Functions Fundamentals

Introduction

A function is a section of code that is used to perform an isolated assignment. Once it has performed its assignment, the function can be accessed to present its result(s). That's how functions are using most traditional computer languages. Just as done in those languages, functions in Microsoft SQL Server can be used to perform various types of operations.

In Transact-SQL, a function is considered an object. After creating the function object, it becomes part of a database. You can then execute it when necessary.

1. Start the computer and log in
2. Start Microsoft SQL Server and click Connect
3. In the Object Explorer, expand Databases
4. To create a new database, right-click Databases and click New Database...
5. In the Database Name text box, type IceCreamShop
6. Click OK
7. In the Object Explorer, Right-click Databases and click Refresh
8. Expand the Databases node followed by the IceCreamShop node
9. Under IceCreamShop, right-click Security, position the mouse on New, and click Schema...
10. In the Schema Name, type Payroll
11. Click OK

There are various ways you can start the creation of a function:

• In the Object Explorer, expand the desired database. Expand the Programmatically node. Expand the Functions node. Right-click Scalar-Valued Function and click New Scalar-Valued Function...
  
  
  
  Sample code would be generated for you:
  

  -- ================================================
  -- Template generated from Template Explorer using:
  -- Create Scalar Function (New Menu).SQL
  --
  -- Use the Specify Values for Template Parameters 
  -- command (Ctrl-Shift-M) to fill in the parameter 
  -- values below.
  --
  -- This block of comments will not be included in
  -- the definition of the function.
  -- ================================================
  SET ANSI_NULLS ON
  GO
  SET QUOTED_IDENTIFIER ON
  GO
  -- =============================================
  -- Author:		<Author,,Name>
  -- Create date: <Create Date, ,>
  -- Description:	<Description, ,>
  -- =============================================
  CREATE FUNCTION <Scalar_Function_Name, sysname, FunctionName> 
  (
  	-- Add the parameters for the function here
  	<@Param1, sysname, @p1> <Data_Type_For_Param1, , int>
  )
  RETURNS <Function_Data_Type, ,int>
  AS
  BEGIN
  	-- Declare the return variable here
  	DECLARE <@ResultVar, sysname, @Result> <Function_Data_Type, ,int>
  
  	-- Add the T-SQL statements to compute the return value here
  	SELECT <@ResultVar, sysname, @Result> = <@Param1, sysname, @p1>
  
  	-- Return the result of the function
  	RETURN <@ResultVar, sysname, @Result>
  
  END
  GO

  You can then modify to customize it
• Open an empty Query Editor. Display the Templates Explorer window and expand the Function node. Drag Create Scalar Function (New Menu) and drop it in the Query Editor
  

  -- ================================================
  -- Template generated from Template Explorer using:
  -- Create Scalar Function (New Menu).SQL
  --
  -- Use the Specify Values for Template Parameters 
  -- command (Ctrl-Shift-M) to fill in the parameter 
  -- values below.
  --
  -- This block of comments will not be included in
  -- the definition of the function.
  -- ================================================
  SET ANSI_NULLS ON
  GO
  SET QUOTED_IDENTIFIER ON
  GO
  -- =============================================
  -- Author:		<Author,,Name>
  -- Create date: <Create Date, ,>
  -- Description:	<Description, ,>
  -- =============================================
  CREATE FUNCTION <Scalar_Function_Name, sysname, FunctionName> 
  (
  	-- Add the parameters for the function here
  	<@Param1, sysname, @p1> <Data_Type_For_Param1, , int>
  )
  RETURNS <Function_Data_Type, ,int>
  AS
  BEGIN
  	-- Declare the return variable here
  	DECLARE <@ResultVar, sysname, @Result> <Function_Data_Type, ,int>
  
  	-- Add the T-SQL statements to compute the return value here
  	SELECT <@ResultVar, sysname, @Result> = <@Param1, sysname, @p1>
  
  	-- Return the result of the function
  	RETURN <@ResultVar, sysname, @Result>
  
  END
  GO

• You can open a new empty Query Editor and start typing your code in it

In Transact-SQL, the primary formula of creating a function is:

CREATE FUNCTION SchemaName.FunctionName()

