') AS Age
FROM Person

Output:

Explanation:

The SQL code creates a scalar function named CalculateAge with a date parameter (@birthdate). The function calculates and returns the age based on the provided birthdate and the current date. In the test phase, the function is applied to the “Person” table using a SELECT statement. 

It displays columns like PersonID, FirstName, LastName, Birthdate, and a new column, Age, which represents the calculated age using the CalculateAge function with a specific birthdate (‘1980-05-15’). This illustrates how the function can be used to determine the ages of individuals in the database.

Method 5: Running a Function in SQL Without Parameters

Running a function in SQL without parameters involves a straightforward process, which is mentioned in the form of code:

CREATE FUNCTION dbo.GetTotalOrders()
RETURNS INT
AS
BEGIN
    DECLARE @totalOrders INT;
    -- Calculate the total number of orders
    SELECT @totalOrders = COUNT(*) FROM Orders;
     RETURN @totalOrders;
END;
--  Execute the function without parameters
SELECT dbo.GetTotalOrders() AS TotalOrders;

Output:

Explanation:

The SQL code defines a function named GetTotalOrders that calculates and returns the total number of orders from the “Orders” table. The function doesn’t require any parameters. In the execution phase, the function is called without parameters using a SELECT statement, resulting in a new column named TotalOrders that displays the calculated total number of orders. This demonstrates how to run a function in SQL without providing any input parameters, showcasing the total number of orders in this specific example.

Method 6: Implementing a function in SQL with a return value

To execute a function in SQL with a return value, we can use the following SQL command:

CREATE FUNCTION dbo.CalculateSquare(@number INT)
RETURNS INT
AS
BEGIN
    DECLARE @square INT;
     -- Calculate the square of the input number
    SET @square = @number * @number
    RETURN @square;
END;
-- Using the function in a SELECT statement
SELECT dbo.CalculateSquare(25) AS SquareResult;

Output:

Explanation:

The SQL code defines a function named CalculateSquare that takes an integer parameter and returns the square of that number. In this case, the function is applied to the number 25 using a SELECT statement, and the result is displayed as SquareResult. This demonstrates how to use the function to calculate the square of a specific number and retrieve the result in an SQL query.

Also, learn from our blog on MySQL Interview Questions and Answers to crack any interview.

Conclusion

Throughout this blog, we have seen how to run functions in SQL with the help of various methods. This operation in SQL plays a crucial role in the domain of databases, as it helps the SQL developer make their tasks easier by increasing the efficiency of the project given by the organization and saving precious time.

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