Home > Articles > Data > SQL

SQL Server: Advantages and Drawbacks of User-Defined Functions

  • Print
  • + Share This
Why are UDFs important? What can you do with UDFs that you can't do with stored procedures? Although UDFs are not functionally stronger than stored procedures, they do provide certain advantages. Baya Pavliashvili discusses the advantages and limitations that are associated with UDFs and shows you the coding tasks that qualify as good candidates for UDFs.
Like this article? We recommend

In the previous article in this series, I introduced you to user-defined functions (UDFs), which are excellent tools for certain programming tasks. This article discusses the advantages and limitations that are associated with UDFs, and shows you the coding tasks that qualify as good candidates for UDFs. Hope you find this advice helpful.

Advantages of UDFs

So why are UDFs important? What can you do with UDFs that you cannot with stored procedures? Well, UDFs are not functionally stronger than stored procedures (in fact, UDFs have many limitations, which we will examine shortly). However, UDFs do provide certain advantages, discussed in the following sections.

Execution Within the SELECT Statement

UDFs are executed within an inline query; for instance, you can call a scalar UDF that calculates the number of business days between two dates, as follows:

SELECT dbo.no_of_business_days(date1, date2)

The developer's ability to execute UDF within inline queries makes UDF easier to use than a procedure within other routines. If you had to perform the same calculation in a procedure, you'd have to return the value as an output parameter. Using output parameters isn't necessarily cumbersome, but would involve more coding, as follows:

DECLARE @no_of_business_days INT

EXEC dbo.proc_for_calculating_business_days date1, date2, @no_of_business_days OUTPUT

Execution from Various Parts of SQL Statements

Scalar UDFs can be called from within the WHERE/HAVING clause of queries or even within a SET list of the UPDATE statement. For instance, the following UDF determines the total sales for a given customer within a particular year by using the Northwind database:

CREATE FUNCTION dbo.total_orders (@customerid CHAR(6), @year INT)
RETURNS INT
AS
BEGIN
DECLARE @total INT

SELECT @total = SUM(unitprice * quantity) 
FROM [order details] a INNER JOIN orders b
ON a.orderid = b.orderid
WHERE 
DATEPART(YEAR, orderdate) = @year
AND
customerid = @customerID


RETURN @total
END

This function can be executed within a WHERE clause of the query returning customers who have purchased goods for more than $15,000 in 1996:

SELECT DISTINCT CustomerID 
FROM 
orders a INNER JOIN [order details] b
ON a.orderid = b.orderid
WHERE 
dbo.total_orders(customerID, 1996) > 15000

Results:

CustomerID

ERNSH


UDFs can also be used within a CASE statement; for instance, you can use total_orders UDF to rank customers according to their sales in 1996, as follows:

SELECT CompanyName, 
SalesRank_1996 = CASE
  WHEN dbo.total_orders(customerID, 1996) < 1000 THEN 'poor'
  WHEN dbo.total_orders(customerID, 1996) BETWEEN 1001 AND 5000 THEN 'average'
  WHEN dbo.total_orders(customerID, 1996) BETWEEN 5001 AND 13000 THEN 'good'
  ELSE 'super'
  END
FROM customers

Results (abbreviated list):

CompanyName                                  SalesRank_1996 
----------------------------------------     -------------- 
Alfreds Futterkiste                          super
Ana Trujillo Emparedados y helados           poor
Antonio Moreno Taquería                      poor
Around the Horn                              average
Berglunds snabbköp                           average
Blauer See Delikatessen                      super
Blondesddsl père et fils                     good
Bólido Comidas preparadas                    poor
Bon app'                                     average
Bottom-Dollar Markets                        average

UDF Output Can Be Used as a Rowset

UDFs that return tables can be treated as another rowset. Thus, you can join other tables within your code module to the output of a UDF. For example, if you have a UDF returning two best-selling titles along with their authors, you can easily join it with another table, as follows:

SELECT 
      a.title, 
      a.author_name, 
      b.royalty_amount
FROM dbo.udf_bestselling_titles a INNER JOIN royalty b
ON a.author_id = b.author_id

If you had to use a stored procedure to do the same procedure, you'd have to do the following:

  1. Define a temporary table with the CREATE TABLE statement.

  2. Populate the temporary table with the output of the stored procedure.

  3. Join the temporary table to other tables.

  4. Drop the temporary table at the end of the routine.

Here is the code for a solution that uses a stored procedure instead of a UDF:

CREATE TABLE #temp_table (
    Title_id  INT,
    Title  VARCHAR(200), 
    Author_name VARCHAR(45)
)

INSERT #temp_table (
    title_id, 
    title, 
    author_name )
EXECUTE dbo.usp_bestseller_titles

SELECT 
      a.title, 
      a.author_name, 
      b.royalty_amount
FROM #temp_table a INNER JOIN royalty b
ON a.author_id = b.author_i

UDFs as Parameterized Views

In-line UDFs can be thought of as views that accept parameters. This flavor of UDFs can be used effectively to return different data from the same tables based on the parameter values. For instance, the following UDF will return different categories of titles based on the supplied parameter:

CREATE FUNCTION dbo.udf_category_titles (@category VARCHAR(12))
RETURNS TABLE 
AS
RETURN (
SELECT title, pub_id, price FROM titles 
WHERE 
type = @category)

In-line UDFs can also be used for security—they can return different data based on the user executing the UDF. For instance, the following UDF returns the hire date only if executed by the database owner:

CREATE FUNCTION dbo.udf_get_employee (@p1 INT)
RETURNS TABLE
AS
RETURN
(
SELECT emp_id, fname, lname, 
hire_date = 
CASE WHEN user_name() = 'dbo' THEN CAST(hire_date AS VARCHAR(12)) ELSE 'n/a' END
FROM 
employee 
WHERE job_id = @p1
)

This UDF can be executed as follows:

SELECT * FROM dbo.udf_get_employee(13)

If executed by the database owner, the output is the following:

emp_id          fname                 lname                            hire_date  
---------       --------------------  ------------------------------   ------------ 
PMA42628M       Paolo                 Accorti                          Aug 27 1992 
TPO55093M       Timothy               O'Rourke                         Jun 19 1988 
CGS88322F       Carine                Schmitt                          Jul 7 1992

If executed by any other user, the output will contain "n/a" in the "hire_date" column.

Multi-Statement Functions: Alternatives to Stored Procedures

Multi-statement functions allow you to perform additional logic, such as variable declaration, populating of table variables, and updating values within it, looping through records and more. Multi-statement functions are a great way to rewrite a stored procedure if the following conditions are true:

  • The output of the stored procedure can be used by other routines.

  • Stored procedures don't make any data changes in the permanent tables.

  • The only purpose of the stored procedure is to create a result set that might have to be manipulated prior to returning it to the user.

  • Stored procedures do not perform any tasks prohibited inside the UDFs (see the next section for details).

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020