The Name of a Function We already mentioned that, in Transact-SQL, a function is created as an object. As such, it must have a name. In our lessons, here are the rules we will use to name our functions: A name will start with either an underscore or a letter After the first character as an underscore or a letter, the name will have combinations of underscores, letters, and digits A name will not include special characters such as !, @, #, $, %, ^, &, or * We will avoid using spaces in a name  If the name is a combination of words, each word will start in uppercase

For a function to be useful, it must produce a result. This is also said that the function returns a result or a value. When creating a function, you must specify the type of value that the function would return. To provide this information, after the name of the function, type the RETURNS keyword followed by a definition for a data type. Here is a simple example:

CREATE FUNCTION Administration.Addition()
RETURNS Decimal(6,3)

After specifying the type of value that the function would return, you can create a body for the function. The body of a function starts with the BEGIN and ends with the END keywords. Here is an example:

CREATE FUNCTION Administration.Addition()
RETURNS Decimal(6,3)
BEGIN

END

Optionally, you can type the AS keyword before the BEGIN keyword:

CREATE FUNCTION Administration.Addition()
RETURNS Decimal(6,3)
AS
BEGIN

END

Between the BEGIN and END keywords, which is the section that represents the body of the function, you can define the assignment the function must perform. After performing this assignment, just before the END keyword, you must specify the value that the function returns. This is done by typing the RETURN keyword followed by an expression. A sample formula is:

CREATE FUNCTION Administration.Addition()
RETURNS Decimal(6,3)
AS
BEGIN
    RETURN Expression
END

Here is an example

CREATE FUNCTION GetFullName()
RETURNS nvarchar(100)
AS
BEGIN
	RETURN N'Doe, John'
END

1. In the Object Explorer, right-click IceCreamShop and click New Query
2. To create a function, type the following statement:
   

   USE IceCreamShop;
   GO
   
   CREATE FUNCTION Payroll.CalculateWeeklySalary()
   RETURNS Decimal(8, 2)
   AS
   BEGIN
       RETURN 880.44
   END;
   GO

3. To execute the statement, on the SQL Editor toolbar, click the Execute button
4. In the Object Explorer, expand the IceCreamShop node, expand Programmability. Expand Functions. And expand Scalar-Valued Functions. Notice the presence of the CalculateWeeklySalary node

SchemaName.FunctionName()

As an option, you can start with the name of the database in which the function was created. The formula to use is:

DatabaseName.SchemaName.FunctionName()

Because a function returns a value, you can use that value as you see fit. For example, you can use either PRINT or SELECT to display the function's value in the Query Editor. Here is an example that calls the above Addition() function:

PRINT Exercise.dbo.GetFullName();

As an alternative, to call a function, in the Object Explorer, right-click its name, position the mouse on Script Function As, SELECT To, and click New Query Editor Window.

1. Click inside the Query Editor and press Ctrl + A to select everything
2. To execute the function we just created, type the following:

   PRINT IceCreamShop.Payroll.CalculateWeeklySalary();
   GO

3. To execute, press F5

   

4. To specify a column name for the returned value of a function, change the function call as follows:

   SELECT IceCreamShop.Payroll.CalculateWeeklySalary() AS [Weekly Salary];
   GO

5. Press F5 to execute:

   

Because a function in Transact-SQL is treated as an object, it may need maintenance. Some of the actions you would take include renaming, modifying, or deleting a function.

If you create a function and execute it, it is stored in the Scalar-Valued Functions node with the name you gave it. If you want, you can change that name but keep the functionality of the function.

To rename a function, in the Object Explorer, right-click it and click Rename. Type the desired new name and press Enter.

If you create a function and decide that you don't need it any more, you can delete it.

To visually delete a function in the Object Explorer, locate the function in the Functions section, right-click it and click Delete. The Delete Object dialog box would come up. If you still want to delete the function, click OK; otherwise, click Cancel.

