Understanding the numerous types of variable SQL Server has to offer, and their appropriate usage is one of the cornerstones of developing effective database code. I recently helped a co-worker fix an error message in his code.
-- Error Msg 137, Level 15, State 2, Line 3 Must declare the scalar variable "@l_INT".
The code snippet looked something like this, which led to a discussion about scope of T-SQL variables and an interesting way to fix this problem.
CREATE TABLE #scope_test1 (col1 INT); CREATE TABLE #scope_test2 (col1 INT); GO DECLARE @l_INT INT = 42; INSERT INTO #scope_test1 (col1) SELECT @l_INT; GO INSERT INTO #scope_test2 (col1) SELECT @l_INT; GO
T-SQL language supports local variables (their names begin with a single @). The scope of a variable is the range of Transact-SQL statements that can reference the variable. The scope of a variable lasts from the point it is declared until the end of the batch or stored procedure in which it is declared. A T-SQL batch is a group of statements that SQL Server parses as a single unit. A batch can be delimited by the BEGIN..END statements, or a client tool like SQL Server Management Studio (SSMS) can specify the end of a batch with a GO command (you can set any word to be a batch separator in SSMS, but we will leave that discussion for another time). The names of some Transact-SQL system functions begin with two at signs (@@). They are commonly referred to as Global variables. Global variable names begin with a @@ prefix. You do not need to declare them, since the server constantly maintains them. They are system-defined functions not variables and do not have the same behaviors as variables. All the global variables represent information specific to the server or a current user sessions. Some of the commonly used ones are @@ERROR, @@IDENTITY, @@VERSION. Traditionally, DECLARE command is used to declare a local variable and SET or SELECT used to initialize its value. With SQL Server 2012, both of these tasks can be accomplished in a single statement ;
DECLARE @MyCounter INT = 12 ;
The variables we discussed so far are scalar variables, which can hold a single data value of a specific type. A table variable is a special data type that can be used to store a result set for processing at a later time. table is primarily used for temporary storage of a set of rows returned as the result set of a table-valued function. Functions and variables can be declared to be of type table. table variables can be used in functions, stored procedures, and batches. A DECLARE statement (similar to local scalar variables) is used to DECLARE a table variable. While they behave exactly like local variables, with a well defined scope,they can be thought of as being similar to temporary table, but with several limitations.
The SQLCMD utility lets you enter Transact-SQL statements, system procedures, and script files at the command prompt, in Query Editor in SQLCMD mode, in a Windows script file or in an operating system (Cmd.exe) job step of a SQL Server Agent job. This utility uses ODBC to execute Transact-SQL batches. Scripting variables can be used in SQLCMD scripts. Scripting variables enable one script to be used in multiple scenarios. The setvar command is used to define scripting variables. Variables that are defined by using the setvar command are stored internally. Scripting variables should not be confused with environment variables that are defined at the command prompt by using SET.
The scope of a SQLCMD scripting variable can span several batches, which can be used to implement variables that don’t go out of scope even when a batch ends. The example below is a simplified demo of the same ;
:setvar l_int "42" CREATE TABLE #scope_test1 (col1 INT); CREATE TABLE #scope_test2 (col1 INT); GO INSERT INTO #scope_test1 (col1) SELECT $(l_int); GO INSERT INTO #scope_test2 (col1) SELECT $(l_int); GO -- Results (1 row(s) affected) (1 row(s) affected)
A review of the types of variables the T-SQL language has to offer, has helped refresh my understanding of their appropriate usage.
- Table Variables – http://msdn.microsoft.com/en-us/library/ms175010.aspx
- T-SQL Variables – http://msdn.microsoft.com/en-us/library/ms187953(v=sql.105).aspx
- Global Variables – http://www.codeproject.com/Articles/39131/Global-Variables-in-SQL-Server
- Scripting variables with SQLCMD – http://msdn.microsoft.com/en-us/library/ms188714.aspx
- SQLCMD utility – http://msdn.microsoft.com/en-us/library/ms162773.aspx
BIBrews is a unique opportunity for like-minded technology experts to informally gather for drinks and food and discuss the pressing questions around Business Intelligence and SQL technical trends and experiences. The content is unrehearsed and open. BIBrews has a strict “no sales” and “no recruiting” policy.
