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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 – 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 – Retrieve and Explore Database Backup without Restoring Database – Idera virtual databas

  - by pinaldave

  I recently downloaded Idera’s SQL virtual database, and tested it. There are a few things about this tool which caught my attention. My Scenario It is quite common in real life that sometimes observing or retrieving older data is necessary; however, it had changed as time passed by. The full database backup was 40 GB in size, and, to restore it on our production server, it usually takes around 16 to 22 minutes, depending on the load server that is usually present. This range in time varies from one server to another as per the configuration of the computer. Some other issues we used to have are the following: When we try to restore a large 40-GB database, we needed at least that much space on our production server. Once in a while, we even had to make changes in the restored database, and use the said changed and restored database for our purpose, making it more time-consuming. My Solution I have heard a lot about the Idera’s SQL virtual database tool.. Well, right after we started to test this tool, we found out that it really delivers what it promises. Using this software was very easy and we were able to restore our database from backup in less than 2 minutes, sparing us from the usual longer time of 16–22 minutes. The needful was finished in a total of 10 minutes. Another interesting observation is that there is no need to have an additional space for restoring the database. For complete database restoration, the single additional MB on the drive is not required anymore. We can use the database in the same way as our regular database, and there is no need for any additional configuration and setup. Let us look at the most relevant points of this product based on my initial experience: Quick restoration of the database backup No additional space required for database restoration virtual database has no physical .MDF or .LDF The database which is restored is, in fact, the backup file converted in the virtual database. DDL and DML queries can be executed against this virtually restored database. Regular backup operation can be implemented against virtual database, creating a physical .bak file that can be used for future use. There was no observed degradation in performance on the original database as well the restored virtual database. Additional T-SQL queries can be let off on the virtual database. Well, this summarizes my quick review. And, as I was saying, I am very impressed with the product and I plan to explore it more. There are many features that I have noticed in this tool, which I think can be very useful if properly understood. I had taken a few screenshots using my demo database afterwards. Let us see what other things this tool can do besides the mentioned activities. I am surprised with its performance so I want to know how exactly this feature works, specifically in the matter of why it does not create any additional files and yet, it still allows update on the virtually restored database. I guess I will have to send an e-mail to the developers of Idera and try to figure this out from them. I think this tool is very useful, and it delivers a high level of performance way more than what I expected. Soon, I will write a review for additional uses of SQL virtual database.. If you are using SQL virtual database in your production environment, I am eager to learn more about it and your experience while using it. The ‘Virtual’ Part of virtual database When I set out to test this software, I thought virtual database had something to do with Hyper-V or visualization. In fact, the virtual database is a kind of database which shows up in your SQL Server Management Studio without actually restoring or even creating it. This tool creates a database in SSMS from the backup of the same database. The backup, however, works virtually the same way as original database. Potential Usage of virtual database: As soon as I described this tool to my teammate, I think his very first reaction was, “hey, if we have this then there is no need for log shipping.” I find his comment very interesting as log shipping is something where logs are moved to another server. In fact, there are no updates on the database from log; I would rather compare it with Snapshot Replication. In fact, whatever we use, snapshot replicated database can be similarly used and configured with virtual database. I totally believe that we can use it for reporting purpose. In fact, after this database was configured, I think the uses of this tool are unlimited. I will have to spend some more time studying it and will get back to you. Click on images to see larger images. virtual database Console Harddrive Space before virtual database Setup Attach Full Backup Screen Backup on Harddrive Attach Full Backup Screen with Settings virtual database Setup – less than 60 sec virtual database Setup – Online Harddrive Space after virtual database Setup Point in Time Recovery Option – Timeline View virtual database Summary No Performance Difference between Regular DB vs Virtual DB Please note that all SQL Server MVP gets free license of this software. Reference: Pinal Dave (http://blog.SQLAuthority.com), Idera (virtual database) Filed under: Database, Pinal Dave, SQL, SQL Add-On, SQL Authority, SQL Backup and Restore, SQL Data Storage, SQL Query, SQL Server, SQL Tips and Tricks, SQL Utility, SQLAuthority News, T SQL, Technology Tagged: Idera

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• SQL SERVER – Beginning SQL Server: One Step at a Time – SQL Server Magazine

