The User Defined Functions in SQL Server are like functions in any other programming language that accepts the parameters, performing complex calculations, and returning the result value.
Types of Functions in SQL Server
There are two types of functions in SQL Server:
- System Functions: All the built-in functions supported by the SQL are called as System function. We don’t have to bother about the logic inside them because they cannot be modified. For example, Mathematical Functions, Ranking Functions, String Functions, and so on.
- User Defined Functions: SQL Server allows us to create our own functions called as user defined functions. For example, if we want to perform some complex calculations then we can place them in separate function, and store it in the database. Whenever we need the calculation, we can call it. There are two types of SQL user defined functions:
- Scalar Function: It is a function that return single value. Generally, we have to define the function body between BEGIN … END block but for inline scalar function you can omit them. We can use any SQL data type as the return type except text, image, ntext, cursor, and timestamp.
- Table Valued Functions: It is a function that return a table.
- Inline Table valued Functions: This function returns a table data type based on a single SELECT Statement
- Multi Statement Table valued Functions: This function also returns the tabular result set but, unlike the inline table valued function we can use multiple select statements inside the function body.
Advantages of User Defined Functions in SQL Server
- It will prevent us from writing same logic multiple times.
- Within the Database you can create the function once, and call it n number of times.
- SQL user defined functions reduce the compilation time of SQL query by catching the execution plan and reusing them.
- It can help us to separate the complex calculations from the regular SQL query so that, we can understand and debug the query quicker and better.
- It reduce the network traffic because of its cache plan
- Functions can be used in WHERE Clause as well. By this we can limit the number of rows sent to the client.
Syntax of User Defined Functions in SQL Server
The basic syntax behind the SQL Server User defined functions is as shown below:
|
1 2 3 4 5 6 7 8 9 10 |
CREATE FUNCTION Function_Name(@Parameter_Name Data_type, .... @Parameter_Name Data_type ) RETURNS Data_Type AS BEGIN -- Function Body RETURN Data END |
- Return_Type:
- Data Type: Please specify the data type of return value. For example, VARCHAR, INT, FLOAT etc.
- Data: Please specify the return value, and it should match the Data Type. This can be single value or Table
- Function_Name: You can specify any name you wish to give other than the system reserved keywords. Please try to use meaningful names so that you can identify them easily.
- @Parameter_Name: Every function accepts zero or more parameters, it’s completely depends upon the user requirements. While declaring the parameters don’t forget the appropriate data type. For example (@name VARCHAR(50), @number INT)
- Function Body: Any SQL query, or any complex mathematical calculations you want to implement in this particular function.
In this article we will show you, How to write different types of User Defined Functions in SQL Server with example. For this demonstration, We are going to use [MyEmployee table] and [Department] table present in our [SQL Tutorial] Database.
TIP: Please refer Alter User Defined Functions in SQL Server article to understand, How to Rename, Modify, or Delete UDFs.
From the below figure you can observe that, [MyEmployee table] table have fourteen records
And [Department] table have eight records.
Scalar Functions examples
The Scalar User defined functions in SQL Server are very useful when you want to return a single value as the resultant. For example, total sales, or total investments, total loss, or total expenditure etc.
Scalar Function with No parameters
In this simple example we will show you, How to create the Scalar function without any parameters. From the below query you can observe that, we are summing the Yearly Income of the MyEmployee table.
SQL CODE
|
1 2 3 4 5 6 7 8 9 |
-- SQL User Defined Functions - Scalar Functions example USE [SQL Tutorial] GO CREATE FUNCTION NoParameters () RETURNS INT AS BEGIN RETURN (SELECT SUM([YearlyIncome]) FROM [MyEmployees Table]) END |
OUTPUT
Let me show you, How it look in the SQL Management Studio
Let us see the Output
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 |
USE [SQL Tutorial] GO SELECT [EmployeeID] ,[FirstName] ,[LastName] ,[Education] ,[Occupation] ,[YearlyIncome] ,dbo.NoParameters() AS [Average Income] ,[Sales] ,[HireDate] FROM [MyEmployees Table] |
OUTPUT
Scalar Function with parameters
In this example we will show you, How to create the Scalar function with parameters. From the below query you can observe that, we are concating First name and Last Name.