The first meeting of STL BIBrews is scheduled for Thursday Dec 13,2012 from 5:30 PM to 8:30 PM (CST) in St.Louis, MO. Please register at EventBrite using this link – http://bibrewsstl.eventbrite.com/ . You can follow Scott Shaw on twitter (@shawsql) and/or @BIBrews for latest updates.
SQL Saturday #154 | St.Louis on Sept 15th 2012, was the first SQL Saturday event in St.Louis, I am happy to say that we started off the SQL Saturday series in St.Louis ( yes, there will be one next year as well !) on a great note. We had over 130 attendees, 11 onsite sponsors and 25 technical sessions spread across 5 classrooms.
Center for Application of Information Technology (CAIT) at WashU, generously offered the venue (6 awesome classrooms plus the common areas and facilities) to host this event. The support of sponsors played a huge role in making this event successful. We got local as well as national sponsors, plus plenty of SWAG sponsors as well. Within a month of opening our call for speakers, we had over 55 sessions submitted for this event. They were a great mix of new and experienced speakers, both local and out of town, on topics ranging across Database Administration, Application Development, Business Intelligence and Professional Development. The real challenge was selecting only 25 sessions and the selection committee put a lot of thought into coming up with the session schedule for the event.
Our team took some time to review the event, which will help us make the next St.Louis SQL Saturday even better event. Feedback from attendees, sponsors, speakers and volunteers was crucial for the team to pin-point areas of improvement.
- The duration of the overall event should be constrained from 9 AM to 4 PM, by either cutting down the session duration from 75 to 60 minutes or possibly having 4 sessions per classroom. We are trying to secure more classrooms at the venue to make this feasible, so that the total number of session offerings during the event remains the same.
- We heard great feeback about the location and quality of the recommended event hotel, and we plan to continue the same for next year
- We will definitely invest in bigger and more number of signs on the sidewalks around the venue, to make it easier for attendees to find their way to the parking area, registration desk and locate the facilities in the venue.
- We are also looking at offering a better packaged box lunch and making some healthy meal options available for next year, not only for lunch, but also for breakfast, snacks and beverages.
- The SPEEDPASS worked out very well and we were able to move attendees efficiently through the registration process. We will probably do an online ONLY version of the event schedule for next year, to mitigate any confusion arising out of last minute schedule changes.
- We plan to leverage Twitter and Linkedin for communicating a majority of updates to event attendees , and use emails ONLY for crucial milestones during the days leading up to the event
Our team is always happy to hear feedback from the attendees and we have plenty of new ideas for the next year’s event. We do have some resource constraints, considering the fact that the event is free to attend, and all of the organizers are volunteers. The event sponsorship, availability of speakers, venue, and costs can change from one year to another and our team will strive to continue providing a valuable learning experience at the event. Organizing a SQL Saturday event, represents team work at its best. On that note, I would like to thank everyone involved; the core team, all the volunteers, PASS & community mentors, sponsors, speakers and friends & family for a successful first SQL Saturday in St. Louis.
SQL Saturday #145 was my first trip to Nashville and I must say I am impressed with the city. The recommended event hotel was located in a very nice part of the town , a short drive from the Randor Lake State park and the weather on Friday evening was just perfect for a walk in the park.
The Event venue, David Lipscomb University, was also a short a drive from the recommended hotel and has a very scenic campus. There were plenty of signs and the location was fairly easy to find. The registration desk was well managed and the breakfast was excellent. I picked up my Speaker shirt and went looking for my friends !
I met with Kathi Kellenberger (b|t), Malathi Mahadevan (b|t), Kevin Kline (b|t) , David Klee (b|t) and Rick Morlean (b|t) on the morning of the event. I was particularly excited about my 11:00 AM session on Parameter Sniffing, as I had recently updated all of my demos to run on SQL Server 2012. My session was very well received and I got a great set of attendees who were very much interested in learning about Parameter sniffing. The session slide deck and demo scripts are available for download on SQL Saturday #145 website.
After my session, I spent a good deal of time talking to attendees, other speakers, organizers and sponsors. The organizers did a great job with putting up a spectacular SQL Saturday and I would like to thank them for the opportunity to speak at this event. This was my last SQL Saturday for the year and i look forward to more SQL Saturdays in 2013 !
