Feel Tech Evolution: Introduction to Transact SQL User-Defined Functions

Introduction

SQL Server 2000 supports User-Defined Functions (UDFs) - one or more Transact-SQL statements that can be used to encapsulate code for reuse. User-defined functions cannot make a permanent changes to the data or modify database tables. UDF can change only local objects for this UDF, such as local cursors or variables.

There are three types of UDF in SQL Server 2000:

Scalar functions

Inline table-valued functions

Multistatement table-valued functions

Scalar functions return a single data value (not a table) with RETURNS clause. Scalar functions can use all scalar data types, with exception of timestamp and user-defined data types.

Inline table-valued functions return the result set of a single SELECT statement.

Multistatement table-valued functions return a table, that was built with many TRANSACT-SQL statements.
User-defined functions can be invoked from a query like built-in functions such as OBJECT_ID, LEN, DATEDIFF, or can be executed through an EXECUTE statement like stored procedures.

1 . Scalar Functions

Scalar functions return a data type such as int, money, varchar, real, etc. They can be used anywhere a built-in SQL function is allowed. The syntax for a scalar function is the following:




CREATE FUNCTION [owner_name.] function_name
 ( [{ @parameter_name  scalar_parameter_type [ = default]} [,..n]])
RETURNS scalar_return_type
[WITH <function_option> >::={SCHEMABINDING | ENCRYPTION]
[AS]
BEGIN
 function_body
 RETURN scalar_expression
END


A simple scalar function to cube a number would look like this:


CREATE FUNCTION dbo.Cube( @fNumber float)
 RETURNS float
AS
BEGIN
 RETURN(@fNumber * @fNumber * @fNumber)
END


Surprisingly, user-defined functions (UDFs) support recursion.  Here is an
SQL Server 2000 UDF using the standard factorial example:


CREATE FUNCTION dbo.Factorial ( @iNumber int )
RETURNS INT
AS
BEGIN
DECLARE @i int


 IF @iNumber <= 1
  SET @i = 1
 ELSE
  SET @i = @iNumber * dbo.Factorial( @iNumber - 1 )
RETURN (@i)
END

On Other Example

The following scalar function returns a maximum amount of books sold for a specified title. This function should be executed in pubs database. If the title has no sales, the UDF will return zero.
/* scalar function to return max amount of books sold ** for the specified title_id */ CREATE FUNCTION dbo.udf_max_copies_sold_for_title (@title_id CHAR(6)) RETURNS INT AS BEGIN

DECLARE @qty INT
-- initialize the variable at 0:
SELECT @qty = 0

SELECT 
    @qty = MAX(qty) 
FROM sales 
WHERE
title_id = @title_id

/* If there are no books sold for title_id specified 
** then return 0:
*/
RETURN ISNULL(@qty, 0)

END

Now we can execute this function as follows:

SELECT dbo.udf_max_copies_sold_for_title ('bu2075')

Results:

----------- 
55

2. In-Line Table Functions

In-line table functions are functions that return the output of a single SELECT statement as a table data type. Since this type of function returns a table, the output can be used in joins of queries as if it was a standard table. The syntax for an in-line table function is as follows:






CREATE FUNCTION [owner_name.] function_name
 ( [{ @parameter_name  scalar_parameter_type [ = default]} [,..n]])
RETURNS TABLE
[WITH <function_option>::={SCHEMABINDING | ENCRYPTION}]
RETURN [(] select_statement [)]


An in-line function to return the authors from a particular state would
look like this:


CREATE FUNCTION dbo.AuthorsForState(@cState char(2) )
RETURNS TABLE
AS
RETURN (SELECT * FROM Authors WHERE state = @cState)

Other Example

The following in-line function returns the product name, quantity ordered, and supplier for the top five best sellers in a particular year in the Northwind database:

/* in-line function to return quantity, product name and supplier
** for the top 5 best-selling products within the specified year
*/

CREATE FUNCTION dbo.udf_top_5_best_sellers (@year INT)
RETURNS TABLE
AS
RETURN

SELECT TOP 5 
     SUM(quantity) AS quantity_ordered, 
     a.ProductID, 
     ProductName, 
     CompanyName AS Supplier
FROM [order details] a INNER JOIN products b
   ON a.productid = b.productid
   INNER JOIN suppliers c ON c.supplierid = b.supplierid
   INNER JOIN orders d ON d.orderid = a.orderid
      AND DATEPART(YEAR, OrderDate) = @year
GROUP BY a.productid, productname, CompanyName
ORDER BY 1 DESC

