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  • SQLAuthority News – Book Review – Beginning T-SQL 2008 by Kathi Kellenberger

    - by pinaldave
    Beginning T-SQL 2008 by Kathi Kellenberger Amazon Link Detail Review: Beginning T-SQL 2008 is one of the best books on the market if you are just beginning to work with Microsoft SQL, or have a little bit of experience and need to learn more quickly. Each chapter of the book introduces a new subject, and builds upon topics covered in previous chapters.  The author of the book, Kathi Kellenberger understands that you need to form a solid foundation of knowledge before moving on to new topics, and sets up each subject nicely.  Because the chapters move in an orderly progression, you continue to use skills you learned earlier. One of the best features of Beginning T-SQL 2008 is that each chapter has multiple examples and exercises.  Many books introduce a topic and then never go back to it.  This book gives enough examples that you will be familiar with the subject when you come across it in real life.  The exercises at the end of the chapter mean that you will be using the skills you learned – and there is no better way to cement a subject in your brain. The book also includes discussions of the common errors that programmers will come across, how to avoid them, and how to fix them if they happen.  Ms. Kellenberger understands that not only do mistakes happen, but they are bound to happen if you aren’t trained properly.  Mistakes are part of the learning process! The book begins by discussions relational theory, so that programmers will understand the way T-SQL works from the ground up.  It also walks readers through writing accurate queries, combining set-based and procedural processing, embedding logic in stored functions, and so much more. Overall, the main goal of Beginning T-SQL 2008 is to introduce novices to SQL programming, and quickly familiarize them with the basics of running the program.  The book is written with the idea that readers will not know any of the technical terms or vocabulary.  However, if you are a little more familiar with SQL and looking to become better, you will still find this book very helpful. Ratting: 4.5+ Stars Summary: I must recommend Beginning T-SQL 2008 highly enough.  If you are going to buy any beginners guide to Transect-SQL, this is the one you should spend your money on.  You can save yourself a lot of time and effort later by using this very affordable manual to learn the basics, which will allow you to become an expert much faster. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority Book Review, SQLAuthority News, T SQL, Technology

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  • SQL SERVER – Index Created on View not Used Often – Observation of the View

    - by pinaldave
    I always enjoy writing about concepts on Views. Views are frequently used concepts, and so it’s not surprising that I have seen so many misconceptions about this subject. To clear such misconceptions, I have previously written the article SQL SERVER – The Limitations of the Views – Eleven and more…. I also wrote a follow up article wherein I demonstrated that without even creating index on the basic table, the query on the View will not use the View. You can read about this demonstration over here: SQL SERVER – Index Created on View not Used Often – Limitation of the View 12. I promised in that post that I would also write an article where I would demonstrate the condition where the Index will be used. I got many responses suggesting that I can do that with using NOEXPAND; I agree. I have already written about this in my original summary article. Here is a way for you to see how Index created on View can be utilized. We will do the following steps on this exercise: Create a Table Create a View Create Index On View Write SELECT with ORDER BY on View USE tempdb GO IF EXISTS (SELECT * FROM sys.views WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[SampleView]')) DROP VIEW [dbo].[SampleView] GO IF EXISTS (SELECT * FROM sys.objects WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[mySampleTable]') AND TYPE IN (N'U')) DROP TABLE [dbo].[mySampleTable] GO -- Create SampleTable CREATE TABLE mySampleTable (ID1 INT, ID2 INT, SomeData VARCHAR(100)) INSERT INTO mySampleTable (ID1,ID2,SomeData) SELECT TOP 100000 ROW_NUMBER() OVER (ORDER BY o1.name), ROW_NUMBER() OVER (ORDER BY o2.name), o2.name FROM sys.all_objects o1 CROSS JOIN sys.all_objects o2 GO -- Create View CREATE VIEW SampleView WITH SCHEMABINDING AS SELECT ID1,ID2,SomeData FROM dbo.mySampleTable GO -- Create Index on View CREATE UNIQUE CLUSTERED INDEX [IX_ViewSample] ON [dbo].[SampleView] ( ID2 ASC ) GO -- Select from view SELECT ID1,ID2,SomeData FROM SampleView ORDER BY ID2 GO When we check the execution plan for this , we find it clearly that the Index created on the View is utilized. ORDER BY clause uses the Index created on the View. I hope this makes the puzzle simpler on how the Index is used on the View. Again, I strongly recommend reading my earlier series about the limitations of the Views found here: SQL SERVER – The Limitations of the Views – Eleven and more…. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL View, T SQL, Technology

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  • SQL SERVER – Challenge – Puzzle – Usage of FAST Hint

    - by pinaldave
    I was recently working with various SQL Server Hints. After working for a day on various hints, I realize that for one hint, I am not able to come up with good example. The hint is FAST. Let us look at the definition of the FAST hint from the Book On-Line. FAST number_rows Specifies that the query is optimized for fast retrieval of the first number_rows. This is a nonnegative integer. After the first number_rows are returned, the query continues execution and produces its full result set. Now the question is in what condition this hint can be useful. I have tried so many different combination, I have found this hint does not make much performance difference, infect I did not notice any change in time taken to load the resultset. I noticed that this hint does not change number of the page read to return result. Now when there is difference in performance is expected because if you read the what FAST hint does is that it only returns first few results FAST – which does not mean there will be difference in performance. I also understand that this hint gives the guidance/suggestions/hint to query optimizer that there are only 100 rows are in expected resultset. This tricking the optimizer to think there are only 100 rows and which (may) lead to render different execution plan than the one which it would have taken in normal case (without hint). Again, not necessarily, this will happen always. Now if you read above discussion, you will find that basic understanding of the hint is very clear to me but I still feel that I am missing something. Here are my questions: 1) In what condition this hint can be useful? What is the case, when someone want to see first few rows early because my experience suggests that when first few rows are rendered remaining rows are rendered as well. 2) Is there any way application can retrieve the fast fetched rows from SQL Server? 3) Do you use this hint in your application? Why? When? and How? Here are few examples I have attempted during the my experiment and found there is no difference in execution plan except its estimated number of rows are different leading optimizer think that the cost is less but in reality that is not the case. USE AdventureWorks GO SET STATISTICS IO ON SET STATISTICS TIME ON GO --------------------------------------------- -- Table Scan with Fast Hint SELECT * FROM Sales.SalesOrderDetail GO SELECT * FROM Sales.SalesOrderDetail OPTION (FAST 100) GO --------------------------------------------- -- Table Scan with Where on Index Key SELECT * FROM Sales.SalesOrderDetail WHERE OrderQty = 14 GO SELECT * FROM Sales.SalesOrderDetail WHERE OrderQty = 14 OPTION (FAST 100) GO --------------------------------------------- -- Table Scan with Where on Index Key SELECT * FROM Sales.SalesOrderDetail WHERE SalesOrderDetailID < 1000 GO SELECT * FROM Sales.SalesOrderDetail WHERE SalesOrderDetailID < 1000 OPTION (FAST 100) GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Dedicated Access Control for SQL Server Express Edition – An error occurred while obtaining the dedicated administrator connection (DAC) port.