I have two speaking engagements coming up this week, that I am really excited about. I have my very first webinar coming up on 10/11/2012. Pragmatic works is giving me an opportunity to present my session on Parameter Sniffing with their Free Training on the T’s webinar series. You can click here to register for this webinar, scheduled at 11.oo AM EST on 10/11. Though I have presented this session at several SQL Saturdays in the past, I am looking forward to my very first experience with delivering this session through a webinar!
My second speaking engagement for this week is at SQL Saturday #154 in Nashville, on 10/13/2012. I will be talking about Parameter Sniffing at 11.00 AM in Room 2. You can click here for the full event schedule, and if you haven’t already signed up for this event, you can register here. I have recently updated my demos for this session to run on SQL Server 2012, so I am really looking forward to presenting them. SQL Saturday #145 not only has an exciting session line up on the event day, but also 4 fantastic pre-cons on Friday 10/12. This will also be my first trip to Nashville, the “Music City” and I plan on visiting the Country Music Hall of Fame!
SQL Saturday #154, the first SQL Saturday in St.Louis is almost here (Sept 15) and I wanted to share some details of this exciting upcoming event.
This event will be held Sep 15th, 2012 at the CAIT Campus of Washington University in St.Louis. The Street address of the venue is – 5 Jackson Avenue, Center for Application of Information technology (CAIT) at Washington University in St.Louis, Clayton, MO 63105. Please follow this link for directions to the venue. The venue is only a short walk from the recommended hotel (Crowne Plaza Clayton). There is free parking for the event attendees in the attached parking Garage (Lot #60) on saturday, you do not need any parking pass or permit. The Garage can be accessed via Lee avenue. From this Garage, take the elevators to Level 1 and follow the signs for SQL Saturday #154 Registration desk. The registration desk will be open for attendees from 7.30 AM and the first 100 attendees to come in with a SPEEDPASS will get a free event t-shirt ! There will be coffee and donuts for breakfast (first come first served!). The first session for the day starts at 8.30 AM.
CAIT has generously offered the use of their facilities to host the event and we would like to remind all of our attendees be respectful of their premises. We do want to make sure they will continue supporting us next year. We have 200 registered attendees (unfortunately, there are still 60+ on the waitlist!), 25 awesome sessions , and 16 sponsors (11 onsite) ! This is going to be a big event in a tight space and it would help for all the attendees to familiarize themselves with the classroom locations in the building.
We will be bringing in lunch boxes from Amighetti’s , a St.Louis favorite on the Hill (The Hill has all the awesome Italian restaurants in town). Your lunch tickets (for those who paid for lunch before midnight of Tuesday 9/11/2012) will be available on your SPEEDPASS. You can take your food and beverages (cans and plastic bottles ONLY) into the classrooms to eat. The Gold sponsors will be presenting 30 minute sessions during lunch in each classroom. Please do stop by their booths and to say hi (such events are not possible without their generous support) and drop your raffle tickets (also on your SPEEDPASS) to enter yourself in drawings for awesome prizes.
There will be plenty of volunteers to help out at the event (look for people wearing blue shirts and wearing lanyards that say “STAFF”). After the last session of the day, we will all assemble in and around room #024 for the closing ceremonies – namely a thank you note and raffle prize drawings ! While we are trying our best to make sure we have taken care of everything, this is our first time organizing an event of this size and we would really appreciate all the help and support we can get to ensure a great event.
The after party will be a small informal gathering of the event attendees at Schlafly Bottleworks, in Maplewood, MO 63143. The SQL Saturday #154 team is only suggesting this venue. Attendees are responsible for their own food and beverages at the after party. SQL Saturday #154 organizers will not be responsible for anything at the after party.
On Friday night (sept 14) around 9.30 PM, we are planning to having a pre-event party in the form of SQL Karaoke. Mike Talayna’s Juke Box Restaurant (1115 Hampton Avenue St. Louis, MO 63139 (314) 647-7600) starts their karaoke at 9.30 PM. All speakers and attendees are welcome to attend (look for kathi Kellenbeger at the event to find the SQL people). The SQL Saturday #154 team is only suggesting this venue. Attendees are responsible for their own food and beverages at this party. SQL Saturday #154 organizers will not be responsible for anything at the party.