We can execute this function as follows:

SELECT * FROM dbo.udf_top_5_best_sellers (1998)

Results:

quantity_ordered	ProductID	ProductName	Supplier
659	13	Konbu	Mayumi's
546	24	Guaraná Fantástica	Refrescos Americanas LTDA
542	60	Camembert Pierrot	Gai pturage
513	59	Raclette Courdavault	Gai pturage
414	7	Uncle Bob's Organic Dried Pears	Grandma Kelly's Homestead

Alternatively, we can SELECT only the desired columns from this function:

SELECT ProductID, 
        ProductName 
FROM dbo.udf_top_5_best_sellers (1998)

Results:

ProductID	ProductName
13	Konbu
24	Guaraná Fantástica
60	Camembert Pierrot
59	Raclette Courdavault
7	Uncle Bob's Organic Dried Pears

3. Multistatement Table Functions
Multistatement table functions are similar to stored procedures except that they return a table. This type of function is suited to address situations where more logic is required than can be expressed in a single query. The following is the syntax for a multistatement table function:




CREATE FUNCTION [owner_name.] function_name
 ( [{ @parameter_name  scalar_parameter_type [ = default]} [,..n]])
RETURNS TABLE
[WITH <function_option> >::={SCHEMABINDING | ENCRYPTION]
[AS]
BEGIN
 function_body
 RETURN
END

Hierarchical data, such as an organizational structure, is an example of data that cannot be gathered in a single query. The Northwind Company database's Employees table contains a field called ReportsTo that contains the EmployeeID of the employee's manager. GetManagerReports is a multistatement table function that returns a list of the employees who report to a specific employee, either directly or indirectly.




CREATE FUNCTION dbo.GetManagerReports ( @iEmployeeID int )
RETURNS @ManagerReports TABLE
   (
    EmployeeID   int,
    EmployeeFirstName       nvarchar(10),
    EmployeeLastName   nvarchar(20),
 Title    nvarchar(30),
 TitleOfCourtesy   nvarchar(25),
 Extension   nvarchar(4),
    ManagerID   int
   )
AS
BEGIN


 DECLARE


@iRowsAdded int,   -- Counts rows added to
-- table with each iteration
 @PREPROCESSED   tinyint,  -- Constant
for record prior
-- to processing
 @PROCESSING   tinyint,  -- Constant
for record
-- being processed
 @POSTPROCESSED   tinyint  -- Constant for
records that
-- have been processed


 SET @PREPROCESSED   = 0
 SET @PROCESSING   = 1
 SET @POSTPROCESSED   = 2


 DECLARE @tblReports TABLE (
-- Holds employees added with each pass thru source employees table
  EmployeeID    int,
     EmployeeFirstName        nvarchar(10),
     EmployeeLastName    nvarchar(20),
  Title     nvarchar(30),
  TitleOfCourtesy    nvarchar(25),
  Extension    nvarchar(4),
     ManagerID    int,
  ProcessedState    tinyint
 DEFAULT 0
  )




 --Begin by adding employees who report to the Manager directly.
 INSERT INTO @tblReports
 SELECT EmployeeID, FirstName, LastName, Title, TitleOfCourtesy,
Extension, ReportsTo, @PREPROCESSED
  FROM Employees
 WHERE ReportsTo = @iEmployeeID


 --Save number of direct reports
 SET @iRowsAdded = @@ROWCOUNT


 -- Loop through Employees table until no more iterations are necessary
 -- (e.g., no more rows added) to add all indirect reports.
 WHILE @iRowsAdded > 0
 BEGIN
  --Set just added employees ProcessedState to PROCESSING
-- (for first pass)
  UPDATE @tblReports
   SET ProcessedState = @PROCESSING
  WHERE ProcessedState = @PREPROCESSED


  --Add employees who report to Managers in
-- ProcessedState = PROCESSING
  INSERT INTO @tblReports
SELECT e.EmployeeID, e.FirstName, e.LastName, e.Title,
e.TitleOfCourtesy, e.Extension, e.ReportsTo, @PREPROCESSED
   FROM Employees e
INNER JOIN @tblReports r ON e.ReportsTo = r.EmployeeID
  WHERE r.ProcessedState = @PROCESSING
   AND e.ReportsTo <> @iEmployeeID