  - by pinaldave

  I am glad to announce that along with SQLAuthority.com, I will be blogging on the prominent site of SQL Server Magazine. My very first blog post there is already live; read here: Beginning SQL Server: One Step at a Time. My association with SQL Server Magazine has been quite long, I have written nearly 7 to 8 SQL Server articles for the print magazine and it has been a great experience. I used to stay in the United States at that time. I moved back to India for good, and during this process, I had put everything on hold for a while. Just like many things, “temporary” things become “permanent” – coming back to SQLMag was on hold for long time. Well, this New Year, things have changed – once again, I am back with my online presence at SQLMag.com. Everybody is a beginner at every task or activity at some point of his/her life: spelling words for the first time; learning how to drive for the first time, etc. No one is perfect at the start of any task, but every human is different. As time passes, we all develop our interests and begin to study our subject of interest. Most of us dream to get a job in the area of our study – however things change as time passes. I recently read somewhere online (I could not find the link again while writing this one) that all the successful people in various areas have never studied in the area in which they are successful. After going through a formal learning process of what we love, we refuse to stop learning, and we finally stop changing career and focus areas. We move, we dare and we progress. IT field is similar to our life. New IT professionals come to this field every day. There are two types of beginners – a) those who are associated with IT field but not familiar with other technologies, and b) those who are absolutely new to the IT field. Learning a new technology is always exciting and overwhelming for enthusiasts. I am working with database (in particular) for SQL Server for more than 7 years but I am still overwhelmed with so many things to learn. I continue to learn and I do not think that I should ever stop doing so. Just like everybody, I want to be in the race and get ahead in learning the technology. For the same, I am always looking for good guidance. I always try to find a good article, blog or book chapter, which can teach me what I really want to learn at this stage in my career and can be immensely helpful. Quite often, I prefer to read the material where the author does not judge me or assume my understanding. I like to read new concepts like a child, who takes his/her first steps of learning without any prior knowledge. Keeping my personal philosophy and preference in mind, I will be blogging on SQL Server Magazine site. I will be blogging on the beginners stuff. I will be blogging for them, who really want to start and make a mark in this area. I will be blogging for all those who have an extreme passion for learning. I am happy that this is a good start for this year. One of my resolutions is to help every beginner. It is totally possible that in future they all will grow and find the same article quite ‘easy‘ – well when that happens, it indicates the success of the article and material! Well, I encourage everybody to read my SQL Server Magazine blog – I will be blogging there frequently on various topics. To begin, we will be talking about performance tuning, and I assure that I will not shy away from other multiple areas. Read my SQL Server Magazine Blog: Beginning SQL Server: One Step at a Time I think the title says it all. Do leave your comments and feedback to indicate your preference of subject and interest. I am going to continue writing on subject, and the aim is of course to help grow in this field. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology

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• SQL SERVER – World Shapefile Download and Upload to Database – Spatial Database

  - by pinaldave

  During my recent, training I was asked by a student if I know a place where he can download spatial files for all the countries around the world, as well as if there is a way to upload shape files to a database. Here is a quick tutorial for it. VDS Technologies has all the spatial files for every location for free. You can download the spatial file from here. If you cannot find the spatial file you are looking for, please leave a comment here, and I will send you the necessary details. Unzip the file to a folder and it will have the following content. Then, download Shape2SQL tool from SharpGIS. This is one of the best tools available to convert shapefiles to SQL tables. Afterwards, run the .exe file. When the file is run for the first time, it will ask for the database properties. Provide your database details. Select the appropriate shape files and the tool will fill up the essential details automatically. If you do not want to create the index on the column, uncheck the box beside it. The screenshot below is simply explains the procedure. You also have to be careful regarding your data, whether that is GEOMETRY or GEOGRAPHY. In this example,  it is GEOMETRY data. Click “Upload to Database”. It will show you the uploading process. Once the shape file is uploaded, close the application and open SQL Server Management Studio (SSMS). Run the following code in SSMS Query Editor. USE Spatial GO SELECT * FROM dbo.world GO This will show the complete map of world after you click on Spatial Results in Spatial Tab. In Spatial Results Set, the Zoom feature is available. From the Select label column, choose the country name in order to show the country name overlaying the country borders. Let me know if this tutorial is helpful enough. I am planning to write a few more posts about this later. Note: Please note that the images displayed here do not reflect the original political boundaries. These data are pretty old and can probably draw incorrect maps as well. I have personally spotted several parts of the map where some countries are located a little bit inaccurately. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Add-On, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Spatial, SQL Tips and Tricks, SQL Utility, T SQL, Technology

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• SQL SERVER – Maximize Database Performance with DB Optimizer – SQL in Sixty Seconds #054

  - by Pinal Dave

  Performance tuning is an interesting concept and everybody evaluates it differently. Every developer and DBA have different opinion about how one can do performance tuning. I personally believe performance tuning is a three step process Understanding the Query Identifying the Bottleneck Implementing the Fix While, we are working with large database application and it suddenly starts to slow down. We are all under stress about how we can get back the database back to normal speed. Most of the time we do not have enough time to do deep analysis of what is going wrong as well what will fix the problem. Our primary goal at that time is to just fix the database problem as fast as we can. However, here is one very important thing which we need to keep in our mind is that when we do quick fix, it should not create any further issue with other parts of the system. When time is essence and we want to do deep analysis of our system to give us the best solution we often tend to make mistakes. Sometimes we make mistakes as we do not have proper time to analysis the entire system. Here is what I do when I face such a situation – I take the help of DB Optimizer. It is a fantastic tool and does superlative performance tuning of the system. Everytime when I talk about performance tuning tool, the initial reaction of the people is that they do not want to try this as they believe it requires lots of the learning of the tool before they use it. It is absolutely not true with the case of the DB optimizer. It is a very easy to use and self intuitive tool. Once can get going with the product, in no time. Here is a quick video I have build where I demonstrate how we can identify what index is missing for query and how we can quickly create the index. Entire three steps of the query tuning are completed in less than 60 seconds. If you are into performance tuning and query optimization you should download DB Optimizer and give it a go. Let us see the same concept in following SQL in Sixty Seconds Video: You can Download DB Optimizer and reproduce the same Sixty Seconds experience. Related Tips in SQL in Sixty Seconds: Performance Tuning – Part 1 of 2 – Getting Started and Configuration Performance Tuning – Part 2 of 2 – Analysis, Detection, Tuning and Optimizing 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 Interview Questions and Answers, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Identity

