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Exploring SQL CLR Functions in SQL Server:Question and Answer

Q.1. How to Import SQL CLR Functions?

Ans: SQL CLR functions must return a SqlType. To begin, ensure that your classes that implement SQL CLR functions use a using or Imports statement to import the System.Data.SqlTypes namespace. The C# template for UDFs in SQL Server Database Projects includes the necessary using statement by default; however, you must manually add the statement to the standard Class Library code. After importing the namespace, you can write the functions themselves. You can learn more about SQL CLR functions by enrolling in an online SQL certification course.

Q.2. What is The SqlFunction?

Ans: Functions must be decorated with the SqlFunction attribute in Visual Studio SQL Server Database Projects. This attribute accepts an optional name parameter and works exactly like its SqlProcedure counterpart. Visual Studio SQL Server Database Projects use SqlFunction to deploy SQL CLR functions. The SqlFunction attribute is optional for scalar-valued functions in Class Library projects, so it only emerges in the Class Library sample code for table-valued functions (TVF).

Q.3. Do SqlType Objects (such as SqlString) Require Explicit Instantiation? Explain With The Help of an Example.

Ans: Listing 3-3 shows the sample code for fnHelloWorld from fnTest.cs in the SQLCLRDemo code project, which implements a simple "Hello World" function that returns a SqlString value.

[Sql Function]
public static SqlString fnHelloWorld()
return new SqlString("Hello World");

SqlType objects (such as SqlString) need external instantiation and constructor value passing; you can't just declare and assign values to them. To avoid variable declaration,the code in the following Listing 3-3 illustrates a SqlString object inline inside the return statement.

Q.4. Convert Fahrenheit to Celsius Using SQL CLR Functions.

Ans: A Fahrenheit-to-Celsius conversion function is implemented in Listing 3-4, which contains the code for function fnToCelsius inside fnTest.cs in the SQLCLRDemo sample project.

[Sql Function]
public static SqlDecimal fnToCelsius (Sql Int16 fahrenheit)
return new SqlDecimal((((Int16) fahrenheit) 32) / 1.8);

The function takes a temperature in Fahrenheit as a SqlInt16, transforms it to Celsius, and outputs it as a SqlDecimal. The code casts the input variable from a SqlInt16 to a .NET Int16, then applies a Fahrenheit-to-Celsius conversion formula to the result before passing it to the constructor of a new SqlDecimal object.

Q.5. How To Deploy The SQL CLR Functions?

Ans: Inside the SSDT SQL Server Database Project code version, the SQL CLR functions are automatically deployed. Use the T-SQL CREATE FUNCTION statement in the same way that the CREATE PROCEDURE statement was used in the earlier section, but contain a data type specification for the return value. To deploy the fnHelloWorld function, for example, use the following statement:

The data type nvarchar(4000) corresponds to the SqlString type used in the function's implementation. The WITH EXECUTE AS CALLER clause instructs the SQL CLR function to run as the caller's identity. Learn more about the deployment of SQL CLR functions by enrolling in SQL training courses.

Q.6. How to Test The SQL CLR Functions?

Ans: SQL CLR functions can be tested using SSDT or SSMS. To put the two functions to the test, run the following query. (Alternatively, you can execute the TestScalarFunctions.sql script file inside the SSMS sample project.)

dbo.fnHelloWorld() AS HelloWorld, dbo.fnToCelsius (212) AS CelsiusTemp

Q.7. Can T-SQL Functions Return Sets or Scalar Values?

Ans: T-SQL functions can return both result sets and scalar values. Table-valued functions are functions that return result sets (TVFs). Writing SQL CLR TVFs is possible, but it differs from writing SQL CLR scalar functions or SQL CLR stored procedures. SQL CLR TVFs should return a data type that implements the .NET interface IEnumerable, as well as a "fill row" method for converting an element of that data type to a set of scalar values that creates the corresponding table row.

Q.8. Show an Example of How to Implement Table-Valued Functions(TVF)?