  --Save number of rows added for this iteration
  SET @iRowsAdded = @@ROWCOUNT


--Set ProcessedState to POSTPROCESSED for Managers whose
--reports were added in this iteration
  UPDATE @tblReports
   SET ProcessedState = @POSTPROCESSED
  WHERE ProcessedState = @PROCESSING
 END


 --Save all data to output table
 INSERT INTO @ManagerReports
SELECT EmployeeID, EmployeeFirstName, EmployeeLastName, Title,
TitleOfCourtesy, Extension, ManagerID
  FROM @tblReports
    RETURN
END

The output of this function would be used in the same manner as a standard table. Figure 1 demonstrates JOINING the output of GetManagerReports with the Employees table to produce a listing of the organizational structure of the Northwind Company:
User function used in JOIN query

Figure 1: User function used in JOIN query.

Other Example

The following multi-statement function accepts a delimited list as a parameter parses the string and returns the table containing each of the values in the parameter.

/* multi-statement function to parse
** a delimited list and turn it into a rowset
** DEFAULT delimiter is comma
*/

CREATE FUNCTION dbo.parse_comma_delimited_integer(
    @list    VARCHAR(8000), 
    @delimiter VARCHAR(10) = ',')

-- table variable that will contain values
RETURNS @tablevalues TABLE (
    item INT)
AS
BEGIN 
  DECLARE @item VARCHAR(255)
 
  /* Loop over the commadelimited list */
  WHILE (DATALENGTH(@list) > 0)
    BEGIN 
      IF CHARINDEX(@delimiter,@list) > 0
        BEGIN
          SELECT @item =
             SUBSTRING(@list,1,(CHARINDEX(@delimiter, @list)-1))
          SELECT @list =
                SUBSTRING(@list,(CHARINDEX(@delimiter, @list) +
                DATALENGTH(@delimiter)),DATALENGTH(@list))
        END

     ELSE
        BEGIN
          SELECT @item = @list
          SELECT @list = NULL
        END
 
   -- Insert each item into temp table
    INSERT @tablevalues (
        item)
    SELECT item = CONVERT(INT, @item) 
   END

 RETURN
END

Now we can execute this function as follows:

SELECT * FROM dbo.parse_comma_delimited_integer 
('39, 549, 324, 3556, 24, 2132, 345', ',')

Results:

item
39
549
324
3556
24
2132
345

The following multi-statement UDF written for the Northwind database finds customers who have bought products in large quantities during a given year. The UDF accepts the year and amount of total sales and returns the customer name, the product that they have bought in large quantities, and all sales representatives who interfaced with these customers within the given year:

CREATE FUNCTION dbo.udf_top_customers_and_reps (
  @year INT, 
  @amount INT)

RETURNS 
  @temp TABLE(
    ProductName VARCHAR(200), 
    CategoryName VARCHAR(200),
    CustomerID CHAR(5),
    CompanyName VARCHAR(200),
    TotalSales INT, 
    EmployeeNames VARCHAR(2000))

AS 
BEGIN

/* populate the temp table with customers that have purchased any product 
* with total sales greater than the specified amount, within the given year
*/

INSERT @temp (
     ProductName ,
     CategoryName ,
     CompanyName ,
     CustomerID ,
     TotalSales 
)


SELECT 
    ProductName, 
    CategoryName, 
    CompanyName, 
    b.CustomerID, 
    SUM(a.UnitPrice * quantity) AS total_sales 
FROM [order details] a 
INNER JOIN orders b ON a.orderid = b.orderid
INNER JOIN products c ON c.productid = a.productid
INNER JOIN customers d ON d.customerid = b.customerid
INNER JOIN categories e ON e.CategoryID = c.CategoryID
WHERE DATEPART(YEAR, OrderDate) = @year
GROUP BY c.ProductName, e.CategoryName, b.CustomerID, 
d.CompanyName, DATEPART(YEAR, OrderDate) 
HAVING SUM(a.UnitPrice * quantity) > @amount
ORDER BY ProductName

/* now get all the employees that have been involved with the customers
* in the given year and return them in a comma-delimited list
*/


DECLARE @CustomerID CHAR(5), 
    @EmployeeName VARCHAR(200)