    - by pinaldave
    Recently I had faced very interesting situation. Due to some reason we were not able to login into the production server for one of client. The reason for the same was that server was very busy, we had to login into the system and bring server to normal situation. When all the attempts failed, I decided to login using Dedicated Administrator Connection (DAC). However when I attempted to connect using DAC it threw following error for me. C:\Users\pinald>sqlcmd -A -d master -S .\SQLEXPRESS Sqlcmd: Error: Microsoft SQL Server Native Client 11.0 : SQL Server Network Interfaces: An error occurred while obtaining the dedicated administrator connection (DAC) port. Make sure that SQL Browser is running, or check the error log for t he port number [xFFFFFFFF]. .Sqlcmd: Error: Microsoft SQL Server Native Client 11.0 : Login timeout expired.Sqlcmd: Error: Microsoft SQL Server Native Client 11.0 : A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online. I was bit taken a back as I knew that my commands are correct to login and if DAC does not work, there should be some serious reason for it. When inquired further about the SQL Server version I learned that it was SQL Server Express version deployed. To conserve resources, SQL Server Express does not listen on the DAC port. There is an additional step to be done if SQL Server Express has to be used with DAC. Enable TRACEFLAG on SQL Server Express will enable the connection by DAC possible. Here is the quick methods how one can enable DAC on SQL Server Express. Go to Start >> All Program >>Microsoft SQL Server (your version) >> Configuration Tools >> SQL Server Configuration Manager. Click on SQL Server Services >> Select your SQL Server Express version >> Right Click Properties >> select Startup Parameters Once on the Startup Parameter add the Startup parameter which is TRACEFLAG -T7806. Click on OK and RESTART SQL Server Express edition. Now once again try to connect to SQL Server Express edition and it will work just fine. This is absolutely documented method on BOL and SQL Server Express needs to be restarted. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Error Messages, SQL Interview Questions and Answers, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology Tagged: SQL Server Express

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  • SQL SERVER – Log File Growing for Model Database – model Database Log File Grew Too Big

    - by pinaldave
    After reading my earlier article SQL SERVER – master Database Log File Grew Too Big, I received an email recently from another reader asking why does the log file of model database grow every day when he is not carrying out any operation in the model database. As per the email, he is absolutely sure that he is doing nothing on his model database; he had used policy management to catch any T-SQL operation in the model database and there were none. This was indeed surprising to me. I sent a request to access to his server, which he happily agreed for and within a min, we figured out the issue. He was taking the backup of the model database every day taking the database backup every night. When I explained the same to him, he did not believe it; so I quickly wrote down the following script. The results before and after the usage of the script were very clear. What is a model database? The model database is used as the template for all databases created on an instance of SQL Server. Any object you create in the model database will be automatically created in subsequent user database created on the server. NOTE: Do not run this in production environment. During the demo, the model database was in full recovery mode and only full backup operation was performed (no log backup). Before Backup Script Backup Script in loop DECLARE @FLAG INT SET @FLAG = 1 WHILE(@FLAG < 1000) BEGIN BACKUP DATABASE [model] TO  DISK = N'D:\model.bak' SET @FLAG = @FLAG + 1 END GO After Backup Script Why did this happen? The model database was in full recovery mode and taking full backup is logged operation. As there was no log backup and only full backup was performed on the model database, the size of the log file kept growing. Resolution: Change the backup mode of model database from “Full Recovery” to “Simple Recovery.”. Take full backup of the model database “only” when you change something in the model database. Let me know if you have encountered a situation like this? If so, how did you resolve it? It will be interesting to know about your experience. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Automation Process Good or Ugly

    - by pinaldave
    This blog post is written in response to T-SQL Tuesday hosted by SQL Server Insane Asylum. The idea of this post really caught my attention. Automation – something getting itself done after the initial programming, is my understanding of the subject. The very next thought was – is it good or evil? The reality is there is no right answer. However, what if we quickly note a few things, then I would like to request your help to complete this post. We will start with the positive parts in SQL Server where automation happens. The Good If I start thinking of SQL Server and Automation the very first thing that comes to my mind is SQL Agent, which runs various jobs. Once I configure any task or job, it runs fine (till something goes wrong!). Well, automation has its own advantages. We all have used SQL Agent for so many things – backup, various validation jobs, maintenance jobs and numerous other things. What other kinds of automation tasks do you run in your database server? The Ugly This part is very interesting, because it can get really ugly(!). During my career I have found so many bad automation agent jobs. Client had an agent job where he was dropping the clean buffers every hour Client using database mail to send regular emails instead of necessary alert related emails The best one – A client used new Missing Index and Unused Index scripts in SQL Agent Job to follow suggestions 100%. Believe me, I have never seen such a badly performing and hard to optimize database. (I ended up dropping all non-clustered indexes on the development server and ran production workload on the development server again, then configured with optimal indexes). Shrinking database is performance killer. It should never be automated. SQL SERVER – Shrinking Database is Bad – Increases Fragmentation – Reduces Performance The one I hate the most is AutoShrink Database. It has given me hard time in my career quite a few times. SQL SERVER – SHRINKDATABASE For Every Database in the SQL Server Automation is necessary but common sense is a must when creating automation. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – PREEMPTIVE and Non-PREEMPTIVE – Wait Type – Day 19 of 28