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• SQL SERVER – 2008 – Unused Index Script – Download

  - by pinaldave

  Download Missing Index Script with Unused Index Script Performance Tuning is quite interesting and Index plays a vital role in it. A proper index can improve the performance and a bad index can hamper the performance. Here is the script from my script bank which I use to identify unused indexes on any database. Please note, if you should not drop all the unused indexes this script suggest. This is just for guidance. You should not create more than 5-10 indexes per table. Additionally, this script sometime does not give accurate information so use your common sense. Any way, the scripts is good starting point. You should pay attention to User Scan, User Lookup and User Update when you are going to drop index. The generic understanding is if this values are all high and User Seek is low, the index needs tuning. The index drop script is also provided in the last column. Download Missing Index Script with Unused Index Script -- Unused Index Script -- Original Author: Pinal Dave (C) 2011 SELECT TOP 25 o.name AS ObjectName , i.name AS IndexName , i.index_id AS IndexID , dm_ius.user_seeks AS UserSeek , dm_ius.user_scans AS UserScans , dm_ius.user_lookups AS UserLookups , dm_ius.user_updates AS UserUpdates , p.TableRows , 'DROP INDEX ' + QUOTENAME(i.name) + ' ON ' + QUOTENAME(s.name) + '.' + QUOTENAME(OBJECT_NAME(dm_ius.OBJECT_ID)) AS 'drop statement' FROM sys.dm_db_index_usage_stats dm_ius INNER JOIN sys.indexes i ON i.index_id = dm_ius.index_id AND dm_ius.OBJECT_ID = i.OBJECT_ID INNER JOIN sys.objects o ON dm_ius.OBJECT_ID = o.OBJECT_ID INNER JOIN sys.schemas s ON o.schema_id = s.schema_id INNER JOIN (SELECT SUM(p.rows) TableRows, p.index_id, p.OBJECT_ID FROM sys.partitions p GROUP BY p.index_id, p.OBJECT_ID) p ON p.index_id = dm_ius.index_id AND dm_ius.OBJECT_ID = p.OBJECT_ID WHERE OBJECTPROPERTY(dm_ius.OBJECT_ID,'IsUserTable') = 1 AND dm_ius.database_id = DB_ID() AND i.type_desc = 'nonclustered' AND i.is_primary_key = 0 AND i.is_unique_constraint = 0 ORDER BY (dm_ius.user_seeks + dm_ius.user_scans + dm_ius.user_lookups) ASC GO Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Download, SQL Index, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQLAuthority News – Microsoft SQL Server 2005 Service Pack 4 RTM

  - by pinaldave

  Service Pack 4 (SP4) for Microsoft SQL Server 2005 is now available for download. SQL Server 2005 service packs are cumulative, and this service pack upgrades all service levels of SQL Server 2005 to SP4 . Download Microsoft SQL Server 2005 Service Pack 4 RTM Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Service Pack, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology

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• SQL SERVER – SQL Server Misconceptions and Resolution – A Practical Perspective – TechEd 2012 India

  - by pinaldave

  TechEd India 2012 is just around the corner and I will be presenting there in two different sessions. On the very first day of this event, my presentation will be all about SQL Server Misconceptions and Resolution – A Practical Perspective. The dictionary tells us that a “misconception” means a view or opinion that is incorrect and is based on faulty thinking or understanding. In SQL Server, there are so many misconceptions. In fact, when I hear some of these misconceptions, I feel like fainting at that very moment! Seriously, at one time, I came across the scenario where instead of using INSERT INTO…SELECT, the developer used CURSOR believing that cursor is faster (duh!). Here is the link the blog post related to this. Pinal and Vinod in 2009 I have been presenting in TechEd India for last three years. This is my fourth opportunity to present a technical session on SQL Server. Just like the previous years, I decided to present something different. Here is a novelty of this year: I will be presenting this session with Vinod Kumar. Vinod Kumar and I have a great synergy when we work together. So far, we have written one SQL Server Interview Questions and Answers book and 2 video courses: (1) SQL Server Questions and Answers (2) SQL Server Performance: Indexing Basics. Pinal and Vinod in 2011 When we sat together and started building an outline for this course, we had many options in mind for this tango session. However, we have decided that we will make this session as lively as possible while keeping it natural at the same time. We know our flow and we know our conversation highlight, but we do not know what exactly each of us is going to present. We have decided to challenge each other on stage and push each other’s knowledge to the verge. We promise that the session will be entertaining with lots of SQL Server trivia, tips and tricks. Here are the challenges that I’ll take on: I will puzzle Vinod with my difficult questions I will present such misconception that Vinod will have no resolution for it. I need your help.  Will you help me stump Vinod? If yes, come and attend our session and join me to prove that together we are superior (a friendly brain clash, but we must win!). SQL Server enthusiasts and SQL Server fans are going to have gala time at #TechEdIn as we have a very solid lineup of the speaker and extremely interesting sessions at TechEdIn. Read the complete blog post of Vinod. Session Details Title: SQL Server Misconceptions and Resolution – A Practical Perspective (Add to Calendar) Abstract: “Earth is flat”! – An ancient common misconception, which has been proven incorrect as we progressed in modern times. In this session we will see various database misconceptions prevailing and their resolution with the aid of the demos. In this unique session audience will be part of the conversation and resolution. Date and Time: March 21, 2012, 15:15 to 16:15 Location: Hotel Lalit Ashok - Kumara Krupa High Grounds, Bengaluru – 560001, Karnataka, India. Add to Calendar Please submit your questions in the comments area and I will be for sure discussing them during my session. If I pick your question to discuss during my session, here is your gift I commit right now – SQL Server Interview Questions and Answers Book. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: TechEd, TechEdIn

