- SQL Server Reference Guide
- Introduction
- SQL Server Reference Guide Overview
- Table of Contents
- Microsoft SQL Server Defined
- SQL Server Editions
- SQL Server Access
- Informit Articles and Sample Chapters
- Online Resources
- Microsoft SQL Server Features
- SQL Server Books Online
- Clustering Services
- Data Transformation Services (DTS) Overview
- Replication Services
- Database Mirroring
- Natural Language Processing (NLP)
- Analysis Services
- Microsot SQL Server Reporting Services
- XML Overview
- Notification Services for the DBA
- Full-Text Search
- SQL Server 2005 - Service Broker
- Using SQL Server as a Web Service
- SQL Server Encryption Options Overview
- SQL Server 2008 Overview
- SQL Server 2008 R2 Overview
- SQL Azure
- The Utility Control Point and Data Application Component, Part 1
- The Utility Control Point and Data Application Component, Part 2
- Microsoft SQL Server Administration
- The DBA Survival Guide: The 10 Minute SQL Server Overview
- Preparing (or Tuning) a Windows System for SQL Server, Part 1
- Preparing (or Tuning) a Windows System for SQL Server, Part 2
- Installing SQL Server
- Upgrading SQL Server
- SQL Server 2000 Management Tools
- SQL Server 2005 Management Tools
- SQL Server 2008 Management Tools
- SQL Azure Tools
- Automating Tasks with SQL Server Agent
- Run Operating System Commands in SQL Agent using PowerShell
- Automating Tasks Without SQL Server Agent
- Storage – SQL Server I/O
- Service Packs, Hotfixes and Cumulative Upgrades
- Tracking SQL Server Information with Error and Event Logs
- Change Management
- SQL Server Metadata, Part One
- SQL Server Meta-Data, Part Two
- Monitoring - SQL Server 2005 Dynamic Views and Functions
- Monitoring - Performance Monitor
- Unattended Performance Monitoring for SQL Server
- Monitoring - User-Defined Performance Counters
- Monitoring: SQL Server Activity Monitor
- SQL Server Instances
- DBCC Commands
- SQL Server and Mail
- Database Maintenance Checklist
- The Maintenance Wizard: SQL Server 2000 and Earlier
- The Maintenance Wizard: SQL Server 2005 (SP2) and Later
- The Web Assistant Wizard
- Creating Web Pages from SQL Server
- SQL Server Security
- Securing the SQL Server Platform, Part 1
- Securing the SQL Server Platform, Part 2
- SQL Server Security: Users and other Principals
- SQL Server Security – Roles
- SQL Server Security: Objects (Securables)
- Security: Using the Command Line
- SQL Server Security - Encrypting Connections
- SQL Server Security: Encrypting Data
- SQL Server Security Audit
- High Availability - SQL Server Clustering
- SQL Server Configuration, Part 1
- SQL Server Configuration, Part 2
- Database Configuration Options
- 32- vs 64-bit Computing for SQL Server
- SQL Server and Memory
- Performance Tuning: Introduction to Indexes
- Statistical Indexes
- Backup and Recovery
- Backup and Recovery Examples, Part One
- Backup and Recovery Examples, Part Two: Transferring Databases to Another System (Even Without Backups)
- SQL Profiler - Reverse Engineering An Application
- SQL Trace
- SQL Server Alerts
- Files and Filegroups
- Partitioning
- Full-Text Indexes
- Read-Only Data
- SQL Server Locks
- Monitoring Locking and Deadlocking
- Controlling Locks in SQL Server
- SQL Server Policy-Based Management, Part One
- SQL Server Policy-Based Management, Part Two
- SQL Server Policy-Based Management, Part Three
- Microsoft SQL Server Programming
- An Outline for Development
- Database
- Database Services
- Database Objects: Databases
- Database Objects: Tables
- Database Objects: Table Relationships
- Database Objects: Keys
- Database Objects: Constraints
- Database Objects: Data Types
- Database Objects: Views
- Database Objects: Stored Procedures
- Database Objects: Indexes
- Database Objects: User Defined Functions
- Database Objects: Triggers
- Database Design: Requirements, Entities, and Attributes
- Business Process Model Notation (BPMN) and the Data Professional
- Business Questions for Database Design, Part One
- Business Questions for Database Design, Part Two