    - by pinaldave
    In this blog post, we are going to talk about a very interesting subject. I often get questions related to SQL Server 2008 Book-Online about various Preemptive wait types. I got a few questions asking what these wait types are and how they could be interpreted. To get current wait types of the system, you can read this article and run the script: SQL SERVER – DMV – sys.dm_os_waiting_tasks and sys.dm_exec_requests – Wait Type – Day 4 of 28. Before we continue understanding them, let us study first what PREEMPTIVE and Non-PREEMPTIVE waits in SQL Server mean. PREEMPTIVE: Simply put, this wait means non-cooperative. While SQL Server is executing a task, the Operating System (OS) interrupts it. This leads to SQL Server to involuntarily give up the execution for other higher priority tasks. This is not good for SQL Server as it is a particular external process which makes SQL Server to yield. This kind of wait can reduce the performance drastically and needs to be investigated properly. Non-PREEMPTIVE: In simple terms, this wait means cooperative. SQL Server manages the scheduling of the threads. When SQL Server manages the scheduling instead of the OS, it makes sure its own priority. In this case, SQL Server decides the priority and one thread yields to another thread voluntarily. In the earlier version of SQL Server, there was no preemptive wait types mentioned and the associated task status with them was marked as suspended. In SQL Server 2005, preemptive wait types were not listed as well, but their associated task status was marked as running. In SQL Server 2008, preemptive wait types are properly listed and their associated task status is also marked as running. Now, SQL Server is in Non-Preemptive mode by default and it works fine. When CLR, extended Stored Procedures and other external components run, they run in Preemptive mode, leading to the creation of these wait types. There are a wide variety of preemptive wait types. If you see consistent high value in the Preemptive wait types, I strongly suggest that you look into the wait type and try to know the root cause. If you are still not sure, you can send me an email or leave a comment about it and I will do my best to help you reduce this wait type. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – DMV – sys.dm_exec_query_optimizer_info – Statistics of Optimizer

    - by pinaldave
    Incredibly, SQL Server has so much information to share with us. Every single day, I am amazed with this SQL Server technology. Sometimes I find several interesting information by just querying few of the DMV. And when I present this info in front of my client during performance tuning consultancy, they are surprised with my findings. Today, I am going to share one of the hidden gems of DMV with you, the one which I frequently use to understand what’s going on under the hood of SQL Server. SQL Server keeps the record of most of the operations of the Query Optimizer. We can learn many interesting details about the optimizer which can be utilized to improve the performance of server. SELECT * FROM sys.dm_exec_query_optimizer_info WHERE counter IN ('optimizations', 'elapsed time','final cost', 'insert stmt','delete stmt','update stmt', 'merge stmt','contains subquery','tables', 'hints','order hint','join hint', 'view reference','remote query','maximum DOP', 'maximum recursion level','indexed views loaded', 'indexed views matched','indexed views used', 'indexed views updated','dynamic cursor request', 'fast forward cursor request') All occurrence values are cumulative and are set to 0 at system restart. All values for value fields are set to NULL at system restart. I have removed a few of the internal counters from the script above, and kept only documented details. Let us check the result of the above query. As you can see, there is so much vital information that is revealed in above query. I can easily say so many things about how many times Optimizer was triggered and what the average time taken by it to optimize my queries was. Additionally, I can also determine how many times update, insert or delete statements were optimized. I was able to quickly figure out that my client was overusing the Query Hints using this dynamic management view. If you have been reading my blog, I am sure you are aware of my series related to SQL Server Views SQL SERVER – The Limitations of the Views – Eleven and more…. With this, I can take a quick look and figure out how many times Views were used in various solutions within the query. Moreover, you can easily know what fraction of the optimizations has been involved in tuning server. For example, the following query would tell me, in total optimizations, what the fraction of time View was “reference“. As this View also includes system Views and DMVs, the number is a bit higher on my machine. SELECT (SELECT CAST (occurrence AS FLOAT) FROM sys.dm_exec_query_optimizer_info WHERE counter = 'view reference') / (SELECT CAST (occurrence AS FLOAT) FROM sys.dm_exec_query_optimizer_info WHERE counter = 'optimizations') AS ViewReferencedFraction Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – DMV – sys.dm_os_waiting_tasks and sys.dm_exec_requests – Wait Type – Day 4 of 28

    - by pinaldave
    Previously, we covered the DMV sys.dm_os_wait_stats, and also saw how it can be useful to identify the major resource bottleneck. However, at the same time, we discussed that this is only useful when we are looking at an instance-level picture. Quite often we want to know about the processes going in our server at the given instant. Here is the query for the same. This DMV is written taking the following into consideration: we want to analyze the queries that are currently running or which have recently ran and their plan is still in the cache. SELECT dm_ws.wait_duration_ms, dm_ws.wait_type, dm_es.status, dm_t.TEXT, dm_qp.query_plan, dm_ws.session_ID, dm_es.cpu_time, dm_es.memory_usage, dm_es.logical_reads, dm_es.total_elapsed_time, dm_es.program_name, DB_NAME(dm_r.database_id) DatabaseName, -- Optional columns dm_ws.blocking_session_id, dm_r.wait_resource, dm_es.login_name, dm_r.command, dm_r.last_wait_type FROM sys.dm_os_waiting_tasks dm_ws INNER JOIN sys.dm_exec_requests dm_r ON dm_ws.session_id = dm_r.session_id INNER JOIN sys.dm_exec_sessions dm_es ON dm_es.session_id = dm_r.session_id CROSS APPLY sys.dm_exec_sql_text (dm_r.sql_handle) dm_t CROSS APPLY sys.dm_exec_query_plan (dm_r.plan_handle) dm_qp WHERE dm_es.is_user_process = 1 GO You can change CROSS APPLY to OUTER APPLY if you want to see all the details which are omitted because of the plan cache. Let us analyze the result of the above query and see how it can be helpful to identify the query and the kind of wait type it creates. Click to Enlarage The above query will return various columns. There are various columns that provide very important details. e.g. wait_duration_ms – it indicates current wait for the query that executes at that point of time. wait_type – it indicates the current wait type for the query text – indicates the query text query_plan – when clicked on the same, it will display the query plans There are many other important information like CPU_time, memory_usage, and logical_reads, which can be read from the query as well. In future posts on this series, we will see how once identified wait type we can attempt to reduce the same. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: DMV, Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – Puzzle to Win Print Book – Explain Value of PERCENTILE_CONT() Using Simple Example