DECLARE @Employees TABLE (
 EmployeeName VARCHAR(80))

DECLARE CustomerCursor CURSOR FOR
SELECT CustomerID
FROM @temp a 

OPEN CustomerCursor
FETCH NEXT FROM CustomerCursor INTO @CustomerID

WHILE @@FETCH_STATUS = 0
BEGIN

INSERT @employees
SELECT DISTINCT FirstName + ' ' + LastName 
 FROM Employees a INNER JOIN Orders b ON a.EmployeeID = b.EmployeeID
 AND DATEPART(YEAR,OrderDate) = @year
 WHERE b.CustomerID = @CustomerID


/* create a comma-delimited list of employees */

SELECT @EmployeeName = ''
 SELECT @EmployeeName = @EmployeeName + ', ' + EmployeeName
 FROM @Employees 

SELECT @EmployeeName = SUBSTRING(@EmployeeName, 3, LEN(@EmployeeName)-2)



UPDATE @temp
SET EmployeeNames = @EmployeeName
WHERE CustomerID = @CustomerID

DELETE @Employees
FETCH NEXT FROM CustomerCursor INTO @CustomerID
END
CLOSE CustomerCursor
DEALLOCATE CustomerCursor


RETURN
END

The following execution of the function returns customers who have bought any product in amounts of over $10,000 during 1997:

SELECT * FROM dbo.udf_top_customers_and_reps (1997, 10000)

Results:

ProductName	CategoryName	CustomerID	Companyname	TotalSales	EmployeeNames
Côte de Blaye	Beverages	MEREP	Mère Paillarde	10329	Janet Leverling, Laura Callahan, Margaret Peacock, Michael Suyama, Nancy Davolio, Robert King
Côte de Blaye	Beverages	SIMOB	Simons bistro	10540	Andrew Fuller, Margaret Peacock, Robert King

Invoking Functions

There are a few syntax idiosyncrasies to observe when invoking user-defined functions. SQL Server 2000 provides some system-level user-defined functions in the Master database. These system functions are invoked with a slightly different syntax than ones that you would create. System functions that return a table have the following syntax:


 




::function_name ([argument_expr], [,...])


System functions that return a scalar value use this syntax:


function_name ([argument_expr], [,...])


User-created scalar and rowset functions are invoked in exactly the same
manner.  The syntax for invoking a user-created function looks like this:


[database_name] owner_name. function_name ([argument_expr], [,...])

Limitations

User-defined functions do have some restrictions placed upon them. Not every SQL statement or operation is valid within a function. The following lists enumerate the valid and invalid function operations: Valid:

Assignment statements
Control-flow statements
Variable declarations
SELECT statements that modify local variables
Cursor operations that fetch into local variables
INSERT, UPDATE, DELETE statement that act upon local table variables

Invalid:

Built-in, nondeterministic functions such as GetDate()
Statements that update, insert, or delete tables or views
Cursor fetch operations that return data to the client

Performance Implications

Using UDFs will impact the performance of queries. The extent of the performance impact depends upon how and where you use a user-defined function. This is also true of built-in functions. However, UDFs have the potential for more dramatic performance hits than built-in functions. You should exercise caution when implementing functions in your queries and perform benchmarking tests to insure that the benefits of using your functions exceed the performance costs of using them.

Uses for Functions

Check constraints

Scalar user-defined functions can be used as check constraints for columns in table definitions. As long as an argument to the function is a constant or built-in function or an argument is the column being checked, the function may be used to validate the column's value. These UDF check constraints provide the ability to use more complex logic for determining acceptable column values than Boolean expressions or LIKE patterns would allow.
The following function validates that a serial number follows a specific pattern and portions of the serial number match a specific algorithm for a product type.


