Www.NovickSoftware.com User-Defined Functions in SQL Server 2005 Andrew Novick 2007.

www.NovickSoftware.com

User-Defined Functionsin SQL Server 2005

Andrew Novick

2007

www.NovickSoftware.com© Copyright 2003-2007 Andrew Novick All rights reserved.

Agenda

What are User-Defined Functions– Three types:

Scalar In-Line Table Valued Multi-statement Table Valued

Why use User-Defined Functions What You Can’t Do With UDFs and Why! Formatting, Naming and Documenting UDFs for Reuse Debugging, Encryption and Schemabinding Performance Implications of UDFs System functions


Transact-SQL User-Defined Functions


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What are User-Defined Functions?

Transact-SQL routines used to encapsulate program logic.


Types of UDFs

T-SQL Scalar UDF T-SQL Inline Table-valued UDF T-SQL Multi-statement Table-valued UDF CLR Scalar CLR Multi-Row CLR Aggregate


T-SQL: Scalar

T-SQL routine with zero or more parameters Returns a single scalar value

CREATE FUNCTION udf_Area ( @Length float , @Width float ) RETURNS floatAS BEGIN

RETURN @Length * @WidthEND


T-SQL: Inline

A View with parameters

CREATE FUNCTION dbo.udf_AuthorsByLetter ( @Letter CHAR(1) ) RETURNS TABLEAS RETURN SELECT * FROM pubs..Authors WHERE LEFT(au_lname, 1) = @Letter


T-SQL: Multistatement

Returns a single defined table

CREATE FUNCTION dbo.udf_FactorialsTAB (@N int ) RETURNS @Factorials TABLE (Number INT, Factorial INT)AS BEGIN DECLARE @I INT, @F INT SELECT @I = 1, @F = 1 WHILE @I < = @N BEGIN SET @F = @I * @F INSERT INTO @Factorials VALUES (@I, @F) SET @I = @I + 1 END -- WHILE RETURNEND


CLR: Scalar

A C# or VB.Net shared function bound to a SQL Function definition


CLR: Multi-Row

A C# or VB.Net Structure or Class that returns a resultset.


CLR: Aggregate

A C# or VB.Net Structure or Class implementing a required set of methods to produce an aggregate result


T-SQL User Defined Functions


Scalar User-Defined Functions (1)

Written in T-SQL like a stored procedure Takes zero or more parameters Return a single value of a scalar data type:

int varchar (30) numeric (18,3)varchar(max) varbinary(max)

Does not return Text, Timestamp, Image


Scalar User-Defined Functions (2)

CREATE FUNCTION udf_Area ( @Length float , @Width float ) RETURNS floatAS BEGIN RETURN @Length * @Width

END


Using Scalar UDFs

SELECT List – SELECT dbo.udf_Area(5.5, 4)

– SELECT … dbo.udf_Area (measured_length * 1000, total_width) FROM…

WHERE CLAUSE JOIN CLAUSE ORDER BY


Ways to Use Scalar User-Defined Functions?

In the SELECT list In the WHERE clause In a CHECK Constraint In the ON clause of a JOIN In an ORDER BY clause


Data Manipulation in T-SQL UDFs

May SELECT from tables and views May not INSERT UPDATE or DELETEExcept to TABLE variables

SELECT dbo.udf_Addr_ZIP5DistanceMI ('02451', '98052')


Profiling UDF Execution

Turn on T-SQL Statement Start/Complete events.

SQL Profiler has a big impact on duration and CPU time.

It’s difficult to use it as a measure of performance for UDFs of T-SQL Statement events are on.


Debugging Scalar UDFsin SQL Server 2000

Query Analyzer Debug Menu is Disabled To Debug create a Stored Procedure

– Call the UDF in the SP– Step into the UDF

Visual Studio .Net Server Explorer allows for direct debugging

Every instance of SQL Server must be run as a domain user, not LocalSystem


Debugging Scalar UDFs in SQL Server 2005

Use Visual Studio 2005 database project


Things You Can’t Do in UDFs

INSERT, UPDATE, DELETE rows– Except to TABLE variables– Not to TEMP tables

Execute Stored Procedures– Extended SPs that don’t return rowsets are OK

DBCC RAISERROR PRINT Use nondeterministic built-in functions! BEGIN CATCH…. END TRY


Deterministic Functions

Deterministic functions return the same result any time they are called with a specific set of input values. Udf_Area (5.5, 4)

Non-deterministic functions don’t.Getdate(), RAND()


Inline Table-Valued UDFs

Return TABLE Are equivalent to a VIEW with parameters. INSERT, UPDATE, DELETE are possible


Multistatement Table-Valued UDFs

Return a table that’s defined in the header Multiple T-SQL statements Can’t change the state of the database My use extended stored procedures that don’t

return rowsets


Encrypting UDFs

Protects the text of the UDF Add the with Encryption keyword

CREATED FUNCTION udf_xxx ()Returns

With Encryption

SQL Server 2000 encryption has been broken! Don’t count on it.


Schemabinding

Create Function () WITH SCHEMABINDING

Prevents the alteration of database objects that are referenced by the UDF

All objects UDFs and Views referenced must also be schemabound.

All Objects referenced must use two part names.


Schemabinding Recommendations

Always bind scalar UDFs when they don’t reference any other object.

Bind UDFs that reference data only when you have a special reason to do so.

Bind inline and multistatement UDFs only to protect your schema from changes.