    - by pinaldave
    From last several days I am working on various Denali Analytical functions and it is indeed really fun to refresh the concept which I studied in the school. Earlier I wrote article where I explained how we can use PERCENTILE_CONT() to find median over here SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012. Today I am going to ask question based on the same blog post. Again just like last time the intention of this puzzle is as following: Learn new concept of SQL Server 2012 Learn new concept of SQL Server 2012 even if you are on earlier version of SQL Server. On another note, SQL Server 2012 RC0 has been announced and available to download SQL SERVER – 2012 RC0 Various Resources and Downloads. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: The reason we get median is because we are passing value .05 to PERCENTILE_COUNT() function. Now run read the puzzle. Puzzle: Run following T-SQL code: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.9) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO Observe the result and you will notice that MidianCont has different value than before, the reason is PERCENTILE_CONT function has 0.9 value passed. For first four value the value is 775.1. Now run following T-SQL code: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.1) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO Observe the result and you will notice that MidianCont has different value than before, the reason is PERCENTILE_CONT function has 0.1 value passed. For first four value the value is 709.3. Now in my example I have explained how the median is found using this function. You have to explain using mathematics and explain (in easy words) why the value in last columns are 709.3 and 775.1 Hint: SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012 Rules Leave a comment with your detailed answer by Nov 25's blog post. Open world-wide (where Amazon ships books) If you blog about puzzle’s solution and if you win, you win additional surprise gift as well. Prizes Print copy of my new book SQL Server Interview Questions Amazon|Flipkart If you already have this book, you can opt for any of my other books SQL Wait Stats [Amazon|Flipkart|Kindle] and SQL Programming [Amazon|Flipkart|Kindle]. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Display Datetime in Specific Format – SQL in Sixty Seconds #033 – Video

    - by pinaldave
    A very common requirement of developers is to format datetime to their specific need. Every geographic location has different need of the date formats. Some countries follow the standard of mm/dd/yy and some countries as dd/mm/yy. The need of developer changes as geographic location changes. In SQL Server there are various functions to aid this requirement. There is function CAST, which developers have been using for a long time as well function CONVERT which is a more enhanced version of CAST. In the latest version of SQL Server 2012 a new function FORMAT is introduced as well. In this SQL in Sixty Seconds video we cover two different methods to display the datetime in specific format. 1) CONVERT function and 2) FORMAT function. Let me know what you think of this video. Here is the script which is used in the video: -- http://blog.SQLAuthority.com -- SQL Server 2000/2005/2008/2012 onwards -- Datetime SELECT CONVERT(VARCHAR(30),GETDATE()) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),10) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),110) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),5) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),105) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),113) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),114) AS DateConvert; GO -- SQL Server 2012 onwards -- Various format of Datetime SELECT CONVERT(VARCHAR(30),GETDATE(),113) AS DateConvert; SELECT FORMAT ( GETDATE(), 'dd mon yyyy HH:m:ss:mmm', 'en-US' ) AS DateConvert; SELECT CONVERT(VARCHAR(30),GETDATE(),114) AS DateConvert; SELECT FORMAT ( GETDATE(), 'HH:m:ss:mmm', 'en-US' ) AS DateConvert; GO -- Specific usage of Format function SELECT FORMAT(GETDATE(), N'"Current Time is "dddd MMMM dd, yyyy', 'en-US') AS CurrentTimeString; This video discusses CONVERT and FORMAT in simple manner but the subject is much deeper and there are lots of information to cover along with it. I strongly suggest that you go over related blog posts in next section as there are wealth of knowledge discussed there. Related Tips in SQL in Sixty Seconds: Get Date and Time From Current DateTime – SQL in Sixty Seconds #025 Retrieve – Select Only Date Part From DateTime – Best Practice Get Time in Hour:Minute Format from a Datetime – Get Date Part Only from Datetime DATE and TIME in SQL Server 2008 Function to Round Up Time to Nearest Minutes Interval Get Date Time in Any Format – UDF – User Defined Functions Retrieve – Select Only Date Part From DateTime – Best Practice – Part 2 Difference Between DATETIME and DATETIME2 Saturday Fun Puzzle with SQL Server DATETIME2 and CAST What would you like to see in the next SQL in Sixty Seconds video? Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Excel

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  • SQL SERVER – Select and Delete Duplicate Records – SQL in Sixty Seconds #036 – Video

    - by pinaldave
    Developers often face situations when they find their column have duplicate records and they want to delete it. A good developer will never delete any data without observing it and making sure that what is being deleted is the absolutely fine to delete. Before deleting duplicate data, one should select it and see if the data is really duplicate. In this video we are demonstrating two scripts – 1) selects duplicate records 2) deletes duplicate records. We are assuming that the table has a unique incremental id. Additionally, we are assuming that in the case of the duplicate records we would like to keep the latest record. If there is really a business need to keep unique records, one should consider to create a unique index on the column. Unique index will prevent users entering duplicate data into the table from the beginning. This should be the best solution. However, deleting duplicate data is also a very valid request. If user realizes that they need to keep only unique records in the column and if they are willing to create unique constraint, the very first requirement of creating a unique constraint is to delete the duplicate records. Let us see how to connect the values in Sixty Seconds: Here is the script which is used in the video. USE tempdb GO CREATE TABLE TestTable (ID INT, NameCol VARCHAR(100)) GO INSERT INTO TestTable (ID, NameCol) SELECT 1, 'First' UNION ALL SELECT 2, 'Second' UNION ALL SELECT 3, 'Second' UNION ALL SELECT 4, 'Second' UNION ALL SELECT 5, 'Second' UNION ALL SELECT 6, 'Third' GO -- Selecting Data SELECT * FROM TestTable GO -- Detecting Duplicate SELECT NameCol, COUNT(*) TotalCount FROM TestTable GROUP BY NameCol HAVING COUNT(*) > 1 ORDER BY COUNT(*) DESC GO -- Deleting Duplicate DELETE FROM TestTable WHERE ID NOT IN ( SELECT MAX(ID) FROM TestTable GROUP BY NameCol) GO -- Selecting Data SELECT * FROM TestTable GO DROP TABLE TestTable GO Related Tips in SQL in Sixty Seconds: SQL SERVER – Delete Duplicate Records – Rows SQL SERVER – Count Duplicate Records – Rows SQL SERVER – 2005 – 2008 – Delete Duplicate Rows Delete Duplicate Records – Rows – Readers Contribution Unique Nonclustered Index Creation with IGNORE_DUP_KEY = ON – A Transactional Behavior What would you like to see in the next SQL in Sixty Seconds video? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Excel