NOTE: We are using SQL SPACE function to provide the space between the First name, and last name.
SQL CODE
|
1 2 3 4 5 6 7 8 9 |
-- SQL User Defined Functions - Scalar Functions example USE [SQL Tutorial] GO CREATE FUNCTION fullName (@firstName VARCHAR(50), @lastName VARCHAR(50)) RETURNS VARCHAR(200) AS BEGIN RETURN (SELECT @firstName + SPACE(2) + @lastName ) END |
Let us see the Output
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 |
USE [SQL Tutorial] GO SELECT [EmployeeID] -- Passing Parameters to fullname Function ,dbo.fullname([FirstName], [lastName]) AS [Name] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Sales] ,[HireDate] FROM [MyEmployees Table] |
OUTPUT
Scalar Function with Where Clause
The following example will accept the var char as the parameter, and finds the sum of the Sales amount, whose Occupation is equal to the parameter that we pass.
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 |
-- SQL User Defined Functions - Scalar Functions example USE [SQL Tutorial] GO CREATE FUNCTION average (@Occupation VARCHAR(50)) RETURNS FLOAT AS BEGIN RETURN (SELECT SUM([Sales]) FROM [MyEmployees Table] WHERE [Occupation] = @Occupation) END |
Let us see the Output
SQL CODE
|
1 2 3 4 5 6 7 8 |
USE [SQL Tutorial] GO SELECT [Occupation] ,SUM([YearlyIncome]) as [Total Income] ,SUM([Sales]) AS [Total Sale] ,dbo.average([Occupation]) AS [Total Sale from Function] FROM [MyEmployees Table] group by [Occupation] |
OUTPUT
Use Scalar Function in Where Clause
In this example we will show you, How to use the Scalar function in the SQL WHERE Clause
SQL CODE
|
1 2 3 4 5 6 7 8 9 |
-- SQL User Defined Functions - Scalar Functions example USE [SQL Tutorial] GO CREATE FUNCTION AverageSale () RETURNS FLOAT AS BEGIN RETURN (SELECT AVG([Sales]) FROM [MyEmployees Table]) END |
Let us see the Output
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 |
USE [SQL Tutorial] GO SELECT [EmployeeID] ,[FirstName] ,[LastName] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Sales] ,[HireDate] FROM [MyEmployees Table] WHERE [Sales] >= dbo.AverageSale() |
OUTPUT
Inline Table valued Functions examples
The Inline function returns a table data type as the retun value based on a single SELECT Statement
Inline Function with No parameters
In this simple example we will show you, How to create an Inline table valued function without any parameters. From the below query you can observe that, we are selecting top 10 records from the MyEmployee table.
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
-- SQL User Defined Functions - Inline Functions example USE [SQL Tutorial] GO CREATE FUNCTION TopTenCustomers () RETURNS TABLE AS RETURN ( SELECT TOP 10 [FirstName] ,[LastName] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Sales] ,[HireDate] FROM [MyEmployees Table] ) |
Let us see the Output
SQL CODE
|
1 2 3 4 |
USE [SQL Tutorial] GO SELECT * FROM [dbo].[TopTenCustomers] () GO |
OUTPUT
Inline Function with Parameters
This example will show you, How to create an Inline table valued function with parameters. From the below query you can observe that, we are selecting the records from the MyEmployee table, Department table using INNER JOIN, whose Occupation is equal to parameter that we pass..
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
-- SQL User Defined Functions - Inline Functions example USE [SQL Tutorial] GO CREATE FUNCTION CustomerbyDepartment (@profession VARCHAR(50)) RETURNS TABLE AS RETURN ( SELECT [FirstName] ,[LastName] ,[Occupation] ,[Education] ,dept.DepartmentName AS Department ,[YearlyIncome] AS Income ,[Sales] FROM [MyEmployees Table] INNER JOIN Department AS dept ON Dept.[id] = [MyEmployees Table].DeptID WHERE [Occupation] = @profession ) |
Let us see the Output
SQL CODE
|
1 2 3 4 5 |
USE [SQL Tutorial] GO SELECT * FROM [dbo].[CustomerbyDepartment] ('Management') GO |
OUTPUT
Multi-select Table valued Functions examples
The Multiple select table valued functions returns the tabular result set but, unlike the inline table valued function we can use multiple select statements inside the function body. In this example we will show you, How to use Multiple statements in one User defined function.