Error Handling

You will not get the same chance to handle run-time errors that you do in stored procedures or triggers

For scalars, the best solution is usually to return NULL as the result of the function.

BEGIN CATCH…. END TRY not allowed!

Errors can be reported in the SQL Log.


System UDFs (1)

Defined in master Owned by system_function_schema Begin with “fn_” All lower case letters

Referenced with special :: syntax


CLR Functions In SQL Server 2005

Scalar User Defined Functions Multi-Row User Defined Functions User Defined Aggregate


SQLCLR Functions


Types of SQLCLR Code in S2K5

Stored Procedures User Defined Functions User Defined Aggregates User Defined Types Triggers


Assemblies

.Net Code compiled into an IL DLL Assemblies must be added to S2K5 with

CREATE ASSEMBLY

Bits are stored in the database’s sys.assembly_files table

CREATE ASSEMBLY my_assembly_name

FROM ‘\\myserver\directory…path\MyAssembly.dll’


Code Access SecurityPERMISSION_SETs

SAFE EXTERNAL_ACCESS UNSAFE


PERMISSION_SET: Safe

May not access external resources: registry, file system, or network

May not use unmanaged code or PInvoke May access data using the current context but

not via SQLClient or any other data provider No thread processing


PERMISSION_SET: EXTERNAL_ACCESS

May access external resources:registry, file system, network, environment variables

May not use unmanaged code or PInvoke


PERMISSION_SET: UNSAFE

May access external resources May use unsafe code and PInvoke Can use SQLClient and other data providers Can use thread constructs

This is no more unsafe than extended stored procs


SQLCLR User-Defined Functions

Scalar– Return a single value

Multi-Statement UDFs– Returns a single result set

No .Net Inline UDFs


Creating a Scalar UDF

Create the assembly first Then the T-SQL definition:

CREATE FUNCTION udf_myFunction (

@Parm1 int -- First Parameter

, @Parm2 varcharmax – 2nd Parm

) RETURNS BIT

EXTERNAL NAME assemblyname.class.method


Creating Table Valued UDF

Create the assembly Method returns an

IEnumerable CREATE FUNCTION script defines the

schema of the result


Type Considerations

.Net reference types don’t represent NULL System.Data.SQLTypes represent NULL

Use the SQLTypes when possible


Inprocess Data Provider

System.Data.SQLServer Provider Implements the IData* interfaces Parallels the SQLClient Provider Exposes Additional Classes via SQLContext


User Defined Aggregates

Aggregates scalar values into another scalar Uses the SqlUserDefinedAggregate attribute

CREATE AGGREGATE [Product](@Value float) Returns [float] EXTERNAL NAME [SampleAggregate].[SampleAggregate.Product]goGRANT EXEC ON dbo.Product TO PUBLICgo


User Defined Aggregate Class

public class myAggregate

{

public void Accumulate (<input-type> value)

{ }

public <return-type> Terminate()

{ }

public void Init ()

{ }

public void Merge (myAggregate)

{ }

}


Using the User Defined Aggregate

SELECT dbo.product(sample) [Three integers] FROM (SELECT CAST(1.0 as float) as Sample UNION ALL SELECT 3 UNION ALL SELECT 5 ) Numbers

(Result)

Three integers --------------- 15


Performance Experiment

Test on 1,000,000 row table pinned in memory 2 CPU system

Test CPU ElapsedQuery #0 Scan Table 0.8 0.4

Query #1 Udf_txt_CharIndexRev 114.0 172.3

Query #2 Equivalent SQL 2.9 1.5

Query #3 CharIndexRev (.Net) 44.9 52.8


Best Practices

Pick one .Net language Build assemblies with SQL Server in mind Use the most restrictive Permission Set

possible Move as much .Net/CLR code to the middle

tier as possible Test via the SQL Interface


Why Use .Net in S2K5

Replace Extended SP’s with a safer alternative Replace COM automation: sp_OA_* Take advantage of .Net Framework classes Run compute intense algorithms Reuse code Programmer productivity New capabilities not available in T-SQL

– User Defined Types– User Defined Aggregates


Why Use SQLCLR in S2K5

Encapsulation– Functions and Aggregates allow the

encapsulation of business rulesin reusable form.


Why SQLCLR in S2K5

Many tasks that were awkward or difficult to perform in Transact-SQL can be better accomplished by using managed code..."


Why Not use SQLCLR in S2K5

We used to joke that SQL stood for "Scarcely Qualifies as a Language" because it has no I/O and can't format output. Its math library is limited because it isn't a computational language. It doesn't do text searching, list processing, or graphics. The only purposes of SQL are data management and retrieval. Period.

Joe Cleko


Why Not Use SQLCLR in S2K5

$


Why Not Use SQLCLR in S2K5 (2)

Scalability– Application servers MAY scale out easily– Web servers USUALLY scale out easily– Desktops ALMOST ALWAYS scale out– Scaling up SQL Server is expensive


Why Not use .Net in S2K5 (3)

Compare cost per CPU with software licenses:

Compute Location Extra Costs ~$/CPU

Database Server Advanced OS

SQL Enterprise

Management Tools

$20,000

To

$50,000

Web Server Management Tools $4,000

Desktop $1,000


Download Code Samples

Code samples are available with this presentation at:

www.NovickSoftware.com/Presentations.htm


Transact-SQL User-Defined Functions


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Www.NovickSoftware.com User-Defined Functions in SQL Server 2005 Andrew Novick 2007.

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