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• SQL SERVER – SQL Server 2008 with Service Pack 2

  - by pinaldave

  SQL Server 2008 Service Pack 2 has been already released earlier. I suggest that all of you who are running SQL Server 2008 I suggest you updated to SQL Server 2008 Service Pack 2. Download SQL Server 2008 – Service Pack 2 from here. Please note, this is not SQL Server 2008 R2 but it is SQL Server 2008 – Service Pack 2. Test Lab Guide of sQL Server 2008 with Service Pack 2 is also released by Microsoft. This document contains an introduction to SQL Server 2008 with Service Pack 2 and step-by-step instructions for extending the Base Configuration test lab to include a SQL Server 2008 with Service Pack 2 server. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology

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• SQL SERVER – Server Side Paging in SQL Server 2011 Performance Comparison

  - by pinaldave

  Earlier, I have written about SQL SERVER – Server Side Paging in SQL Server 2011 – A Better Alternative. I got many emails asking for performance analysis of paging. Here is the quick analysis of it. The real challenge of paging is all the unnecessary IO reads from the database. Network traffic was one of the reasons why paging has become a very expensive operation. I have seen many legacy applications where a complete resultset is brought back to the application and paging has been done. As what you have read earlier, SQL Server 2011 offers a better alternative to an age-old solution. This article has been divided into two parts: Test 1: Performance Comparison of the Two Different Pages on SQL Server 2011 Method In this test, we will analyze the performance of the two different pages where one is at the beginning of the table and the other one is at its end. Test 2: Performance Comparison of the Two Different Pages Using CTE (Earlier Solution from SQL Server 2005/2008) and the New Method of SQL Server 2011 We will explore this in the next article. This article will tackle test 1 first. Test 1: Retrieving Page from two different locations of the table. Run the following T-SQL Script and compare the performance. SET STATISTICS IO ON; USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 5 SELECT * FROM Sales.SalesOrderDetail ORDER BY SalesOrderDetailID OFFSET @PageNumber*@RowsPerPage ROWS FETCH NEXT 10 ROWS ONLY GO USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 12100 SELECT * FROM Sales.SalesOrderDetail ORDER BY SalesOrderDetailID OFFSET @PageNumber*@RowsPerPage ROWS FETCH NEXT 10 ROWS ONLY GO You will notice that when we are reading the page from the beginning of the table, the database pages read are much lower than when the page is read from the end of the table. This is very interesting as when the the OFFSET changes, PAGE IO is increased or decreased. In the normal case of the search engine, people usually read it from the first few pages, which means that IO will be increased as we go further in the higher parts of navigation. I am really impressed because using the new method of SQL Server 2011,  PAGE IO will be much lower when the first few pages are searched in the navigation. Test 2: Retrieving Page from two different locations of the table and comparing to earlier versions. In this test, we will compare the queries of the Test 1 with the earlier solution via Common Table Expression (CTE) which we utilized in SQL Server 2005 and SQL Server 2008. Test 2 A : Page early in the table -- Test with pages early in table USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 5 ;WITH CTE_SalesOrderDetail AS ( SELECT *, ROW_NUMBER() OVER( ORDER BY SalesOrderDetailID) AS RowNumber FROM Sales.SalesOrderDetail PC) SELECT * FROM CTE_SalesOrderDetail WHERE RowNumber >= @PageNumber*@RowsPerPage+1 AND RowNumber <= (@PageNumber+1)*@RowsPerPage ORDER BY SalesOrderDetailID GO SET STATISTICS IO ON; USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 5 SELECT * FROM Sales.SalesOrderDetail ORDER BY SalesOrderDetailID OFFSET @PageNumber*@RowsPerPage ROWS FETCH NEXT 10 ROWS ONLY GO Test 2 B : Page later in the table -- Test with pages later in table USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 12100 ;WITH CTE_SalesOrderDetail AS ( SELECT *, ROW_NUMBER() OVER( ORDER BY SalesOrderDetailID) AS RowNumber FROM Sales.SalesOrderDetail PC) SELECT * FROM CTE_SalesOrderDetail WHERE RowNumber >= @PageNumber*@RowsPerPage+1 AND RowNumber <= (@PageNumber+1)*@RowsPerPage ORDER BY SalesOrderDetailID GO SET STATISTICS IO ON; USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 12100 SELECT * FROM Sales.SalesOrderDetail ORDER BY SalesOrderDetailID OFFSET @PageNumber*@RowsPerPage ROWS FETCH NEXT 10 ROWS ONLY GO From the resultset, it is very clear that in the earlier case, the pages read in the solution are always much higher than the new technique introduced in SQL Server 2011 even if we don’t retrieve all the data to the screen. If you carefully look at both the comparisons, the PAGE IO is much lesser in the case of the new technique introduced in SQL Server 2011 when we read the page from the beginning of the table and when we read it from the end. I consider this as a big improvement as paging is one of the most used features for the most part of the application. The solution introduced in SQL Server 2011 is very elegant because it also improves the performance of the query and, at large, the database. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQLAuthority News – Whitepaper – SQL Azure vs. SQL Server

