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• SQLAuthority News – Milestone of 1300th Post and A Few Updates

  - by pinaldave

  Today is my 1300th blog post and I realize that my blog has been quite running such a long journey. I have been writing for a lengthy time on this tech blog. Today I would like to go back and briefly recall the posts that were part of my blog’s history. Read all list of all my blog posts here. This blog only started as a list of personal bookmarks. I used to just write down scripts on the blog for my personal use. I was the one who wrote many scripts here for the servers that I was maintaining to keep them polished. I have included many links in my first blog posts which I view as just a collection of bookmarks on my very own blog; no intentions of publishing other contents besides the scripts, at all. Gradually, I realized that people read my blog and follow the advices which were supposedly meant only for me. I tried to write a code and a script which are generic in nature, so anyone can just use it right away. Nothing is perfect. When I was writing the last 1299 posts (and having 14 Million+ views), I have made a few mistakes and tweaks that I thoughtfully accepted. These are corrections that were pointed out by many kind souls and readers like you, which have helped me develop wonderful blogging experiences. I am very glad that I have this blog wherein I can express myself. After all, I would have not reached where I am today if I have kept myself worried in terms of expressing my knowledge and understanding SQL Server. I am happy that many of you appreciated my efforts and supported me all the way, which also helped me achieve where I am now. I promise to learn more about this fascinating subject and, of course, continue to share whatever I will learn to my dear readers. Again, I really thank YOU for reading this blog and supporting the SQL community. Reference: Pinal Dave (http://blog.SQLAuthority.com), Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology Tagged: SQL Milestone

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• SQLAuthority News – Monthly Roundup of Best SQL Posts

  - by pinaldave

  After receiving lots of requests from different readers for long time I have decided to write first monthly round up. If all of you like it I will continue writing the same every month. In fact, I really like the idea as I was able to go back and read all of my posts written in this month. This month was started with answering one of the most common question asked me to about What is Adventureworks? Many of you know the answer but to the surprise more number of the reader did not know the answer. There were few extra blog post which were in the same line as following. SQL SERVER – The Difference between Dual Core vs. Core 2 Duo SQLAuthority News – Wireless Router Security and Attached Devices – Complex Password SQL SERVER – DATE and TIME in SQL Server 2008 DMVs are also one of the most handy tools available in SQL Server, I have written following blog post where I have used DMV in scripts. SQL SERVER – Get Latest SQL Query for Sessions – DMV SQL SERVER – Find Most Expensive Queries Using DMV SQL SERVER – List All the DMV and DMF on Server I was able to write two follow-up of my earlier series where I was finding the size of the indexes using different SQL Scripts. And in fact one of the article Powershell is used as well. This was my very first attempt to use Powershell. SQL SERVER – Size of Index Table for Each Index – Solution 2 SQL SERVER – Size of Index Table for Each Index – Solution 3 – Powershell SQL SERVER – Four Posts on Removing the Bookmark Lookup – Key Lookup Without realizing I wrote series of the blog post on disabled index here is its complete list. I plan to write one more follow-up list on the same. SQL SERVER – Disable Clustered Index and Data Insert SQL SERVER – Understanding ALTER INDEX ALL REBUILD with Disabled Clustered Index SQL SERVER – Disabled Index and Update Statistics Two special post which I found very interesting to write are as following. SQL SERVER – SHRINKFILE and TRUNCATE Log File in SQL Server 2008 SQL SERVER – Simple Example of Snapshot Isolation – Reduce the Blocking Transactions In personal adventures, I won the Community Impact Award for Last Year from Microsoft. Please leave your comment about how can I improve this round up or what more details I should include in the same. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology

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• SQL SERVER – WRITELOG – Wait Type – Day 17 of 28

  - by pinaldave

  WRITELOG is one of the most interesting wait types. So far we have seen a lot of different wait types, but this log type is associated with log file which makes it interesting to deal with. From Book On-Line: WRITELOG Occurs while waiting for a log flush to complete. Common operations that cause log flushes are checkpoints and transaction commits. WRITELOG Explanation: This wait type is usually seen in the heavy transactional database. When data is modified, it is written both on the log cache and buffer cache. This wait type occurs when data in the log cache is flushing to the disk. During this time, the session has to wait due to WRITELOG. I have recently seen this wait type’s persistence at my client’s place, where one of the long-running transactions was stopped by the user causing it to roll back. In the future, I will see if I could re-create this situation once again on my machine to validate the relation. Reducing WRITELOG wait: There are several suggestions to reduce this wait stats: Move Transaction Log to Separate Disk from mdf and other files. Avoid cursor-like coding methodology and frequent committing of statements. Find the most active file based on IO stall time based on 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. There are two excellent resources by Paul Randal, I suggest you understand the subject from those videos. The links to videos are here and here. 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 – Best Reference – Wait Type – Day 27 of 28