We strive to ensure all of you will have a great time at SQL Saturday #154. Please do make the best of the awesome free opportunity to learn and network.
SQL Saturday #122 | Louisville, KY on July 21, 2012 was the 5th SQL Saturday I have attended so far, and my 3rd as a speaker. The St.Louis contingent – Kathi Kellenberger, Kim Tessereau, Mike Lynn, Jay Carter, Cindy Baker and me ! – was especially excited to attend this event, not only because it’s organized by our friend Malathi Mahadevan, but also for a chance to escape the St.Louis heat !
We had almost forgotten about the time zone change when we drove into Louisville at 6 PM Central sharp, only to realize we were an hour late for the speakers’ dinner! The Bristol Bar & Grille was the perfect location for a great speakers’ dinner, and gave us all a chance to relax, network and enjoy some good food (My personal favorite was the Espresso Crème Brûlée).
University of Louisville is a short 10 minute drive from the Marriot Hotel, and thanks to the email notifications with directions, as well as plenty of signs, we had no trouble finding the venue. Thanks to SPEEDPASS, there were no lines at the registration desk and I found they had my favourite Asiago Cheese Bagels for breakfast! My first session for the day was Andy Thiru‘s “SQL Azure Intro and What’s New” session and it surely exceeded my expectations. I have never had the opportunity to work with SQL Azure so far, and this session gave me the knowledge and tools to get me started on my own. The next session on my list was “What Sequence objects are (and are not)” by Louis Davidson. I used to be an Oracle DBA until a few years ago, and took sequences for granted, until I discovered SQL Server doesn’t have them (until 2012). With their introduction in SQL Server 2012, I took this opportunity to get myself reacquainted with Sequences.
I had some delicious Veggie Wraps and a Cookie for lunch – again, no lines and no waiting! Post lunch, I took a break in the Speakers’ Lounge to review my upcoming session on Parameter Sniffing, where I discovered a cooler full of Ice Cream! I had to stop myself after two servings and got back to reviewing my slides & checking my demos. A majority of the attendees for my session were quite involved with the topic, giving rise to several discussions and Q&A, thus making my session all the more valuable for everyone in the room. I was really pleased with the generous evaluations and great feedback for my session.
The last session of the day for me was “Bulletproof: Hardening your SQL Server from Attack” by Sarah Barela. As a developer, I take care of hardening my code against SQL Injection, but usually let administrators worry about securing the servers and databases. This session revealed the amount of work administrators (Database, Server as well as Network) put in to secure our servers ! After the last session, it was time for the closing ceremonies and Raffle. The SQL Saturday #122 Team hosted a great event with a full day of valuable SQL learning. I am really thankful to the SQL Saturday #122 Team for giving me the opportunity to present my session, and the support of all the sponsors to making such events possible.
I am looking forward to see my friends from Louisville again, at SQL Saturday #154 in St.Louis on Sept 15th , the very first SQL Saturday in St.Louis !
While brushing up on my knowledge of software testing concepts, I came across quite an amusing definition of testing; “To tell somebody that he is wrong is called criticism. To do so officially is called testing” . A programmer usually resents it when a tester finds a defect in his code. We programmers thoroughly unit test our code before handing it off to a tester, because we take pride in developing a bug free application. Some programming languages (C# , VB, ASP.NET) afford themselves to be unit testing easily, because the application is developed within Visual Studio and can readily leverage its unit testing framework.
Visual Studio allows you to create Database projects, and database developers have started embracing it since Visual Studio Team Systems 2008 Database Edition GDR. This offers a robust framework for database developers to identify bugs with their database objects (schemas, stored procedures, functions, etc) by unit testing their database (T-SQL) code, before handing it over to the tester. Before we jump into the specifics of database unit testing with Visual Studio, the next couple of paragraphs warm us up to the topic by covering a few basic concepts of software testing.