  - by pinaldave

  SQL Server and SQL Azure are two Microsoft Products which goes almost together. There are plenty of misconceptions about SQL Azure. I have seen enough developers not planning for SQL Azure because they are not sure what exactly they are getting into. Some are confused thinking Azure is not powerful enough. I disagree and strongly urge all of you to read following white paper written and published by Microsoft. SQL Azure vs. SQL Server by Dinakar Nethi, Niraj Nagrani SQL Azure Database is a cloud-based relational database service from Microsoft. SQL Azure provides relational database functionality as a utility service. Cloud-based database solutions such as SQL Azure can provide many benefits, including rapid provisioning, cost-effective scalability, high availability, and reduced management overhead. This paper compares SQL Azure Database with SQL Server in terms of logical administration vs. physical administration, provisioning, Transact-SQL support, data storage, SSIS, along with other features and capabilities. The content of this white paper is as following: Similarities and Differences Logical Administration vs. Physical Administration Provisioning Transact-SQL Support Features and Types Key Benefits of the Service Self-Managing High Availability Scalability Familiar Development Model Relational Data Model The above summary text is taken from white paper itself. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL White Papers, SQLAuthority News, T SQL, Technology Tagged: SQL Azure

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• SQL SERVER – Find Details for Statistics of Whole Database – DMV – T-SQL Script

  - by pinaldave

  I was recently asked is there a single script which can provide all the necessary details about statistics for any database. This question made me write following script. I was initially planning to use sp_helpstats command but I remembered that this is marked to be deprecated in future. Again, using DMV is the right thing to do moving forward. I quickly wrote following script which gives a lot more information than sp_helpstats. USE AdventureWorks GO SELECT DISTINCT OBJECT_NAME(s.[object_id]) AS TableName, c.name AS ColumnName, s.name AS StatName, s.auto_created, s.user_created, s.no_recompute, s.[object_id], s.stats_id, sc.stats_column_id, sc.column_id, STATS_DATE(s.[object_id], s.stats_id) AS LastUpdated FROM sys.stats s JOIN sys.stats_columns sc ON sc.[object_id] = s.[object_id] AND sc.stats_id = s.stats_id JOIN sys.columns c ON c.[object_id] = sc.[object_id] AND c.column_id = sc.column_id JOIN sys.partitions par ON par.[object_id] = s.[object_id] JOIN sys.objects obj ON par.[object_id] = obj.[object_id] WHERE OBJECTPROPERTY(s.OBJECT_ID,'IsUserTable') = 1 AND (s.auto_created = 1 OR s.user_created = 1); If you have better script to retrieve information about statistics, please share here and I will publish it with due credit. 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 Tagged: SQL Statistics, Statistics

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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 – 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 – Guest Post by Sandip Pani – SQL Server Statistics Name and Index Creation

  - by pinaldave

  Sometimes something very small or a common error which we observe in daily life teaches us new things. SQL Server Expert Sandip Pani (winner of Joes 2 Pros Contests) has come across similar experience. Sandip has written a guest post on an error he faced in his daily work. Sandip is working for QSI Healthcare as an Associate Technical Specialist and have more than 5 years of total experience. He blogs at SQLcommitted.com and contribute in various forums. His social media hands are LinkedIn, Facebook and Twitter. Once I faced following error when I was working on performance tuning project and attempt to create an Index. Mug 1913, Level 16, State 1, Line 1 The operation failed because an index or statistics with name ‘Ix_Table1_1′ already exists on table ‘Table1′. The immediate reaction to the error was that I might have created that index earlier and when I researched it further I found the same as the index was indeed created two times. This totally makes sense. This can happen due to many reasons for example if the user is careless and executes the same code two times as well, when he attempts to create index without checking if there was index already on the object. However when I paid attention to the details of the error, I realize that error message also talks about statistics along with the index. I got curious if the same would happen if I attempt to create indexes with the same name as statistics already created. There are a few other questions also prompted in my mind. I decided to do a small demonstration of the subject and build following demonstration script. The goal of my experiment is to find out the relation between statistics and the index. Statistics is one of the important input parameter for the optimizer during query optimization process. If the query is nontrivial then only optimizer uses statistics to perform a cost based optimization to select a plan. For accuracy and further learning I suggest to read MSDN. Now let’s find out the relationship between index and statistics. We will do the experiment in two parts. i) Creating Index ii) Creating Statistics We will be using the following T-SQL script for our example. IF (OBJECT_ID('Table1') IS NOT NULL) DROP TABLE Table1 GO CREATE TABLE Table1 (Col1 INT NOT NULL, Col2 VARCHAR(20) NOT NULL) GO We will be using following two queries to check if there are any index or statistics on our sample table Table1. -- Details of Index SELECT OBJECT_NAME(OBJECT_ID) AS TableName, Name AS IndexName, type_desc FROM sys.indexes WHERE OBJECT_NAME(OBJECT_ID) = 'table1' GO -- Details of Statistics SELECT OBJECT_NAME(OBJECT_ID) TableName, Name AS StatisticsName FROM sys.stats WHERE OBJECT_NAME(OBJECT_ID) = 'table1' GO When I ran above two scripts on the table right after it was created it did not give us any result which was expected. Now let us begin our test. 1) Create an index on the table Create following index on the table. CREATE NONCLUSTERED INDEX Ix_Table1_1 ON Table1(Col1) GO Now let us use above two scripts and see their results. We can see that when we created index at the same time it created statistics also with the same name. Before continuing to next set of demo – drop the table using following script and re-create the table using a script provided at the beginning of the table. DROP TABLE table1 GO 2) Create a statistic on the table Create following statistics on the table. CREATE STATISTICS Ix_table1_1 ON Table1 (Col1) GO Now let us use above two scripts and see their results. We can see that when we created statistics Index is not created. The behavior of this experiment is different from the earlier experiment. Clean up the table setup using the following script: DROP TABLE table1 GO Above two experiments teach us very valuable lesson that when we create indexes, SQL Server generates the index and statistics (with the same name as the index name) together. Now due to the reason if we have already had statistics with the same name but not the index, it is quite possible that we will face the error to create the index even though there is no index with the same name. A Quick Check To validate that if we create statistics first and then index after that with the same name, it will throw an error let us run following script in SSMS. Make sure to drop the table and clean up our sample table at the end of the experiment. -- Create sample table CREATE TABLE TestTable (Col1 INT NOT NULL, Col2 VARCHAR(20) NOT NULL) GO -- Create Statistics CREATE STATISTICS IX_TestTable_1 ON TestTable (Col1) GO -- Create Index CREATE NONCLUSTERED INDEX IX_TestTable_1 ON TestTable(Col1) GO -- Check error /*Msg 1913, Level 16, State 1, Line 2 The operation failed because an index or statistics with name 'IX_TestTable_1' already exists on table 'TestTable'. */ -- Clean up DROP TABLE TestTable GO While creating index it will throw the following error as statistics with the same name is already created. In simple words – when we create index the name of the index should be different from any of the existing indexes and statistics. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Error Messages, SQL Index, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Statistics