To programmatically delete a function: In a Query Editor, type DROP FUNCTION followed by the name of the function and execute the statement In the Object Explorer, right-click the name of the function, position the mouse on Script Function As, DROP To, and click New Query Editor Window Open a new Query Editor associated with the database that contains the function. Display the Templates Explorer and expand the Function node. Drag the Drop Function node and drop it in the empty Query Editor

1. In the Object Explorer, under the Scalar-Valued Functions node, right-click Payroll.CalculateWeeklySalary and click Delete
2. In the Delete Object dialog box, click OK

As mentioned already, in the body of the function, you define what the function is supposed to take care of. As a minimum, a function can return a simple number, typed on the right side of the RETURNS keyword. Here is an example:

CREATE FUNCTION Administration.Addition()
RETURNS int
BEGIN
    RETURN 1
END

You can also declare new variables in the body of the function to help in carrying the assignment. A variable declared in the body of a function is referred to as a local variable. Once such a variable has been declared, it can be used like any other variable. Here is an example:

CREATE FUNCTION Administration.Addition()
RETURNS int
BEGIN
    DECLARE @Number1 int
    SET @Number1 = 588
    RETURN @Number1 + 1450
END

1. Click inside the Query Editor and press Ctrl + A
2. To create a new function, type the following code:
   

   CREATE FUNCTION Payroll.CalculateWeeklySalary()
   RETURNS Decimal(8, 2)
   AS
   BEGIN
   	DECLARE
   		@HourlySalary Decimal(8, 2),
   		@WeeklyHours Real,
   		@FullName varchar(100);
   		SET @HourlySalary = 24.15;
   		SET @WeeklyHours = 42.50;
   	RETURN @HourlySalary * @WeeklyHours
   END;
   GO

3. Press F5 to execute the statement

   

4. Click inside the Query Editor and press Ctrl + A
5. To call the function, type the following code:
   

   SELECT IceCreamShop.Payroll.CalculateWeeklySalary()
   AS [Weekly Salary];
   GO

6. Execute the code by pressing F5

You can involve a function in data entry. As an example, you can call a function that returns a value and assign that value to a column. You can first create your own function and use it, or you can use one of the built-in functions. Normally, the best way is to check the online documentation to find out if the assignment you want to perform is already created. Using a built-in function would spare you the trouble of writing your own function. You can also involve the function in an operation, then use the result as the value to assign to a field. You can also call a function that takes one or more arguments; make sure you respect the rules of passing an argument to a function when calling it.

Functions Parameters

Introduction

In order to carry its assignment, a function can be provided with some values. Put it another way, when you create a function, instead of, or in addition to, local variables, you may want the code that will call the function to provide the values needed to perform the assignment. For example, imagine you want to create a function that would generate employees email addresses when a user has entered a first and last name. At the time you are creating the function, you cannot know or predict the names of employees, including those who have not even been hired yet. In this case, you can write the whole function but provide one or more placeholders for values that would be supplied when the function is called.

An external value that is provided to a function is called a parameter. A function can also take more than one parameter. Therefore, when you create a function, you also decide whether your function would take one or more parameters and what those parameters, if any, would be.   A Parameterized Function We have already seen that a function's name is also followed by parentheses. If the function doesn't use an external value, its parentheses can be left empty. If a function will use an external value, when you create the function, you must specify a name and the type of value of the parameters.

The name of the parameter is preceded by the @ sign, like a variable. Here is an example:

CREATE FUNCTION Administration.Addition(@Number1 Decimal(6,2))

When a function takes a parameter, in the body of the function, you can use the parameter as if you knew its value, as long as you respect the type of that value.

Here is an example:

CREATE FUNCTION Administration.Addition(@Number1 Decimal(6,2))
RETURNS Decimal(6,2)
BEGIN
    RETURN @Number1 + 1450
END

When you call a function that takes one parameter, you must supply a value for that argument. To do this, type the value of the parameter in the parentheses of the function. Here is an example:

Instead of only one parameter, you can also create a function that takes more than one parameter. In this case, separate the parameters in the parentheses of the function with a comma. Here is an example:

CREATE FUNCTION Administration.Addition(@Number1 Decimal(6,2), @Number2 Decimal(6,2))

Once again, in the body of the function, you can use the parameters as if you already knew their value. You can also declare local variables and involve them with parameters as you see fit. Here is an example:

CREATE FUNCTION Administration.Addition(@Number1 Decimal(6,2),
			                @Number2 Decimal(6,2))
RETURNS Decimal(6,2)
BEGIN
    DECLARE @Result Decimal(6,2)
    SET @Result = @Number1 + @Number2
    RETURN @Result
END;
GO