  - by pinaldave

  I have great learning experience to write my article series on Extended Event. This was truly learning experience where I have learned way more than I would have learned otherwise. Besides my blog series there was excellent quality reference available on internet which one can use to learn this subject further. Here is the list of resources (in no particular order): sys.dm_os_wait_stats (Book OnLine) – This is excellent beginning point and official documentations on the wait types description. SQL Server Best Practices Article by Tom Davidson – I think this document goes without saying the BEST reference available on this subject. Performance Tuning with Wait Statistics by Joe Sack – One of the best slide deck available on this subject. It covers many real world scenarios. Wait statistics, or please tell me where it hurts by Paul Randal – Notes from real world from SQL Server Skilled Master Paul Randal. The SQL Server Wait Type Repository… by Bob Ward – A thorough article on wait types and its resolution. A MUST read. Tracking Session and Statement Level Waits by by Jonathan Kehayias – A unique article on the subject where wait stats and extended events are together. Wait Stats Introductory References By Jimmy May – Excellent collection of the reference links. Great Resource On SQL Server Wait Types by Glenn Berry – A perfect DMV to find top wait stats. Performance Blog by Idera – In depth article on top of the wait statistics in community. I have listed all the reference I have found in no particular order. If I have missed any good reference, please leave a comment and I will add the reference in the list. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Tracking Session and Statement Level Waits 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 – FT_IFTS_SCHEDULER_IDLE_WAIT – Full Text – Wait Type – Day 13 of 28

  - by pinaldave

  In the last few days during this series, I got many question about this Wait type. It would be great if you read my original related wait stats query in the first post because I have filtered it out in WHERE clause. However, I still get questions about this being one of the most wait types they encounter. The truth is, this is a background task processing and it really does not matter and it should be filtered out. There are many new Wait types related to Full Text Search that are introduced in SQL Server 2008. If you run the following query, you will be able to find them in the list. Currently there is not enough information for all of them available on BOL or any other place. But don’t worry; I will write an in-depth article when I learn more about them. SELECT * FROM sys.dm_os_wait_stats WHERE wait_type LIKE 'FT_%' The result set will contain following rows. FT_RESTART_CRAWL FT_METADATA_MUTEX FT_IFTSHC_MUTEX FT_IFTSISM_MUTEX FT_IFTS_RWLOCK FT_COMPROWSET_RWLOCK FT_MASTER_MERGE FT_IFTS_SCHEDULER_IDLE_WAIT We have understood so far that there is not much information available. But the problem is when you have this Wait type, what should you do?  The answer is to filter them out for the moment (i.e, do not pay attention on them) and focus on other pressing issues in wait stats or performance tuning. Here are two of my informal suggestions, which are totally independent from wait stats: Turn off the Full Text Search service in your system if you are  not necessarily using it on your server. Learn proper Full Text Search methodology. You can get Michael Coles’ book: Pro Full-Text Search in SQL Server 2008. Now I invite you to speak out your suggestions or any input regarding Full Text-related best practices and wait stats issue. Please leave a comment. 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 discussions of Wait Stats in this blog are generic and vary 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 – Introduction to Adaptive ETL Tool – How adaptive is your ETL?

  - by pinaldave

  I am often reminded by the fact that BI/data warehousing infrastructure is very brittle and not very adaptive to change. There are lots of basic use cases where data needs to be frequently loaded into SQL Server or another database. What I have found is that as long as the sources and targets stay the same, SSIS or any other ETL tool for that matter does a pretty good job handling these types of scenarios. But what happens when you are faced with more challenging scenarios, where the data formats and possibly the data types of the source data are changing from customer to customer?  Let’s examine a real life situation where a health management company receives claims data from their customers in various source formats. Even though this company supplied all their customers with the same claims forms, they ended up building one-off ETL applications to process the claims for each customer. Why, you ask? Well, it turned out that the claims data from various regional hospitals they needed to process had slightly different data formats, e.g. “integer” versus “string” data field definitions.  Moreover the data itself was represented with slight nuances, e.g. “0001124” or “1124” or “0000001124” to represent a particular account number, which forced them, as I eluded above, to build new ETL processes for each customer in order to overcome the inconsistencies in the various claims forms.  As a result, they experienced a lot of redundancy in these ETL processes and recognized quickly that their system would become more difficult to maintain over time. So imagine for a moment that you could use an ETL tool that helps you abstract the data formats so that your ETL transformation process becomes more reusable. Imagine that one claims form represents a data item as a string – acc_no(varchar) – while a second claims form represents the same data item as an integer – account_no(integer). This would break your traditional ETL process as the data mappings are hard-wired.  But in a world of abstracted definitions, all you need to do is create parallel data mappings to a common data representation used within your ETL application; that is, map both external data fields to a common attribute whose name and type remain unchanged within the application. acc_no(varchar) is mapped to account_number(integer) expressor Studio first claim form schema mapping account_no(integer) is also mapped to account_number(integer) expressor Studio second claim form schema mapping All the data processing logic that follows manipulates the data as an integer value named account_number. Well, these are the kind of problems that that the expressor data integration solution automates for you.  I’ve been following them since last year and encourage you to check them out by downloading their free expressor Studio ETL software. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Business Intelligence, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: ETL, SSIS