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• SQL SERVER – SHRINKFILE and TRUNCATE Log File in SQL Server 2008

  - by pinaldave

  Note: Please read the complete post before taking any actions. This blog post would discuss SHRINKFILE and TRUNCATE Log File. The script mentioned in the email received from reader contains the following questionable code: “Hi Pinal, If you could remember, I and my manager met you at TechEd in Bangalore. We just upgraded to SQL Server 2008. One of our jobs failed as it was using the following code. The error was: Msg 155, Level 15, State 1, Line 1 ‘TRUNCATE_ONLY’ is not a recognized BACKUP option. The code was: DBCC SHRINKFILE(TestDBLog, 1) BACKUP LOG TestDB WITH TRUNCATE_ONLY DBCC SHRINKFILE(TestDBLog, 1) GO I have modified that code to subsequent code and it works fine. But, are there other suggestions you have at the moment? USE [master] GO ALTER DATABASE [TestDb] SET RECOVERY SIMPLE WITH NO_WAIT DBCC SHRINKFILE(TestDbLog, 1) ALTER DATABASE [TestDb] SET RECOVERY FULL WITH NO_WAIT GO Configuration of our server and system is as follows: [Removed not relevant data]“ An email like this that suddenly pops out in early morning is alarming email. Because I am a dead, busy mind, so I had only one min to reply. I wrote down quickly the following note. (As I said, it was a single-minute email so it is not completely accurate). Here is that quick email shared with all of you. “Hi Mr. DBA [removed the name] Thanks for your email. I suggest you stop this practice. There are many issues included here, but I would list two major issues: 1) From the setting database to simple recovery, shrinking the file and once again setting in full recovery, you are in fact losing your valuable log data and will be not able to restore point in time. Not only that, you will also not able to use subsequent log files. 2) Shrinking file or database adds fragmentation. There are a lot of things you can do. First, start taking proper log backup using following command instead of truncating them and losing them frequently. BACKUP LOG [TestDb] TO  DISK = N'C:\Backup\TestDb.bak' GO Remove the code of SHRINKING the file. If you are taking proper log backups, your log file usually (again usually, special cases are excluded) do not grow very big. There are so many things to add here, but you can call me on my [phone number]. Before you call me, I suggest for accuracy you read Paul Randel‘s two posts here and here and Brent Ozar‘s Post here. Kind Regards, Pinal Dave” I guess this post is very much clear to you. Please leave your comments here. As mentioned, this is a very huge subject; I have just touched a tip of the ice-berg and have tried to point to authentic knowledge. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Backup and Restore, SQL Data Storage, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – DMV – sys.dm_os_wait_stats Explanation – Wait Type – Day 3 of 28