Software testing, undoubtedly plays a important role in the life cycle of most IT Projects. The Goal of any type of software testing is to identify defects to be fixed, so that the product meets requirements and has a deterministic and predictable output. Depending on the testing method employed, testing can be implemented at any time in the development process. Different software development models will focus the test effort at different phases in the development process. Newer development models, such as Agile, often employ test driven development and place an increased portion of the testing in the hands of the developer, before it reaches a formal team of testers.
Software testing methods are traditionally divided into white and black-box testing. These two approaches are used to describe the point of view that a test engineer takes when designing test cases. Unit Testing falls under the category of white box testing, where the the tester has access to the internal data structures and algorithms, including the code that implements these. This is in contrast with the black-box testing method, which treats the software as a “black box”—without any knowledge of internal implementation. A black box tester is usually not a programmer, and aims to only test the functionality of software according to the applicable requirements. Since the black-box tester has no knowledge on the underlying code, he may find bugs that a programmer misses. However, the same principle can sometimes lead to writing inefficient or incomplete test cases.
Unit Testing is a key component of Test driven development (TDD). Unit Tests are usually written by Developers while they work on the code, to ensure that a specific of piece of code (Function, Class, Stored procedure, etc) is working as expected. Unit Testing helps to identify defects in the earlier stages of the software development life cycle, where they are cheaper to fix. Unit Testing can prove especially challenging in the world of database development, because of the need for a consistent test environment.
Database Unit Tests are used to establish a baseline state for a database and then to verify any subsequent changes that you make to database objects. The Unit Testing Framework in Visual Studio (starting with VSTS 2005) helps database developers create, manage and execute Unit Tests for a Database. The Microsoft.VisualStudio.TestTools.UnitTesting namespace supplies classes that provide unit testing support. This namespace contains many attributes that identify test information to the test engine regarding data sources, order of method execution, program management, agent/host information, and deployment data. It also contains custom unit testing exceptions.
You will need the Database Edition GDR of VSTS 2008 or the Ultimate (or Premium) Editions of VSTS 2010 to create, modify and run database unit tests. You can run database unit tests with Professional Edition on VSTS 2010, but cannot create or modify them. Before you can start running database unit tests in VSTS, you must first create a Database Project and then create a test project. The next step is to write sets of Transact-SQL tests that exercise your database objects. Executing these tests in your isolated development environment helps you to verify whether those objects are behaving correctly before you check them in to version control. As changes are made to the database schema, you can use these tests to verify whether the changes have broken existing functionality. A detailed step by step walk through for creating and running database unit tests can be found here on MSDN . Once Created, a Unit Test Project and of the tests will show up in the Solution Explorer View;
In a typical database unit test, a Transact-SQL test script runs and returns an instance of the ExecutionResult class. The instance of this class contains a DataSet, the execution time, and the rows affected by the script. All of this information is collected during execution of the script. These results can be evaluated within the Transact-SQL script by using the RAISERROR function, or they can be evaluated by using test conditions. Visual Studio Premium provides a set of the following predefined test conditions for you to use;
- Data Checksum
- Empty Resultset
- Execution Time
- Expected Schema
- Not Empty Resultset
- Row Count
- Scalar Value
- Run multiple unit tests as a group
- Run tests as a part of a Build
- Enforce check-in policy
- Software Testing Principles, Terminology & Definitions – http://en.wikipedia.org/wiki/Software_testing
- Unit Testing Framework in Visual Studio –
- Database Unit Testing with Visual Studio –
- Unit Test Conditions in Database Unit Tests – http://msdn.microsoft.com/en-us/library/aa833423
- Test Lists – http://msdn.microsoft.com/en-us/library/ms182461.aspx
- Visual Studio 11 (Beta) Unit Testing updates – http://blogs.msdn.com/b/visualstudioalm/archive/2012/03/08/what-s-new-in-visual-studio-11-beta-unit-testing.aspx
- Software Testing Jokes – http://softwaretestingfundamentals.com/software-testing-jokes/
Service Broker has come a long way since its’ introduction in Microsoft SQL Server 2005. SQL Server 2008 brought a host of Service Broker enhancements like conversation priorities, the ssbdiagnose utility, alternate poison message handling and new performance objects & counters. SQL Server 2012 is a major release that comes with an astonishing array of enhancements and new features, including new bells & whistles for Service Broker.