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• SQL SERVER – 4 Tips for ETL Software IDE Developers

  - by pinaldave

  In a previous blog, I introduced the notion of Semantic Types. To an end-user, a seamlessly integrated semantic typing engine significantly increases the ease of use of an ETL IDE (integrated development environment, or developer studio). This led me to think about other ease-of-use issues I have encountered while building ETL applications. When I get stumped while programming, I find myself asking the variations on these questions: “How do I…?” “Now what?” “Why isn’t this working?” “Why do I have to redo the work I just did?” It seems to me that a good ETL IDE will anticipate these questions and seek to answer them before they are even asked. So here are my tips to help software vendors build developer IDEs that actually make development easier. How do I…? While developing an ETL application, have you ever asked yourself: “How do I set up the connection to my SQL Server database?”,“How do I import my table definitions from Access?”, etc. An easy answer might be “read the manual” but sometimes product manuals are not robust or easily accessible. So, integrating robust how-to instructions directly into your ETLstudio would help users get the information they need at the time they need it. Now what? IDEs in general know where you last clicked or performed an action using an input device such as a keyboard; so they should be able to reasonably predict the design context you are in and suggest the next steps accordingly. Context-sensitive suggestions based on the state of the user’s work will help users move forward in ETL application development. Why isn’t this working? Or why do I have to wait till I compile to be told about a critical design issue? If an ETL IDE is smart enough to signal to users what in their design structures is left to be completed or has been completed incorrectly, then the developer can spend much less time in the designàcompileàerror-correct loop. Just-in-time validation helps users detect and correct programming errors earlier in the ETL development life cycle. Why do I have to redo the work I just did? In ETL development, schemas, transformation rules, connectivity objects, etc., can be reused in various situations. Using mouse-clicks to build and manage libraries of reusable design objects implies that the application development effort should decrease over time and as the library acquires more objects. I met a great company at SQL Pass that is trying to address many of these usability issues. Check them out at www.expressor-software.com. What other ease-of-use suggestions do you have for ETL software vendors? Please post your valuable comments. ?Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Best Practices, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: ETL

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• SQL SERVER – What the Business Says Is Not What the Business Wants

  - by pinaldave

  This blog post is written in response to T-SQL Tuesday hosted by Steve Jones. Steve raised a very interesting question; every DBA and Database Developer has already faced this situation. When I read the topic, I felt that I can write several different examples here. Today, I will cover this scenario, which seems quite amusing. Shrinking Database Earlier this year, I was working on SQL Server Performance Tuning consultancy; I had faced very interesting situation. No matter how much I attempt to reduce the fragmentation, I always end up with heavy fragmentation on the server. After careful research, I figured out that one of the jobs was continuously Shrinking the Database – which is a very bad practice. I have blogged about my experience over here SQL SERVER – SHRINKDATABASE For Every Database in the SQL Server. I removed the incorrect shrinking process right away; once it was removed, everything continued working as it should be. After a couple of days, I learned that one of their DBAs had put back the same DBCC process. I requested the Senior DBA to find out what is going on and he came up with the following reason: “Business Requirement.” I cannot believe this! Now, it was time for me to go deep into the subject. Moreover, it had become necessary to understand the need. After talking to the concerned people here, I understood what they needed. Please read the exact business need in their own language. The Shrinking “Business Need” “We shrink the database because if we take backup after shrinking the database, the size of the same is smaller. Once we take backup, we have to send it to our remote location site. Our business requirement is that we need to always make sure that the file is smallest when we transfer it to remote server.” The backup is not affected in any way if you shrink the database or not. The size of backup will be the same. After a couple of the tests, they agreed with me. Shrinking will create performance issues for the same as it will introduce heavy fragmentation in the database. The Real Solution The real business need was that they needed the smallest possible backup file. We finally implemented a quick solution which they are still using to date. The solution was compressed backup. I have written about this subject in detail few years before SQL SERVER – 2008 – Introduction to New Feature of Backup Compression. Compressed backup not only creates a small filesize but also increases the speed of the database as well. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Best Practices, Pinal Dave, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• SQL SERVER – Index Created on View not Used Often – Observation of the View – Part 2