- Database Design: Finalizing Requirements and Defining Relationships
- Database Design: Creating an Entity Relationship Diagram
- Database Design: The Logical ERD
- Database Design: Adjusting The Model
- Database Design: Normalizing the Model
- Creating The Physical Model
- Database Design: Changing Attributes to Columns
- Database Design: Creating The Physical Database
- Database Design Example: Curriculum Vitae
- NULLs
- The SQL Server Sample Databases
- The SQL Server Sample Databases: pubs
- The SQL Server Sample Databases: NorthWind
- The SQL Server Sample Databases: AdventureWorks
- The SQL Server Sample Databases: Adventureworks Derivatives
- UniversalDB: The Demo and Testing Database, Part 1
- UniversalDB: The Demo and Testing Database, Part 2
- UniversalDB: The Demo and Testing Database, Part 3
- UniversalDB: The Demo and Testing Database, Part 4
- Getting Started with Transact-SQL
- Transact-SQL: Data Definition Language (DDL) Basics
- Transact-SQL: Limiting Results
- Transact-SQL: More Operators
- Transact-SQL: Ordering and Aggregating Data
- Transact-SQL: Subqueries
- Transact-SQL: Joins
- Transact-SQL: Complex Joins - Building a View with Multiple JOINs
- Transact-SQL: Inserts, Updates, and Deletes
- An Introduction to the CLR in SQL Server 2005
- Design Elements Part 1: Programming Flow Overview, Code Format and Commenting your Code
- Design Elements Part 2: Controlling SQL's Scope
- Design Elements Part 3: Error Handling
- Design Elements Part 4: Variables
- Design Elements Part 5: Where Does The Code Live?
- Design Elements Part 6: Math Operators and Functions
- Design Elements Part 7: Statistical Functions
- Design Elements Part 8: Summarization Statistical Algorithms
- Design Elements Part 9:Representing Data with Statistical Algorithms
- Design Elements Part 10: Interpreting the Data—Regression
- Design Elements Part 11: String Manipulation
- Design Elements Part 12: Loops
- Design Elements Part 13: Recursion
- Design Elements Part 14: Arrays
- Design Elements Part 15: Event-Driven Programming Vs. Scheduled Processes
- Design Elements Part 16: Event-Driven Programming
- Design Elements Part 17: Program Flow
- Forming Queries Part 1: Design
- Forming Queries Part 2: Query Basics
- Forming Queries Part 3: Query Optimization
- Forming Queries Part 4: SET Options
- Forming Queries Part 5: Table Optimization Hints
- Using SQL Server Templates
- Transact-SQL Unit Testing
- Index Tuning Wizard
- Unicode and SQL Server
- SQL Server Development Tools
- The SQL Server Transact-SQL Debugger
- The Transact-SQL Debugger, Part 2
- Basic Troubleshooting for Transact-SQL Code
- An Introduction to Spatial Data in SQL Server 2008
- Performance Tuning
- Performance Tuning SQL Server: Tools and Processes
- Performance Tuning SQL Server: Tools Overview
- Creating a Performance Tuning Audit - Defining Components
- Creating a Performance Tuning Audit - Evaluation Part One
- Creating a Performance Tuning Audit - Evaluation Part Two
- Creating a Performance Tuning Audit - Interpretation
- Creating a Performance Tuning Audit - Developing an Action Plan
- Understanding SQL Server Query Plans
- Performance Tuning: Implementing Indexes
- Performance Monitoring Tools: Windows 2008 (and Higher) Server Utilities, Part 1
- Performance Monitoring Tools: Windows 2008 (and Higher) Server Utilities, Part 2
- Performance Monitoring Tools: Windows System Monitor
- Performance Monitoring Tools: Logging with System Monitor
- Performance Monitoring Tools: User Defined Counters
- General Transact-SQL (T-SQL) Performance Tuning, Part 1
- General Transact-SQL (T-SQL) Performance Tuning, Part 2
- General Transact-SQL (T-SQL) Performance Tuning, Part 3
- Performance Monitoring Tools: An Introduction to SQL Profiler
- Performance Tuning: Introduction to Indexes
- Performance Monitoring Tools: SQL Server 2000 Index Tuning Wizard
- Performance Monitoring Tools: SQL Server 2005 Database Tuning Advisor
- Performance Monitoring Tools: SQL Server Management Studio Reports