CREATE FUNCTION dbo.ValidSerialNumber( @nvcSerialNumber nvarchar(50))
RETURNS BIT
AS
BEGIN

DECLARE
@bValid  BIT,
 @iNumber  INT

 --default to invalid serial number
 SET @bValid = 0

 --Home Office Product
 IF @nvcSerialNumber LIKE
'[0-9][A-Z][0-9][A-Z][0-9][0-9][0-9][0-9]'
 BEGIN
  SET @iNumber = CONVERT(int,RIGHT(@nvcSerialNumber,4))
  IF @iNumber % 7 = 2
  BEGIN
   SET @bValid = 1
  END
 END

 -- Video Game
 IF @nvcSerialNumber LIKE '[0-9][0-9][0-9][A-Z][0-9]5[A-Z]'

 BEGIN
  SET @iNumber = CONVERT(int,LEFT(@nvcSerialNumber, 3))
  IF @iNumber % 2 = 0
  BEGIN
   SET @bValid = 1
  END
 END

RETURN ( @bValid)
END

CREATE TABLE dbo.CustomerProduct
(
 CustomerID  int  NOT NULL PRIMARY KEY,
 ProductID  int  NOT NULL,
 SerialNumber  nvarchar(20) NOT NULL
 CHECK(dbo.ValidSerialNumber(SerialNumber) = 1)
)

Computed columns

Scalar functions can be used to compute column values in table definitions. Arguments to computed column functions must be table columns, constants, or built-in functions. This example shows a table that uses a Volume function to compute the volume of a container:



CREATE FUNCTION dbo.Volume (   @dHeight  decimal(5,2),
@dLength  decimal(5,2),
@dWidth decimal(5,2) )
RETURNS decimal (15,4)
AS
BEGIN
 RETURN (@dHeight * @dLength * @dWidth )
END


CREATE TABLE dbo.Container
(
 ContainerID  int  NOT NULL
 PRIMARY KEY,
 MaterialID  int  NOT NULL
REFERENCES Material(MaterialID),
 ManufacturerID  int  NOT NULL
      REFERENCES
Manufacturer(ManufacturerID)
 Height   decimal(5,2) NOT NULL,
 Length   decimal(5,2) NOT NULL,
 Width   decimal(5,2)  NOT NULL,
 Volume AS
  (
   dbo.Volume( Height, Length, Width )
  )
)

You should note that computed columns might be excluded from being indexed if user-defined functions determine their value. An index can be created on the computed column if the user-defined function is deterministic (e.g., always returns the same value given the same input).

Default constraints

Default column values can be set with user-defined functions. UDFs can be very useful when a hard-coded value or built-in function does not suffice. For example, if a doctor's office wished to save a patient's appointment preference, a user-defined function could calculate the default day and time in a function by using the current date/time when the patient's record was created. If the patient's record were created on a Friday at 10:34 AM the AppointmentPref column would default to "Friday at 10:00" using the following function:


CREATE FUNCTION dbo.AppointmentPreference ( @dtDefaultDateTime datetime )
RETURNS nvarchar(50)
AS
BEGIN

DECLARE @nDay   nvarchar(10),
 @nHour  nvarchar(6),
 @nPreference  nvarchar(50),
 @tiHour  tinyint

 --Get date description
 SET @nDay = DATENAME(dw, @dtDefaultDateTime )

 --Find current hour
 SET @tiHour = DATEPART(hh,@dtDefaultDateTime)

 --Use only 12-hour times
 IF @tiHour > 12
 BEGIN
  SET @tiHour = @tiHour - 12
 END

 --Don't allow appointments during lunch
 IF @tiHour = 12
 BEGIN
  SET @tiHour = 1
 END

 -- These are invalid hours
 IF @tiHour IN(5,6,7,8)
 BEGIN
  SET @tiHour = 4
 END

 --Create preference text
 SET @nPreference = RTRIM(@nDay) + '''s at ' +
CONVERT(varchar(2),@tiHour) + ':00'
 RETURN ( @nPreference)
END


CREATE TABLE dbo.Patient
(
 PatientID  int  NOT NULL PRIMARY KEY
      IDENTITY,
 FirstName  nvarchar(20) NOT NULL,
 LastName  nvarchar(20) NOT NULL,
 Addr1   nvarchar(50),
 Addr2   nvarchar(50),
 City   nvarchar(50),
 State   nvarchar(2),
 ZipCode  nvarchar(20),
 HomePhone  nvarchar(20),
 WorkPhone  nvarchar(20),
AppointmentPref nvarchar(50)
DEFAULT (dbo.AppointmentPreference(GETDATE()))

)

Assignments

Scalar user-defined functions can be used to assign values to scalar variables. They may be used in any situation where a scalar built-in function may be used.



DECLARE @fCube  float

SET @fCube = dbo.Cube( 4.5 )

Control flow
Scalar user-defined functions may be used to control program flow when used in Boolean expressions.