  - by pinaldave

  Earlier, I have written an article about SQL SERVER – Index Created on View not Used Often – Observation of the View. I received an email from one of the readers, asking if there would no problems when we create the Index on the base table. Well, we need to discuss this situation in two different cases. Before proceeding to the discussion, I strongly suggest you read my earlier articles. To avoid the duplication, I am not going to repeat the code and explanation over here. In all the earlier cases, I have explained in detail how Index created on the View is not utilized. SQL SERVER – Index Created on View not Used Often – Limitation of the View 12 SQL SERVER – Index Created on View not Used Often – Observation of the View SQL SERVER – Indexed View always Use Index on Table As per earlier blog posts, so far we have done the following: Create a Table Create a View Create Index On View Write SELECT with ORDER BY on View However, the blog reader who emailed me suggests the extension of the said logic, which is as follows: Create a Table Create a View Create Index On View Write SELECT with ORDER BY on View Create Index on the Base Table Write SELECT with ORDER BY on View After doing the last two steps, the question is “Will the query on the View utilize the Index on the View, or will it still use the Index of the base table?“ Let us first run the Create example. 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 -- Create Index on Original Table -- On Column ID1 CREATE UNIQUE CLUSTERED INDEX [IX_OriginalTable] ON mySampleTable ( ID1 ASC ) GO -- On Column ID2 CREATE UNIQUE NONCLUSTERED INDEX [IX_OriginalTable_ID2] ON mySampleTable ( ID2 ) GO -- Select from view SELECT ID1,ID2,SomeData FROM SampleView ORDER BY ID2 GO Now let us see the execution plans for both of the SELECT statement. Before Index on Base Table (with Index on View): After Index on Base Table (with Index on View): Looking at both executions, it is very clear that with or without, the View is using Indexes. Alright, I have written 11 disadvantages of the Views. Now I have written one case where the View is using Indexes. Anybody who says that I am being harsh on Views can say now that I found one place where Index on View can be helpful. 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, SQLServer, T SQL, Technology

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• SQL SERVER – Automated Type Conversion using Expressor Studio

  - by pinaldave

  Recently I had an interesting situation during my consultation project. Let me share to you how I solved the problem using Expressor Studio. Consider a situation in which you need to read a field, such as customer_identifier, from a text file and pass that field into a database table. In the source file’s metadata structure, customer_identifier is described as a string; however, in the target database table, customer_identifier is described as an integer. Legitimately, all the source values for customer_identifier are valid numbers, such as “109380”. To implement this in an ETL application, you probably would have hard-coded a type conversion function call, such as: output.customer_identifier=stringToInteger(input.customer_identifier) That wasn’t so bad, was it? For this instance, programming this hard-coded type conversion function call was relatively easy. However, hard-coding, whether type conversion code or other business rule code, almost always means that the application containing hard-coded fields, function calls, and values is: a) specific to an instance of use; b) is difficult to adapt to new situations; and c) doesn’t contain many reusable sub-parts. Therefore, in the long run, applications with hard-coded type conversion function calls don’t scale well. In addition, they increase the overall level of effort and degree of difficulty to write and maintain the ETL applications. To get around the trappings of hard-coding type conversion function calls, developers need an access to smarter typing systems. Expressor Studio product offers this feature exactly, by providing developers with a type conversion automation engine based on type abstraction. The theory behind the engine is quite simple. A user specifies abstract data fields in the engine, and then writes applications against the abstractions (whereas in most ETL software, developers develop applications against the physical model). When a Studio-built application is run, Studio’s engine automatically converts the source type to the abstracted data field’s type and converts the abstracted data field’s type to the target type. The engine can do this because it has a couple of built-in rules for type conversions. So, using the example above, a developer could specify customer_identifier as an abstract data field with a type of integer when using Expressor Studio. Upon reading the string value from the text file, Studio’s type conversion engine automatically converts the source field from the type specified in the source’s metadata structure to the abstract field’s type. At the time of writing the data value to the target database, the engine doesn’t have any work to do because the abstract data type and the target data type are just the same. Had they been different, the engine would have automatically provided the conversion. ?Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Database, Pinal Dave, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology Tagged: SSIS

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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_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 – 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 – 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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