Ans: The code for the functions fnPortfolioTable and FillTickerRow in the SQLCLRDemo sample project's fnTest.cs implements a TVF called fnPortfolioTable.

fnPortfolioTable employs an array rather than its IEnumerable-compatible type. Because arrays in .NET implement IEnumerable, this is perfectly legal. The fnPortfolioTable function takes a semicolon-delimited list of stock ticker symbols. It returns a table with each ticker symbol in an individual row as column TickerSymbol and the ticker's value as column Value. In SQL Server projects, the structure of the returned table is defined in the SqlFunction attribute's TableDefinition parameter, and in Class Library projects, in the CREATE FUNCTION T-SQL command. The assigned values are hard-coded, and no matter how many ticker symbols are passed in, only three rows are returned. Arrays are the name of the game in this case.

The Split method is used first to convert the finite ticker list into an array of single ticker strings. The data is then structured by the TVF so that each element of the return value array (compoundArray) is a two-element array that stores a single ticker symbol and its value. The function code only needs to return a compoundArray. The FillTickerRow function labeled in the SqlFunction attribute's FillRowMethodName parameter then converts the members of each two-element array (passed in as the first parameter) to individual scalars. Because SQL Server requires the FillRowMethodName parameter of the SqlFunction attribute, the fnPortfolioTable function's Class Library version is furnished with that attribute, passing a value for that single parameter. Inside the SQL Server Database Project version, a value for the TableDefinition parameter is also supplied to enable TVF auto-deployment.

Q.9. How to Deploy Table-valued Functions?

Ans: As with the other functions, SSDT deploys a Table-valued function in the SQL Server Database Project sample code. For the Class Library version, use the following T-SQL command (also included in the CreateObjects.sql script file) to deploy the function:

CREATE FUNCTION fnPortfolioTable (@Tickers Packed nvarchar(4000)) RETURNS table (
TickerSymbol nvarchar(5),
Value decimal
AS EXTERNAL NAME SQLCLRDemo.UserDefined Functions.fnPortfolioTable

Q.10. How Can You Give a "Hint" to the Database Table That Your TVF Returns Data in a Specific Order?

Ans: As of SQL Server 2008, you can tell the database table that your TVF returns data in a specific order. This can be used to optimize queries or the creation of indexes based on the same expression. To take advantage of this, first ensure that the logic in your CLR TVF code outputs data in a specific order, and then mention the order in an ORDER clause within the CREATE FUNCTION T-SQL command. Assume that the SQL CLR TVF code ordered its results based on the TickerSymbol column. In that case, you could make the following changes to the T-SQL code that creates the function:

CREATE FUNCTION fnPortfolioTable(@TickersPacked nvarchar (4000)
RETURNS table (

TickerSynbol nvarchar (5),

Value decimal



ORDER (TickerSynbol)

AS EXTERNAL NAME SQLCLRDemo.UserDefinedFunctions.fnPortfolioTable

Although this code does not provide output data in TickerSymbol order, you can still use the preceding T-SQL command to access the TVF's Class Library version. Everything would work properly if you re-run the query in the TestTableValuedFunction.sql script file because the input data is supplied in TickerSymbol order ('IBM;MSFT;ORCL').


SQL CLR functions in SQL Server offer powerful capabilities to extend the functionality of the database using managed code written in .NET languages like C#. By implementing SQL CLR functions, developers can create custom functions that can return scalar values or result sets, providing greater flexibility and efficiency in data processing.In this overview of SQL CLR functions, we explored how to import SQL CLR functions, the importance of the SqlFunction attribute, and the need for explicit instantiation of SqlType objects like SqlString. We also learned how to convert Fahrenheit to Celsius using SQL CLR functions and the process of deploying and testing these functions in SQL Server Database Projects.Additionally, we delved into the implementation of table-valued functions (TVFs) in both SQL Server and Class Library projects. TVFs allow the return of result sets, enhancing the data manipulation capabilities of the database.

Furthermore, we discussed the deployment of TVFs and the possibility of specifying data order for optimization purposes. This hint to the database table can enhance query performance and index creation based on specific expressions.To deepen one's understanding of SQL CLR functions and unlock their full potential, enrolling in SQL server online training courses is highly recommended. These courses provide comprehensive insights into advanced SQL features, including CLR functions, and keep learners updated with the latest developments in the field.Overall, SQL CLR functions provide a bridge between the SQL Server and the .NET framework, enabling developers to leverage the power of managed code within the database engine, leading to enhanced functionality and improved performance for various applications.

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