When calling a function that takes more than one parameter, in the parentheses of the function, provide a value for each parameter, in the exact order they appear in the parentheses of the function. Here is an example:

PRINT Exercise.Administration.Addition(1450, 228);

You can also pass the names of already declared and initialized variables. Here is an example that calls the above function:

DECLARE @Nbr1 Decimal(6,2),
        @Nbr2 Decimal(6,2)
SET @Nbr1 = 4268.55
SET @Nbr2 =26.83
SELECT @Nbr1 As First,
       @Nbr2 As Second,
       Exercise.Administration.Addition(@Nbr1, @Nbr2) AS Result

This would produce:

1. Click inside the Query Editor and press Ctrl + A
2. To add arguments, type the following code:
   

   CREATE FUNCTION Payroll.CalculateWeeklySalary(@WeeklyHours Decimal(6,2),
                                         @HourlySalary SmallMoney)
   RETURNS Decimal(8, 2)
   AS  
   BEGIN
       DECLARE @Weekly SmallMoney
       SELECT  @Weekly = @WeeklyHours * @HourlySalary
   
       RETURN @Weekly
   END;
   GO

3. Press F5 to create the function

   

4. Delete the code in the window and replace it with the following:
   

   DECLARE @Hours Decimal(5,2),
           @Hourly SmallMoney
   SELECT  @Hours = 42.50
   SELECT  @Hourly = 18.62
   SELECT  'Hermine Singh' As [Employee Name],
           @Hours As [Weekly Hours],
           @Hourly As [Hourly Salary],
           RealEstate1.Payroll.CalculateWeeklySalary(@Hours, @Hourly)
           	AS [Weekly Salary];
   GO

5. Press F5 to execute the statement
    
   

   

6. Close tMicrosoft SQL Server
7. When asked whether you want to save, click No

When a function with argument is called, a value must be passed for each argument. Here is an example of such a function:

USE Exercise;
GO

CREATE FUNCTION CalculateTaxAmount(@Price money, @Rate decimal(6, 2))
RETURNS decimal(6, 3)
AS
BEGIN
    DECLARE @ResultVar money

    SELECT @ResultVar = @Price * @Rate / 100
    RETURN @ResultVar
END
GO

Here are examples of calling the function:

USE Exercise;
GO
PRINT dbo.CalculateTaxAmount(140.00, 5.75);
PRINT dbo.CalculateTaxAmount(195.95, 5.75);
PRINT dbo.CalculateTaxAmount(250.00, 7.55);
PRINT dbo.CalculateTaxAmount(125.95, 5.75);
GO

This would produce:

8.05
11.27
18.88
7.24

In some cases, if the function is usually called with the same value for an argument, you can specify a default value for that argument. When such a function is called, you can omit the value of the argument.

To specify a default value for an argument, in the parentheses of the function, after the name and data type of the argument, type =, followed by the desired value. Here is an example:

USE Exercise;
GO

CREATE FUNCTION CalculateTaxAmount(@Price money, @Rate decimal(6, 2) = 5.75)
RETURNS decimal(6, 2)
AS
BEGIN
    DECLARE @ResultVar money

    SELECT @ResultVar = @Price * @Rate / 100
    RETURN @ResultVar
END
GO

When calling a function that has a default value for an argument, you don't have to pass a value for that argument, although you can if you want. When calling the function, in the placeholder of the argument, type the DEFAULT keyword. Here are examples of calling the latest version of our function: USE Exercise; GO PRINT dbo.CalculateTaxAmount(140.00, DEFAULT); PRINT dbo.CalculateTaxAmount(195.95, 5.75); PRINT dbo.CalculateTaxAmount(250.00, 7.55); PRINT dbo.CalculateTaxAmount(125.95, default); GO

1. Click inside the Query Editor and press Ctrl + A
2. Type the following:

   USE master;
   GO
   DROP DATABASE IceCreamShop;
   GO
   DROP DATABASE University1;
   GO

3. Press F5 to execute
4. Close Microsoft SQL Server
5. When asked whether you want to save, click No