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 |
-- SQL User Defined Functions - Table Valued Functions example USE [SQL Tutorial] GO CREATE FUNCTION CustomerDepartment() RETURNS @customers TABLE ( [EmployeeID] [smallint] NOT NULL, [FirstName] [nvarchar](30) NULL, [LastName] [nvarchar](40) NULL, [Education] [nvarchar](255) NULL, [Occupation] [nvarchar](255) NULL, [YearlyIncome] [float] NULL, [Sales] [float] NULL, [HireDate] [date] NULL, [DepartmentName] [VARCHAR](50) NULL ) AS BEGIN INSERT INTO @customers SELECT [EmployeeID] ,[FirstName] ,[LastName] ,[Education] ,[Occupation] ,[YearlyIncome] ,[Sales] ,[HireDate] ,dept.DepartmentName FROM [MyEmployees Table] INNER JOIN Department AS dept ON Dept.[id] = [MyEmployees Table].DeptID -- Updating the Records UPDATE @customers SET [YearlyIncome] = [YearlyIncome] + 35200 WHERE [Sales] > (SELECT AVG(Sales) FROM [MyEmployees Table]) RETURN END |
ANALYSIS
First, we are creating a table variable called @customers using the following statement
|
1 |
@customers TABLE |
Next, we are inserting the records from [MyEmployee Table], and [Department] table into @customers table variable.
|
1 2 |
INSERT INTO @customers SELECT |
Next, we are updating the Yearly income of all the customers present in the @customers table variable, whose yearly income is greater than the average sales.
|
1 2 |
UPDATE @customers SET [YearlyIncome] = [YearlyIncome] + 35200 WHERE [Sales] > (SELECT AVG(Sales) FROM [MyEmployees Table]) |
Let us see the Output
SQL CODE
|
1 2 3 4 5 |
USE [SQL Tutorial] GO SELECT * FROM [dbo].[CustomerDepartment] () GO |
OUTPUT
Multiple User Defined Function in SQL Server
In this simple example we will show you, How to use multiple User defined functions in single SELECT Statement.
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 |
USE [SQL Tutorial] GO SELECT [EmployeeID] ,dbo.fullName([FirstName], [LastName]) AS Name -- First UDF ,[Education] ,[Occupation] ,[YearlyIncome] ,[Sales] ,[HireDate] FROM [MyEmployees Table] WHERE [Sales] >= dbo.AverageSale() -- Second UDF |
OUTPUT
One UDF inside another UDF in SQL Server
In this simple example we will show you, How to nest or insert one User defined function inside the another User defined function.
SQL CODE
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
USE [SQL Tutorial] GO CREATE FUNCTION CustDepartment (@education VARCHAR(50)) RETURNS TABLE AS RETURN ( SELECT dbo.fullName([FirstName],[LastName]) AS NAME ,[Occupation] ,[Education] ,dept.DepartmentName AS Department ,[YearlyIncome] AS Income ,[Sales] FROM [MyEmployees Table] INNER JOIN Department AS dept ON Dept.[id] = [MyEmployees Table].DeptID WHERE [Education] = @education ) |
Let us see the Output
SQL CODE
|
1 2 3 4 |
USE [SQL Tutorial] GO SELECT * FROM [dbo].[CustDepartment] ('Bachelors') |
OUTPUT
Limitations of User Defined Functions in SQL Server
- We cannot use the User defined functions, shortly called as UDFs to modify the database state.
- UDFs can not return multiple result sets.
- A UDF does not support the error handing such as : TRY..CACHE, RAISEERROR, or @ERROR
- We cannot call a Stored Procedure from UDFs, but we can call an extended Stored Procedure
- A UDF does not support the temporary tables, but it will allows Table variable.
- SET statements are not allowed in UDFs
- The FOR XML Clause is not allowed inside the UDF
Thank you for Visiting Our Blog
Leave a Reply