- Performance Monitoring Tools: SQL Server 2008 Activity Monitor
- The SQL Server 2008 Management Data Warehouse and Data Collector
- Performance Monitoring Tools: Evaluating Wait States with PowerShell and Excel
- Practical Applications
- Choosing the Back End
- The DBA's Toolbox, Part 1
- The DBA's Toolbox, Part 2
- Scripting Solutions for SQL Server
- Building a SQL Server Lab
- Using Graphics Files with SQL Server
- Enterprise Resource Planning
- Customer Relationship Management (CRM)
- Building a Reporting Data Server
- Building a Database Documenter, Part 1
- Building a Database Documenter, Part 2
- Data Management Objects
- Data Management Objects: The Server Object
- Data Management Objects: Server Object Methods
- Data Management Objects: Collections and the Database Object
- Data Management Objects: Database Information
- Data Management Objects: Database Control
- Data Management Objects: Database Maintenance
- Data Management Objects: Logging the Process
- Data Management Objects: Running SQL Statements
- Data Management Objects: Multiple Row Returns
- Data Management Objects: Other Database Objects
- Data Management Objects: Security
- Data Management Objects: Scripting
- Powershell and SQL Server - Overview
- PowerShell and SQL Server - Objects and Providers
- Powershell and SQL Server - A Script Framework
- Powershell and SQL Server - Logging the Process
- Powershell and SQL Server - Reading a Control File
- Powershell and SQL Server - SQL Server Access
- Powershell and SQL Server - Web Pages from a SQL Query
- Powershell and SQL Server - Scrubbing the Event Logs
- SQL Server 2008 PowerShell Provider
- SQL Server I/O: Importing and Exporting Data
- SQL Server I/O: XML in Database Terms
- SQL Server I/O: Creating XML Output
- SQL Server I/O: Reading XML Documents
- SQL Server I/O: Using XML Control Mechanisms
- SQL Server I/O: Creating Hierarchies
- SQL Server I/O: Using HTTP with SQL Server XML
- SQL Server I/O: Using HTTP with SQL Server XML Templates
- SQL Server I/O: Remote Queries
- SQL Server I/O: Working with Text Files
- Using Microsoft SQL Server on Handheld Devices
- Front-Ends 101: Microsoft Access
- Comparing Two SQL Server Databases
- English Query - Part 1
- English Query - Part 2
- English Query - Part 3
- English Query - Part 4
- English Query - Part 5
- RSS Feeds from SQL Server
- Using SQL Server Agent to Monitor Backups
- Reporting Services - Creating a Maintenance Report
- SQL Server Chargeback Strategies, Part 1
- SQL Server Chargeback Strategies, Part 2
- SQL Server Replication Example
- Creating a Master Agent and Alert Server
- The SQL Server Central Management System: Definition
- The SQL Server Central Management System: Base Tables
- The SQL Server Central Management System: Execution of Server Information (Part 1)
- The SQL Server Central Management System: Execution of Server Information (Part 2)
- The SQL Server Central Management System: Collecting Performance Metrics
- The SQL Server Central Management System: Centralizing Agent Jobs, Events and Scripts
- The SQL Server Central Management System: Reporting the Data and Project Summary
- Time Tracking for SQL Server Operations
- Migrating Departmental Data Stores to SQL Server
- Migrating Departmental Data Stores to SQL Server: Model the System
- Migrating Departmental Data Stores to SQL Server: Model the System, Continued
- Migrating Departmental Data Stores to SQL Server: Decide on the Destination
- Migrating Departmental Data Stores to SQL Server: Design the ETL
- Migrating Departmental Data Stores to SQL Server: Design the ETL, Continued
- Migrating Departmental Data Stores to SQL Server: Attach the Front End, Test, and Monitor
- Tracking SQL Server Timed Events, Part 1
- Tracking SQL Server Timed Events, Part 2
- Patterns and Practices for the Data Professional
- Managing Vendor Databases
- Consolidation Options
- Connecting to a SQL Azure Database from Microsoft Access
- SharePoint 2007 and SQL Server, Part One
- SharePoint 2007 and SQL Server, Part Two