IF dbo.ValidSerialNumber('002A15A') = 1
 PRINT 'Yes'

ELSE
 PRINT 'No'

Case expressions
User-defined functions that return a scalar value can be used in any of the cases of CASE expressions. The following example uses the DailySpecial function in a case function to determine what to display for a given day:



CREATE FUNCTION dbo.DailySpecial( @nvcDay nvarchar(10))
RETURNS NVARCHAR(100)
AS
BEGIN

DECLARE @nvcSpecial nvarchar(100)

 SET @nvcDay = UPPER(@nvcDay)

 IF @nvcDay = 'SUNDAY'
  SET @nvcSpecial = 'Roast beef with green beans and
baked potato'

 IF @nvcDay = 'MONDAY'
  SET @nvcSpecial = 'Chopped beef with green bean
casserole'

 IF @nvcDay = 'TUESDAY'
  SET @nvcSpecial = 'Beef stew'

 IF @nvcDay = 'WEDNESDAY'
  SET @nvcSpecial = 'Beef pot pie'

 IF @nvcDay = 'THURSDAY' OR @nvcDay = 'FRIDAY'
  OR @nvcDay = 'SATURDAY'
  SET @nvcSpecial = 'Beef surprise'

RETURN ( @nvcSpecial )
END


--Use output of DailySpecial function
SELECT   Special =
    CASE DateName(dw, getdate())
WHEN 'Sunday' THEN dbo.DailySpecial('Sunday')
         WHEN 'Monday' THEN
dbo.DailySpecial('Monday')
          WHEN 'Tuesday' THEN
dbo.DailySpecial('Tuesday')
 WHEN 'Wednesday' THEN dbo.DailySpecial('Wednesday')
         ELSE 'It's a mystery!'

      END

Alternative to views
Rowset functions, functions that return tables, can be used as alternatives to read-only views. Since views are limited to a single select statement, user-defined functions can provide greater functionality than a view. Powerful logic can be used when determining the records returned, which is not possible within a view. Also, views cannot accept parameters so a separate view must be created if the WHERE clause must change for different search c riteria.
Alternative to temporary tables Rowset functions can be used as alternatives to temporary tables. For example, if you wished to find authors in the Pubs database who sold no books in a particular state, you could create a couple of functions that would generate the desired resultset.
To find the quantity of books sold for a particular author in a given state you could write the following function:



CREATE FUNCTION dbo.AuthorPoularityForState ( @cState Char(2))
RETURNS  TABLE

AS
RETURN (
        SELECT a.au_id, a.au_fname, a.au_lname,
               SUM(s.qty) AS QTY
        FROM Authors a
  INNER JOIN TitleAuthor ta ON a.au_id = ta.au_id
  INNER JOIN Titles t ON t.title_id = ta.title_id
  INNER JOIN Sales s ON s.title_id = t.title_id
  INNER JOIN Stores st ON st.Stor_ID = s.stor_id
 WHERE  st.state = @cState
 GROUP BY a.au_id, a.au_fname, a.au_lname
 ORDER BY QTY DESC, a.au_lname, a.au_fname
   )
END

You could then create another function that would use the output from the first function to find the authors in a particular state that have not had any sales:



CREATE FUNCTION dbo.ReallyBoringAuthorsForState ( @cState Char(2) )
RETURNS TABLE

RETURN(
SELECT a.au_id as AuthorID, a.au_fname AS AuthorFirstName,
 a.au_lname AS AuthorLastName, @cState AS State
 FROM AuthorPopularityForState(@cState ) pa
 RIGHT JOIN authors a ON pa.AuthorID = a.au_id
 WHERE IsNull(pa.UnitsSold, 0) = 0

)

The following SQL statement would list the California authors who had not sold any books:



SELECT AuthorLastName, AuthorFirstName, AuthorID
 FROM ReallyBoringAuthorsForState('CA')
ORDER BY AuthorLastName, AuthorFirstName

List of authors without book sales
Before the release of SQL Server 2000, temporary tables would likely have been used to generate the interim data to be used for the final query output. By using functions instead of temporary tables, potential table name concurrency problems are avoided. Functions also offer greater code reuse than temporary tables.

Friday, 27 April 2012

Introduction to Transact SQL User-Defined Functions

Introduction

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