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  • SQL SERVER – Rename Columnname or Tablename – SQL in Sixty Seconds #032 – Video

    - by pinaldave
    We all make mistakes at some point of time and we all change our opinion. There are quite a lot of people in the world who have changed their name after they have grown up. Some corrected their parent’s mistake and some create new mistake. Well, databases are not protected from such incidents. There are many reasons why developers may want to change the name of the column or table after it was initially created. The goal of this video is not to dwell on the reasons but to learn how we can rename the column and table. Earlier I have written the article on this subject over here: SQL SERVER – How to Rename a Column Name or Table Name. I have revised the same article over here and created this video. There is one very important point to remember that by changing the column name or table name one creates the possibility of errors in the application the columns and tables are used. When any column or table name is changed, the developer should go through every place in the code base, ad-hoc queries, stored procedures, views and any other place where there are possibility of their usage and change them to the new name. If this is one followed up religiously there are quite a lot of changes that application will stop working due to this name change.  One has to remember that changing column name does not change the name of the indexes, constraints etc and they will continue to reference the old name. Though this will not stop the show but will create visual un-comfort as well confusion in many cases. Here is my question back to you – have you changed ever column name or table name in production database (after project going live)? If yes, what was the scenario and need of doing it. After all it is just a name. Let me know what you think of this video. Here is the updated script. USE tempdb GO CREATE TABLE TestTable (ID INT, OldName VARCHAR(20)) GO INSERT INTO TestTable VALUES (1, 'First') GO -- Check the Tabledata SELECT * FROM TestTable GO -- Rename the ColumnName sp_RENAME 'TestTable.OldName', 'NewName', 'Column' GO -- Check the Tabledata SELECT * FROM TestTable GO -- Rename the TableName sp_RENAME 'TestTable', 'NewTable' GO -- Check the Tabledata - Error SELECT * FROM TestTable GO -- Check the Tabledata - New SELECT * FROM NewTable GO -- Cleanup DROP TABLE NewTable GO Related Tips in SQL in Sixty Seconds: SQL SERVER – How to Rename a Column Name or Table Name What would you like to see in the next SQL in Sixty Seconds video? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Excel

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  • SQL SERVER – 2011 – Introduction to SEQUENCE – Simple Example of SEQUENCE

    - by pinaldave
    SQL Server 2011 will contain one of the very interesting feature called SEQUENCE. I have waited for this feature for really long time. I am glad it is here finally. SEQUENCE allows you to define a single point of repository where SQL Server will maintain in memory counter. USE AdventureWorks2008R2 GO CREATE SEQUENCE [Seq] AS [int] START WITH 1 INCREMENT BY 1 MAXVALUE 20000 GO SEQUENCE is very interesting concept and I will write few blog post on this subject in future. Today we will see only working example of the same. Let us create a sequence. We can specify various values like start value, increment value as well maxvalue. -- First Run SELECT NEXT VALUE FOR Seq, c.CustomerID FROM Sales.Customer c GO -- Second Run SELECT NEXT VALUE FOR Seq, c.AccountNumber FROM Sales.Customer c GO Once the sequence is defined, it can be fetched using following method. Every single time new incremental value is provided, irrespective of sessions. Sequence will generate values till the max value specified. Once the max value is reached, query will stop and will return error message. Msg 11728, Level 16, State 1, Line 2 The sequence object ‘Seq’ has reached its minimum or maximum value. Restart the sequence object to allow new values to be generated. We can restart the sequence from any particular value and it will work fine. -- Restart the Sequence ALTER SEQUENCE [Seq] RESTART WITH 1 GO -- Sequence Restarted SELECT NEXT VALUE FOR Seq, c.CustomerID FROM Sales.Customer c GO Let us do final clean up. -- Clean Up DROP SEQUENCE [Seq] GO There are lots of things one can find useful about this feature. We will see that in future posts. Here is the complete code for easy reference. USE AdventureWorks2008R2 GO CREATE SEQUENCE [Seq] AS [int] START WITH 1 INCREMENT BY 1 MAXVALUE 20000 GO -- First Run SELECT NEXT VALUE FOR Seq, c.CustomerID FROM Sales.Customer c GO -- Second Run SELECT NEXT VALUE FOR Seq, c.AccountNumber FROM Sales.Customer c GO -- Restart the Sequence ALTER SEQUENCE [Seq] RESTART WITH 1 GO -- Sequence Restarted SELECT NEXT VALUE FOR Seq, c.CustomerID FROM Sales.Customer c GO -- Clean Up DROP SEQUENCE [Seq] GO Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – LOGBUFFER – Wait Type – Day 18 of 28