- SharePoint 2007 and SQL Server, Part Three
- Querying Multiple Data Sources from a Single Location (Distributed Queries)
- Importing and Exporting Data for SQL Azure
- Working on Distributed Teams
- Professional Development
- Becoming a DBA
- Certification
- DBA Levels
- Becoming a Data Professional
- SQL Server Professional Development Plan, Part 1
- SQL Server Professional Development Plan, Part 2
- SQL Server Professional Development Plan, Part 3
- Evaluating Technical Options
- System Sizing
- Creating a Disaster Recovery Plan
- Anatomy of a Disaster (Response Plan)
- Database Troubleshooting
- Conducting an Effective Code Review
- Developing an Exit Strategy
- Data Retention Strategy
- Keeping Your DBA/Developer Job in Troubled Times
- The SQL Server Runbook
- Creating and Maintaining a SQL Server Configuration History, Part 1
- Creating and Maintaining a SQL Server Configuration History, Part 2
- Creating an Application Profile, Part 1
- Creating an Application Profile, Part 2
- How to Attend a Technical Conference
- Tips for Maximizing Your IT Budget This Year
- The Importance of Blue-Sky Planning
- Application Architecture Assessments
- Transact-SQL Code Reviews, Part One
- Transact-SQL Code Reviews, Part Two
- Cloud Computing (Distributed Computing) Paradigms
- NoSQL for the SQL Server Professional, Part One
- NoSQL for the SQL Server Professional, Part Two
- Object-Role Modeling (ORM) for the Database Professional
- Business Intelligence
- BI Explained
- Developing a Data Dictionary
- BI Security
- Gathering BI Requirements
- Source System Extracts and Transforms
- ETL Mechanisms
- Business Intelligence Landscapes
- Business Intelligence Layouts and the Build or Buy Decision
- A Single Version of the Truth
- The Operational Data Store (ODS)
- Data Marts – Combining and Transforming Data
- Designing Data Elements
- The Enterprise Data Warehouse — Aggregations and the Star Schema
- On-Line Analytical Processing (OLAP)
- Data Mining
- Key Performance Indicators
- BI Presentation - Client Tools
- BI Presentation - Portals
- Implementing ETL - Introduction to SQL Server 2005 Integration Services
- Building a Business Intelligence Solution, Part 1
- Building a Business Intelligence Solution, Part 2
- Building a Business Intelligence Solution, Part 3
- Tips and Troubleshooting
- SQL Server and Microsoft Excel Integration
- Tips for the SQL Server Tools: SQL Server 2000
- Tips for the SQL Server Tools – SQL Server 2005
- Transaction Log Troubles
- SQL Server Connection Problems
- Orphaned Database Users
- Additional Resources
- Tools and Downloads
- Utilities (Free)
- Tool Review (Free): DBDesignerFork
- Aqua Data Studio
- Microsoft SQL Server Best Practices Analyzer
- Utilities (Cost)
- Quest Software's TOAD for SQL Server
- Quest Software's Spotlight on SQL Server
- SQL Server on Microsoft's Virtual PC
- Red Gate SQL Bundle
- Microsoft's Visio for Database Folks
- Quest Capacity Manager
- SQL Server Help
- Visual Studio Team Edition for Database Professionals
- Microsoft Assessment and Planning Solution Accelerator
- Aggregating Server Data from the MAPS Tool
All major programming languages, including Transact-SQL, have the concepts of code formatting, scope, error handling, variables, math and statistical functions, and loops. Let's add one more fundamental programming concept to your arsenal.
One of the most powerful tools in programming is recursion. Recursion is similar to a loop, with has one major difference. A loop sets up a condition and then executes a block of code until the condition is met. In contrast, recursion calls itself a number of times, using answers that it provides as an input. Let's examine that a bit further.
By now, you know that the loop construct in T-SQL uses the WHERE clause. A simple loop looks like this:
DECLARE @x INT SET @x = 1 WHILE @x < 11 BEGIN SELECT @x SET @x = @x + 1 END PRINT 'All Done'
Once the condition is set, the system "loops" through the code until it is met. There are no outputs required except the final answer.