  - by pinaldave

  The key Dynamic Management View (DMV) that helps us to understand wait stats is sys.dm_os_wait_stats; this DMV gives us all the information that we need to know regarding wait stats. However, the interpretation is left to us. This is a challenge as understanding wait stats can often be quite tricky. Anyway, we will cover few wait stats in one of the future articles. Today we will go over the basic understanding of the DMV. The Official Book OnLine Reference for DMV is over here: sys.dm_os_wait_stats. I suggest you all to refer this for all the accuracy. Following is a statement from the online book: “Specific types of wait times during query execution can indicate bottlenecks or stall points within the query. Similarly, high wait times, or wait counts server wide can indicate bottlenecks or hot spots in interaction query interactions within the server instance.” This is the statement which has inspired me to write this series. Let us first run the following statement from DMV. SELECT * FROM sys.dm_os_wait_stats ORDER BY wait_time_ms DESC GO Above statement will show us few of the columns. Here it is quick explanation of each of the column. wait_type – this is the name of the wait type. There can be three different kinds of wait types – resource, queue and external. waiting_tasks_count – this incremental counter is a good indication of frequent the wait is happening. If this number is very high, it is good indication for us to investigate that particular wait type. It is quite possible that the wait time is considerably low, but the frequency of the wait is much high. wait_time_ms – this is total wait accumulated for any type of wait. This is the total wait time and includes singal_wait_time_ms. max_wait_time_ms – this indicates the maximum wait type ever occurred for that particular wait type. Using this, one can estimate the intensity of the wait type in past. Again, it is not necessary that this max wait time will occur every time; so do not over invest yourself here. signal_wait_time_ms – this is the wait time when thread is marked as runnable and it gets to the running state. If the runnable queue is very long, you will find that this wait time becomes high. Additionally, please note that this DMV does not show current wait type or wait stats. This is cumulative view of the all the wait stats since server (instance) restarted or wait stats have been cleared. In future blog post, we will also cover two more DMVs which can be helpful to identify wait-related issues. ?sys.dm_os_waiting_tasks sys.dm_exec_requests 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, 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 – Interview Questions & Answers Needs Your Help

  - by pinaldave

  About an year ago, I had posted SQL Server related Interview Questions and Answers. It was very well received in community. I have received many comments, suggestions and emails on this subject. I am planning to upgrade the Interview Questions and Answers and take it to next level. Here, I need your help. Please your comments, suggestions, expectation or potential interview Question (along with answer) here. Your input will be very valuable. As time goes by we all learn and get better. There were few things missing at that time when those interview questions and answers were prepared, now is the time to complete the gap and make this interview questions more useful. If you know all, this Question and Answers are not for you. This are for those who is eager to learn and need help in the area. If you do not want to leave a comment, I suggest to send me email at pinal “at” SQLAuthority.com Following is the reproduction of original consolidation post for quick reference. SQL SERVER – 2008 – Interview Questions and Answers – Part 1 SQL SERVER – 2008 – Interview Questions and Answers – Part 2 SQL SERVER – 2008 – Interview Questions and Answers – Part 3 SQL SERVER – 2008 – Interview Questions and Answers – Part 4 SQL SERVER – 2008 – Interview Questions and Answers – Part 5 SQL SERVER – 2008 – Interview Questions and Answers – Part 6 SQL SERVER – 2008 – Interview Questions and Answers – Part 7 SQL SERVER – 2008 – Interview Questions and Answers – Part 8 Download SQL Server 2008 Interview Questions and Answers Complete List Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Interview Questions and Answers, SQL Query, 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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• SQL SERVER – Fundamentals of Columnstore Index

  - by pinaldave

  There are two kind of storage in database. Row Store and Column Store. Row store does exactly as the name suggests – stores rows of data on a page – and column store stores all the data in a column on the same page. These columns are much easier to search – instead of a query searching all the data in an entire row whether the data is relevant or not, column store queries need only to search much lesser number of the columns. This means major increases in search speed and hard drive use. Additionally, the column store indexes are heavily compressed, which translates to even greater memory and faster searches. I am sure this looks very exciting and it does not mean that you convert every single index from row store to column store index. One has to understand the proper places where to use row store or column store indexes. Let us understand in this article what is the difference in Columnstore type of index. Column store indexes are run by Microsoft’s VertiPaq technology. However, all you really need to know is that this method of storing data is columns on a single page is much faster and more efficient. Creating a column store index is very easy, and you don’t have to learn new syntax to create them. You just need to specify the keyword “COLUMNSTORE” and enter the data as you normally would. Keep in mind that once you add a column store to a table, though, you cannot delete, insert or update the data – it is READ ONLY. However, since column store will be mainly used for data warehousing, this should not be a big problem. You can always use partitioning to avoid rebuilding the index. A columnstore index stores each column in a separate set of disk pages, rather than storing multiple rows per page as data traditionally has been stored. The difference between column store and row store approaches is illustrated below: In case of the row store indexes multiple pages will contain multiple rows of the columns spanning across multiple pages. In case of column store indexes multiple pages will contain multiple single columns. This will lead only the columns needed to solve a query will be fetched from disk. Additionally there is good chance that there will be redundant data in a single column which will further help to compress the data, this will have positive effect on buffer hit rate as most of the data will be in memory and due to same it will not need to be retrieved. Let us see small example of how columnstore index improves the performance of the query on a large table. As a first step let us create databaseset which is large enough to show performance impact of columnstore index. The time taken to create sample database may vary on different computer based on the resources. USE AdventureWorks GO -- Create New Table CREATE TABLE [dbo].[MySalesOrderDetail]( [SalesOrderID] [int] NOT NULL, [SalesOrderDetailID] [int] NOT NULL, [CarrierTrackingNumber] [nvarchar](25) NULL, [OrderQty] [smallint] NOT NULL, [ProductID] [int] NOT NULL, [SpecialOfferID] [int] NOT NULL, [UnitPrice] [money] NOT NULL, [UnitPriceDiscount] [money] NOT NULL, [LineTotal] [numeric](38, 6) NOT NULL, [rowguid] [uniqueidentifier] NOT NULL, [ModifiedDate] [datetime] NOT NULL ) ON [PRIMARY] GO -- Create clustered index CREATE CLUSTERED INDEX [CL_MySalesOrderDetail] ON [dbo].[MySalesOrderDetail] ( [SalesOrderDetailID]) GO -- Create Sample Data Table -- WARNING: This Query may run upto 2-10 minutes based on your systems resources INSERT INTO [dbo].[MySalesOrderDetail] SELECT S1.* FROM Sales.SalesOrderDetail S1 GO 100 Now let us do quick performance test. I have kept STATISTICS IO ON for measuring how much IO following queries take. In my test first I will run query which will use regular index. We will note the IO usage of the query. After that we will create columnstore index and will measure the IO of the same. -- Performance Test -- Comparing Regular Index with ColumnStore Index USE AdventureWorks GO SET STATISTICS IO ON GO -- Select Table with regular Index SELECT ProductID, SUM(UnitPrice) SumUnitPrice, AVG(UnitPrice) AvgUnitPrice, SUM(OrderQty) SumOrderQty, AVG(OrderQty) AvgOrderQty FROM [dbo].[MySalesOrderDetail] GROUP BY ProductID ORDER BY ProductID GO -- Table 'MySalesOrderDetail'. Scan count 1, logical reads 342261, physical reads 0, read-ahead reads 0. -- Create ColumnStore Index CREATE NONCLUSTERED COLUMNSTORE INDEX [IX_MySalesOrderDetail_ColumnStore] ON [MySalesOrderDetail] (UnitPrice, OrderQty, ProductID) GO -- Select Table with Columnstore Index SELECT ProductID, SUM(UnitPrice) SumUnitPrice, AVG(UnitPrice) AvgUnitPrice, SUM(OrderQty) SumOrderQty, AVG(OrderQty) AvgOrderQty FROM [dbo].[MySalesOrderDetail] GROUP BY ProductID ORDER BY ProductID GO It is very clear from the results that query is performance extremely fast after creating ColumnStore Index. The amount of the pages it has to read to run query is drastically reduced as the column which are needed in the query are stored in the same page and query does not have to go through every single page to read those columns. If we enable execution plan and compare we can see that column store index performance way better than regular index in this case. Let us clean up the database. -- Cleanup DROP INDEX [IX_MySalesOrderDetail_ColumnStore] ON [dbo].[MySalesOrderDetail] GO TRUNCATE TABLE dbo.MySalesOrderDetail GO DROP TABLE dbo.MySalesOrderDetail GO In future posts we will see cases where Columnstore index is not appropriate solution as well few other tricks and tips of the columnstore index. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Index, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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