A significant new feature for Service Broker is the ability to Multicast messages. This enables a single initiator service to send messages to multiple target services, akin to SQL Server Replication, where multiple subscribers can subscribe to the same publication. The syntax of the send command has been extended to enable multicasting , by allowing multiple conversation handles.
DECLARE @cvh1 UNIQUEIDENTIFIER, @cvh2 UNIQUEIDENTIFIER, @cvh3 UNIQUEIDENTIFIER, @TestMsgBody XML ; SET @TestMsgBody = '<test>Test Message</test>' ; BEGIN DIALOG @cvh1 FROM SERVICE [//InitiatorService] TO SERVICE '//TargetService1' ON CONTRACT [//TestProcessing] ; BEGIN DIALOG @cvh2 FROM SERVICE [//InitiatorService] TO SERVICE '//TargetService2' ON CONTRACT [//TestProcessing] ; BEGIN DIALOG @cvh3 FROM SERVICE [//InitiatorService] TO SERVICE '//TargetService3' ON CONTRACT [//TestProcessing] ; SEND ON CONVERSATION (@cvh1, @cvh2, @cvh3) MESSAGE TYPE [//TestMgsType] (@TestMsgBody) ;
Another new feature is the addition of a new column – message_enqueue_time – to the Queues. This column helps us determine the time spent by a message on the queue. The message_enqueue_time column is of datetimeoffset data type and stores the date and time (with time zone awareness) when the message arrives on the queue. Its’ exposed to the application via a direct query on the Queue itself, as well as a column in the Receive statement. Let’s look at an example;
-- Begin dialog & send message DECLARE @ch UNIQUEIDENTIFIER; BEGIN DIALOG CONVERSATION @ch FROM SERVICE [manual_activation_initiator_service] TO SERVICE 'manual_activation_target_service' ON CONTRACT [manual_activation_contract] WITH ENCRYPTION = OFF ; SEND ON CONVERSATION @ch MESSAGE TYPE [manual_activation_demo_request] ('<test>test_message_body</test>'); GO -- A Direct Select statament from the Queue SELECT conversation_handle ,CAST ( message_body AS XML) AS [msg_body] ,DATEDIFF(second,message_enqueue_time,getutcdate()) AS [time_in_queue(Seconds)] FROM [manual_activation_target_queue]; -- Results conversation_handle msg_body time_in_queue(Seconds) ------------------------------------ ------------------------------- ---------------------- C0CB3200-809F-E111-8B29-005056BE0088 <test>test_message_body</test> 21 (1 row(s) affected) -- Retrieve the message off of the Queue with a Receive WAITFOR ( RECEIVE TOP(1) conversation_handle ,CAST(message_body AS XML) AS [msg_body] ,DATEDIFF(second,message_enqueue_time,getutcdate()) AS [time_in_queue(Seconds)] FROM manual_activation_target_queue), TIMEOUT 5; -- Results conversation_handle msg_body time_in_queue(Seconds) ------------------------------------ ------------------------------- ---------------------- C0CB3200-809F-E111-8B29-005056BE0088 <test>test_message_body</test> 21 (1 row(s) affected)
Please note that this column is not well documented yet and to derive the time spent by a message on the queue in seconds, one must use a few date & time functions.
Service Broker Remote Messaging needs some additional configuration in order to get along with the Always On Availability Groups, due to the complexity added by the Listener for an Availability group. The Always On Availability Groups feature introduced in SQL Server 2012, is a high availability and disaster recovery solution that provides an enterprise level alternative to database mirroring.
For a Service in an Availability Group to be able to Receive remote messages;
- The Availability Group must have a listener configured
- Service Broker Endpoint must be created and configured with the Listener, for every instance of SQL Server in the Availability Group
- Connect permissions must be granted on the endpoints to the the appropriate login(s)
- msdb must contain a route
For a Service in an Availability Group to be able to Send messages to a remote service;
- Configure a route to the target service using the listener
- msdb must contain a route
And last but not the least, its always worth mentioning that since SQL Server 2008 R2, Poison message handling can be disabled at the time of queue creation or at a later time by using the alter queue statement. You can also check the status of poison message handling for each queue, by querying the sys.service_queues catalog view, which has the column, is_poison_message_handling_enabled to indicate whether poison message is enabled or disabled.