Recursion is a bit different. A recursive process also loops until a condition is met, but the process returns an answer at each phase of the process, and then calls itself again using that answer as an input.
A useful example when discussing recursion is a mathematical factorial.
A factorial number is the product of a number's products. What that means is that "4 factorial" 4 * 3 * 2 * 1 would look like this:
4 * 3 = 12 12 * 2 = 24
So 4 factorial, which is written as 4!, is 24. See the progression of 3 (4-1) and the 2 (3-1) in there?
NOTE
It's very common to use factorials to illustrate recursion. But don't let that freeze your notions about factorials. Recursion is just one way to solve a factorial. Among the other methods are Moessner Factorial, Naive Product, Recursive Product, Boiten Split, Recursive Split, Hyper Simple, Hyper Double, Swing Simple, Swing Double, Swing Rational, Swing Rational, Prime Factorization and Repeated Squaring, Prime Factorization and Nested Squaring, and Swing Factorization, to name just a few!
The reason factorials lend themselves so well to the discussion of recursion is that the algebraic formula (as you might have guessed from the numbers above) to compute a factorial is:
N! = N ( N 1 )
Whenever we see that famous "N" variable repeating itself through iteration, the algorithm we're looking for is most likely a recursive one. That formula shows us where the 3 and the 2 used in the 4! example came from.
To compute the factorial algorithm using recursion we need something that calls itself N times, decrementing by one each time, and multiplying itself by that number.
To see recursion in action, let's create a User Defined Function (UDF) to create a Factorial algorithm. (To learn more about functions, check out my previous article here at InformIT.) We'll break this function down line by line to show how it works. We'll use line numbers this time to illustrate, but be sure to take them out to run the code!
1. CREATE FUNCTION dbo.Factorial(@x int ) 2. RETURNS INT 3. AS 4. BEGIN 5. DECLARE @i int 6. IF @x <= 1 7. SET @i = 1 8. ELSE 9. SET @i = @x * dbo.Factorial( @x - 1 ) 10. RETURN (@i) 11. END
In the first line, we've prefaced the function as required with the owner name. This function accepts one input, an integer value.
On the second line we see why we've used a User Defined Function. UDFs can return a value to the calling program. In the case of recursion, the calling program is the function itself. We'll use that feature to complete the first multiplication, and then feed the product back into itself.
The fifth line sets up the feedback value for the whole process. It provides the the value that we need for the next pass.
We've handled the 0 problem in the sixth and seventh lines. Curiously enough, the factorial of 0 (or 0!) is 1, so we handle that separately here. This line also serves as the exit condition for the function.
The ninth line is the primary algorithm. Looking closely we can see the n! = n(n-1) there. The n! part is the i we're working with at that moment. The x is multiplied by a number that this very program provides! To see this in action, let's run the function:
SELECT dbo.factorial(4)
Here's what happened, blow by blow:
The function was called and passed the value 4.
The function checked to see if the passed value was 1 or 0. It wasn't.
The variable @i was set to 4 multiplied by the function with an input of 4 (the original @x) minus 1, which is three. i = 4 ( 4-1). That answer was twelve.
This caused the function to be called again, this time with an input of 12. Steps 1 through 3 were processed again, each time decreasing the first input by 1. This means that 12 was fed back into the function, and this time multiplied by 2 (which is 24). When the decrement went to one the check at line two stopped the process, and the number 24 was returned.
While you might not run into factorials very often, they are useful for understanding recursion. The key things to remember about recursion are how it is both like and unlike a loop. It's important to know when to choose each. The rule of thumb is this: to use a product of an algorithm as its own input, pick recursion. To repeat a block of code a certain number of times, use a loop.
Online Resources
One of the neatest algorithms around showing recursion in Java can be found here. A Java applet walks through this same sort of formula. If you have any confusion in reading this article, set the speed to "slow" on that applet and it will help you understand how the algorithm works. This is way cool!
Recursion often leads to a discussion of handling a "tree" hierarchy. While I normally do this in another programming language, you can do it in T-SQL. There's a great article over at the SQL-Team's Web site that shows you how.
InformIT Tutorials and Sample Chapters
Recursion is used everywhere. Here's an example by Sriranga Veeraraghavan on using recursion in UNIX shell scripts.