  - by pinaldave

  SQL Server 2012 introduces new analytical function PERCENTILE_CONT(). 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 – it is lot like finding median with percentile value. 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: You can see that I have used PERCENTILE_COUNT(0.5) in query, which is similar to finding median. Let me explain above diagram with little more explanation. The defination of median is as following: In case of Even Number of elements = In ordered list add the two digits from the middle and devide by 2 In case of Odd Numbers of elements = In ordered list select the digits from the middle I hope this example gives clear idea how PERCENTILE_CONT() works. 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 – Installing AdventureWorks Sample Database – SQL in Sixty Seconds #010 – Video

  - by pinaldave

  SQL Server has so many enhancements and features that quite often I feel like playing with various features and try out new things. I often come across situation where I want to try something new but I do not have sample data to experiment with. Also just like any sane developer I do not try any of my new experiments on production server. Additionally, when it is about new version of the SQL Server, there are cases when there is no relevant sample data even available on development server. In this kind of scenario sample database can be very much handy. Additionally, in many SQL Books and online blogs and articles there are scripts written by using AdventureWork database. The often receive request that where people can get sample database as well how to restore sample database. In this sixty seconds video we have discussed the same. You can get various resources used in this video from http://bit.ly/adw2012. More on Errors: SQL SERVER – Install Samples Database Adventure Works for SQL Server 2012 SQL SERVER – 2012 – All Download Links in Single Page – SQL Server 2012 SQLAuthority News – SQL Server 2012 – Microsoft Learning Training and Certification SQLAuthority News – Download Microsoft SQL Server 2012 RTM Now 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 Tips and Tricks, T SQL, Technology, Video

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• SQL SERVER – 2000 – DBCC SQLPERF(waitstats) – Wait Type – Day 24 of 28

  - by pinaldave

  I have received many comments, email, suggestions and motivations for my current series of wait types and wait statistics. One of the questions which I keep on receiving almost every other day is whether all of the discussions I have presented so far are also applicable to SQL Server 2000. Additionally, I receive another question asking me if wait statistics matters in SQL Server 2000. If it is, then the asker wants to know how to measure wait types for SQL Server 2000. In SQL Server, you can run the following command to get a list of all the wait types: DBCC SQLPERF(waitstats) The query above will work in SQL Server 2005/2008/R2  because of backup compatibility. As you might have noticed, I have been discussing everything keeping SQL Server 2005+ in mind, but I have given little consideration on SQL Server 2000. However, I am pretty sure that most of the suggestions I have provided are applicable to SQL Server 2000. The wait types I have been discussing mostly exist in SQL Server 2000 as well. But the difference of the 2000 version is that it gets late recent releases, but it is worth it. Wait types are very essential to measure performance bottleneck. Because of this, I do not have to state that I am big fan of them just so I could identify performance bottleneck. Please read all the post in the Wait Types and Queue series. 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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