    - by pinaldave
    At first, I was not planning to write about this wait type. The reason was simple- I have faced this only once in my lifetime so far maybe because it is one of the top 5 wait types. I am not sure if it is a common wait type or not, but in the samples I had it really looks rare to me. From Book On-Line: LOGBUFFER Occurs when a task is waiting for space in the log buffer to store a log record. Consistently high values may indicate that the log devices cannot keep up with the amount of log being generated by the server. LOGBUFFER Explanation: The book online definition of the LOGBUFFER seems to be very accurate. On the system where I faced this wait type, the log file (LDF) was put on the local disk, and the data files (MDF, NDF) were put on SanDrives. My client then was not familiar about how the file distribution was supposed to be. Once we moved the LDF to a faster drive, this wait type disappeared. Reducing LOGBUFFER wait: There are several suggestions to reduce this wait stats: Move Transaction Log to Separate Disk from mdf and other files. (Make sure your drive where your LDF is has no IO bottleneck issues). Avoid cursor-like coding methodology and frequent commit statements. Find the most-active file based on IO stall time, as shown in the script written over here. You can also use fn_virtualfilestats to find IO-related issues using the script mentioned over here. Check the IO-related counters (PhysicalDisk:Avg.Disk Queue Length, PhysicalDisk:Disk Read Bytes/sec and PhysicalDisk :Disk Write Bytes/sec) for additional details. Read about them over here. If you have noticed, my suggestions for reducing the LOGBUFFER is very similar to WRITELOG. Although the procedures on reducing them are alike, I am not suggesting that LOGBUFFER and WRITELOG are same wait types. From the definition of the two, you will find their difference. However, they are both related to LOG and both of them can severely degrade the performance. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – Tricks to Replace SELECT * with Column Names – SQL in Sixty Seconds #017 – Video

    - by pinaldave
    You might have heard many times that one should not use SELECT * as there are many disadvantages to the usage of the SELECT *. I also believe that there are always rare occasion when we need every single column of the query. In most of the cases, we only need a few columns of the query and we should retrieve only those columns. SELECT * has many disadvantages. Let me list a few and remaining you can add as a comment.  Retrieves unnecessary columns and increases network traffic When a new columns are added views needs to be refreshed manually Leads to usage of sub-optimal execution plan Uses clustered index in most of the cases instead of using optimal index It is difficult to debug. There are two quick tricks I have discussed in the video which explains how users can avoid using SELECT * but instead list the column names. 1) Drag the columns folder from SQL Server Management Studio to Query Editor 2) Right Click on Table Name >> Script TAble AS >> SELECT To… >> Select option It is extremely easy to list the column names in the table. In today’s sixty seconds video, you will notice that I was able to demonstrate both the methods very quickly. From now onwards there should be no excuse for not listing ColumnName. Let me ask a question back – is there ever a reason to SELECT *? If yes, would you please share that as a comment. More on SELECT *: SQL SERVER – Solution – Puzzle – SELECT * vs SELECT COUNT(*) SQL SERVER – Puzzle – SELECT * vs SELECT COUNT(*) SQL SERVER – SELECT vs. SET Performance Comparison I encourage you to submit your ideas for SQL in Sixty Seconds. We will try to accommodate as many as we can. If we like your idea we promise to share with you educational material. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video

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  • SQLAuthority News – Online Webcast How to Identify Resource Bottlenecks – Wait Types and Queues

    - by pinaldave
    As all of you know I have been working a recently on the subject SQL Server Wait Statistics, the reason is since I have published book on this subject SQL Wait Stats Joes 2 Pros: SQL Performance Tuning Techniques Using Wait Statistics, Types & Queues [Amazon] | [Flipkart] | [Kindle], lots of question and answers I am encountering. When I was writing the book, I kept version 1 of the book in front of me. I wanted to write something which one can use right away. I wanted to create an primer for everybody who have not explored wait stats method of performance tuning. Well, the books have been very well received and in fact we ran out of huge stock 2 times in India so far and once in USA during SQLPASS. I have received so many questions on this subject that I feel I can write one more book of the same size. I have been asked if I can create videos which can go along with this book. Personally I am working with SQL Server 2012 CTP3 and there are so many new wait types, I feel the subject of wait stats is going to be very very crucial in next version of SQL Server. If you have not started learning about this subject, I suggest you at least start exploring this right now. Learn how to begin on this subject atleast as when the next version comes in, you know how to read DMVs. I will be presenting on the same subject of performance tuning by wait stats in webcast embarcadero SQL Server Community Webinar. Here are few topics which we will be covering during the webinar. Beginning with SQL Wait Stats Understanding various aspect of SQL Wait Stats Understanding Query Life Cycle Identifying three TOP wait Stats Resolution of the common 3 wait types and queues Details of the webcast: How to Identify Resource Bottlenecks – Wait Types and Queues Date and Time: Wednesday, November 2, 11:00 AM PDT Registration Link I thank embarcadero for organizing opportunity for me to share my experience on subject of wait stats and connecting me with community to further take this subject to next level. One more interesting thing, I will ask one question at the end of the webinar and I will be giving away 5 copy of my SQL Wait Stats print book to first five correct answers. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – SSMS 2012 Reset Keyboard Shortcuts to Default

    - by pinaldave
    As a technologist, I love my laptop very much and I do not lend it to anyone as I am usually worried that my settings would be messed up when I get it back from its borrower. Honestly, I love how I have set up my laptop and I enjoy the settings and programs I have placed on my computer. If someone changes things there – it will surely be annoying for me. Recently at one of the conferences I was attending in, a small accident happened – one of the speaker’s hard drives failed. The owner immediately panicked due to this and had no clue what to do. I suggested that he may not be able to show the demos but can still show a few things with the product. He accepted my suggestion and finished the presentation. Good thing everybody looked satisfied. Little did I know that a small accident was waiting for me later that day. When I opened my SQL Server Denali, all my shortcuts were totally out of order. When I hit F5, instead of executing query, it was opening up some debugging screen for me. I was very much annoyed so I decided to surf the Internet for me to know how I could reset it to SQL Server 2012 default shortcut. There were so many different advices which further confused me. After reading 4-5 different methods, I used the following method to reset my SQL Server 2012 keyboard shortcuts: Go to SSMS > Tools >> Import and Export Settings… As I wanted to reset all the settings I selected the “Reset all settings” option, but you can select other options as per your need. I suggest you save your current Settings; however, in my case, I did not like the current option so I just decided to overwrite my settings. Here I have two options –  I can either set my shortcut to SQL Server 2012 settings or Visual Studio 2010. I went ahead with the SQL Server 2012 option. Success! Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – DVM sys.dm_os_sys_info Column Name Changed in SQL Server 2012

    - by pinaldave
    Have you ever faced situation where something does not work and when you try to go and fix it – you like fixing it and started to appreciate the breaking changes. Well, this is exactly I felt yesterday. Before I begin my story of yesterday I want to state it candidly that I do not encourage anybody to use * in the SELECT statement. One of the my DBA friend who always used my performance tuning script yesterday sent me email asking following question - “Every time I want to retrieve OS related information in SQL Server – I used DMV sys.dm_os_sys_info. I just upgraded my SQL Server edition from 2008 R2 to SQL Server 2012 RC0 and it suddenly stopped working. Well, this is not the production server so the issue is not big yet but eventually I need to resolve this error. Any suggestion?” The funny thing was original email was very long but it did not talk about what is the exact error beside the query is not working. I think this is the disadvantage of being too friendly on email sometime. Well, never the less, I quickly looked at the DMV on my SQL Server 2008 R2 and SQL Server 2012 RC0 version. To my surprise I found out that there were few columns which are renamed in SQL Server 2012 RC0. Usually when people see breaking changes they do not like it but when I see these changes I was happy as new names were meaningful and additionally their new conversion is much more practical and useful. Here are the columns previous names - Previous Column Name New Column Name physical_memory_in_bytes physical_memory_kb bpool_commit_target committed_target_kb bpool_visible visible_target_kb virtual_memory_in_bytes virtual_memory_kb bpool_commited committed_kb If you read it carefully you will notice that new columns now display few results in the KB whereas earlier result was in bytes. When I see the results in bytes I always get confused as I could not guess what exactly it will convert to. I like to see results in kb and I am glad that new columns are now displaying the results in the kb. I sent the details of the new columns to my friend and ask him to check the columns used in application. From my comment he quickly realized why he was facing error and fixed it immediately. Overall – all was well at the end and I learned something new. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Public Training and Private Training – Differences and Similarities

    - by pinaldave
    Earlier this year, I was on Road SQL Server Seminars. I did many SQL Server Performance Trainings and SQL Server Performance Consultations throughout the year but I feel the most rewarding exercise is always the one when instructor learns something from students, too. I was just talking to my wife, Nupur – she manages my logistics and administration related activities – and she pointed out that this year I have done 62% consultations and 38% trainings. I was bit surprised as I thought the numbers would be reversed. Every time I review the year, I think of training done at organizations. Well, I cannot argue with reality, I have done more consultations (some would call them projects) than training. I told my wife that I enjoy consultations more than training. She promptly asked me a question which was not directly related but made me think for long time, and in the end resulted in this blog post. Nupur asked me: what do I enjoy the most, public training or private training? I had a long conversation with her on this subject. I am not going to write long blog post which can change your life here. This is rather a small post condensing my one hour discussion into 200 words. Public Training is fun because… There are lots of different kinds of attendees There are always vivid questions Lots of questions on questions Less interest in theory and more interest in demos Good opportunity of future business Private Training is fun because… There is a focused interest One question is discussed deeply because of existing company issues More interest in “how it happened” concepts – under the hood operations Good connection with attendees This is also a good opportunity of future business Here I will stop my monologue and I want to open up this question to all of you: Question to Attendees - Which one do you enjoy the most – Public Training or Private Training? Question to Trainers - What do you enjoy the most – Public Training or Private Training? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQL Training, SQLAuthority News, T SQL, Technology

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  • SQL SERVER – Introduction to PERCENTILE_DISC() – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical function PERCENTILE_DISC(). The book online gives following definition of this function: Computes a specific percentile for sorted values in an entire rowset or within distinct partitions of a rowset in Microsoft SQL Server 2012 Release Candidate 0 (RC 0). For a given percentile value P, PERCENTILE_DISC sorts the values of the expression in the ORDER BY clause and returns the value with the smallest CUME_DIST value (with respect to the same sort specification) that is greater than or equal to P. If you are clear with understanding of the function – no need to read further. If you got lost here is the same in simple words – find value of the column which is equal or more than CUME_DIST. Before you continue reading this blog I strongly suggest you read about CUME_DIST function over here Introduction to CUME_DIST – Analytic Functions Introduced in SQL Server 2012. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, CUME_DIST() OVER(PARTITION BY SalesOrderID ORDER BY ProductID ) AS CDist, PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS PercentileDisc FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: You can see that I have used PERCENTILE_DISC(0.5) in query, which is similar to finding median but not exactly. PERCENTILE_DISC() function takes a percentile as a passing parameters. It returns the value as answer which value is equal or great to the percentile value which is passed into the example. For example in above example we are passing 0.5 into the PERCENTILE_DISC() function. It will go through the resultset and identify which rows has values which are equal to or great than 0.5. In first example it found two rows which are equal to 0.5 and the value of ProductID of that row is the answer of PERCENTILE_DISC(). In some third windowed resultset there is only single row with the CUME_DIST() value as 1 and that is for sure higher than 0.5 making it as a answer. To make sure that we are clear with this example properly. Here is one more example where I am passing 0.6 as a percentile. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, CUME_DIST() OVER(PARTITION BY SalesOrderID ORDER BY ProductID ) AS CDist, PERCENTILE_DISC(0.6) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS PercentileDisc FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: The result of the PERCENTILE_DISC(0.6) is ProductID of which CUME_DIST() is more than 0.6. This means for SalesOrderID 43670 has row with CUME_DIST() 0.75 is the qualified row, resulting answer 773 for ProductID. I hope this explanation makes it further clear. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Three Puzzling Questions – Need Your Answer

    - by pinaldave
    Last week I had asked three questions on my blog. I got very good response to the questions. I am planning to write summary post for each of three questions next week. Before I write summary post and give credit to all the valid answers. I was wondering if I can bring to notice of all of you this week. Why SELECT * throws an error but SELECT COUNT(*) does not This is indeed very interesting question as not quite many realize that this kind of behavior SQL Server demonstrates out of the box. Once you run both the code and read the explanation it totally makes sense why SQL Server is behaving how it is behaving. Also there is connect item is associated with it. Also read the very first comment by Rob Farley it also shares very interesting detail. Statistics are not Updated but are Created Once This puzzle has multiple right answer. I am glad to see many of the correct answer as a comment to this blog post. Statistics are very important and it really helps SQL Server Engine to come up with optimal execution plan. DBA quite often ignore statistics thinking it does not need to be updated, as they are automatically maintained if proper database setting is configured (auto update and auto create). Well, in this question, we have scenario even though auto create and auto update statistics are ON, statistics is not updated. There are multiple solutions but what will be your solution in this case? When to use Function and When to use Stored Procedure This question is rather open ended question – there is no right or wrong answer. Everybody developer has always used functions and stored procedures. Here is the chance to justify when to use Stored Procedure and when to use Functions. I want to acknowledge that they can be used interchangeably but there are few reasons when one should not do that. There are few reasons when one is better than other. Let us discuss this here. Your opinion matters. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Performance, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLAuthority News, SQLServer, T SQL, Technology

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  • SQL SERVER – Sharing your ETL Resources Across Applications with Ease

    - by pinaldave
    Frequently an organization will find that the same resources are used in multiple ETL applications, for example, the same database, general purpose processing logic, or file system locations.  Creating an easy way to reuse these resources across multiple applications would increase efficiency and reduce errors.  Moreover, not every ETL developer has the same skill set, and it is likely that one developer will be more adept at writing code while another is more comfortable configuring database connections.  Real productivity gains will come when these developers are able to work independently while still making their work available to others assigned to the same project.  These are the benefits of a centralized version control system. Of course, most version control systems could be used to store and serve files, but the real need is to store and serve entire ETL applications so that each developer’s ongoing work can immediately benefit from another developer’s completed work.  In other words, the version control system needs to be tightly integrated with the tools used to develop the ETL application. The following screen shot shows such a tool. Desktop ETL tool that tightly integrates with a central version control system Developers can checkout or commit entire projects or just a single artifact.  Each artifact may be managed independently so if you need to go back to an earlier version of one artifact, changes you may have made to other artifacts are not lost.  By being tightly integrated into the graphical environment used to create and edit the project artifacts, it is extremely easy and straight-forward to move your files to and from the version control system and there is no dependency on another vendor’s version control system.  The built in version control system is optimized for managing the artifacts of ETL applications. It is equally important that the version control system supports all of the actions one typically performs such as rollbacks, locking and unlocking of files, and the ability to resolve conflicts.  Note that this particular ETL tool also has the capability to switch back and forth between multiple version control systems. It also needs to be easy to determine the status of an artifact.  Not just that it has been committed or modified, but when and by whom.  Generally you must query the version control system for this information, but having it displayed within the development environment is more desirable. Who’s ETL tool works in this fashion?  Last month I mentioned the data integration solution offered by expressor software.  The version control features I described in this post are all available in their just released expressor 3.1 Standard Edition through the integration of their expressor Studio development environment with a centralized metadata repository and version control system. You can download their Studio application, which is free, or evaluate the full Standard Edition on your own hardware.  It may be worth your time. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical functions FIRST_VALUE() and LAST_VALUE(). This function returns first and last value from the list. It will be very difficult to explain this in words so I’d like to attempt to explain its function through a brief example. Instead of creating a new table, I will be using the AdventureWorks sample database as most developers use that for experiment purposes. Now let’s have fun following query: USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: What’s the most interesting thing here is that as we go from row 1 to row 10, the value of the FIRST_VALUE() remains the same but the value of the LAST_VALUE is increasing. The reason behind this is that as we progress in every line – considering that line and all the other lines before it, the last value will be of the row where we are currently looking at. To fully understand this statement, see the following figure: This may be useful in some cases; but not always. However, when we use the same thing with PARTITION BY, the same query starts showing the result which can be easily used in analytical algorithms and needs. Let us have fun through the following query: Let us fun following query. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: Let us understand how PARTITION BY windows the resultset. I have used PARTITION BY SalesOrderID in my query. This will create small windows of the resultset from the original resultset and will follow the logic or FIRST_VALUE and LAST_VALUE in this resultset. Well, this is just an introduction to these functions. In the future blog posts we will go deeper to discuss the usage of these two functions. By the way, these functions can be applied over VARCHAR fields as well and are not limited to the numeric field only. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Introduction to CUME_DIST – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    This blog post is written in response to the T-SQL Tuesday post of Prox ‘n’ Funx. This is a very interesting subject. By the way Brad Schulz is my favorite guy when it is about blogging. I respect him as well learn a lot from him. Everybody is writing something new his subject, I decided to start SQL Server 2012 analytic functions series. SQL Server 2012 introduces new analytical function CUME_DIST(). This function provides cumulative distribution value. It will be very difficult to explain this in words so I will attempt small example to explain you this function. Instead of creating new table, I will be using AdventureWorks sample database as most of the developer uses that for experiment. Let us fun following query. USE AdventureWorks GO SELECT SalesOrderID, OrderQty, CUME_DIST() OVER(ORDER BY SalesOrderID) AS CDist FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY CDist DESC GO Above query will give us following result. Now let us understand what is the formula behind CUME_DIST and why the values in SalesOrderID = 43670 are 1. Let us take more example and be clear about why the values in SalesOrderID = 43667 are 0.5. Now let us enhence the same example and use PARTITION BY into the OVER clause and see the results. Run following query in SQL Server 2012. USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, CUME_DIST() OVER(PARTITION BY SalesOrderID ORDER BY ProductID ) AS CDist FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID DESC, CDist DESC GO Now let us see the result of this query. We are have changed the ORDER BY clause as well partitioning by SalesOrderID. You can see that CUME_DIST() function provides us different results. Additionally now we see value 1 multiple times. As we are using partitioning for each group of SalesOrderID we get the CUME_DIST() value. CUME_DIST() was long awaited Analytical function and I am glad to see it in SQL Server 2012. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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