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  • SQL SERVER – SSMS: Backup and Restore Events Report

    - by Pinal Dave
    A DBA wears multiple hats and in fact does more than what an eye can see. One of the core task of a DBA is to take backups. This looks so trivial that most developers shrug this off as the only activity a DBA might be doing. I have huge respect for DBA’s all around the world because even if they seem cool with all the scripting, automation, maintenance works round the clock to keep the business working almost 365 days 24×7, their worth is knowing that one day when the systems / HDD crashes and you have an important delivery to make. So these backup tasks / maintenance jobs that have been done come handy and are no more trivial as they might seem to be as considered by many. So the important question like: “When was the last backup taken?”, “How much time did the last backup take?”, “What type of backup was taken last?” etc are tricky questions and this report lands answers to the same in a jiffy. So the SSMS report, we are talking can be used to find backups and restore operation done for the selected database. Whenever we perform any backup or restore operation, the information is stored in the msdb database. This report can utilize that information and provide information about the size, time taken and also the file location for those operations. Here is how this report can be launched.   Once we launch this report, we can see 4 major sections shown as listed below. Average Time Taken For Backup Operations Successful Backup Operations Backup Operation Errors Successful Restore Operations Let us look at each section next. Average Time Taken For Backup Operations Information shown in “Average Time Taken For Backup Operations” section is taken from a backupset table in the msdb database. Here is the query and the expanded version of that particular section USE msdb; SELECT (ROW_NUMBER() OVER (ORDER BY t1.TYPE))%2 AS l1 ,       1 AS l2 ,       1 AS l3 ,       t1.TYPE AS [type] ,       (AVG(DATEDIFF(ss,backup_start_date, backup_finish_date)))/60.0 AS AverageBackupDuration FROM backupset t1 INNER JOIN sys.databases t3 ON ( t1.database_name = t3.name) WHERE t3.name = N'AdventureWorks2014' GROUP BY t1.TYPE ORDER BY t1.TYPE On my small database the time taken for differential backup was less than a minute, hence the value of zero is displayed. This is an important piece of backup operation which might help you in planning maintenance windows. Successful Backup Operations Here is the expanded version of this section.   This information is derived from various backup tracking tables from msdb database.  Here is the simplified version of the query which can be used separately as well. SELECT * FROM sys.databases t1 INNER JOIN backupset t3 ON (t3.database_name = t1.name) LEFT OUTER JOIN backupmediaset t5 ON ( t3.media_set_id = t5.media_set_id) LEFT OUTER JOIN backupmediafamily t6 ON ( t6.media_set_id = t5.media_set_id) WHERE (t1.name = N'AdventureWorks2014') ORDER BY backup_start_date DESC,t3.backup_set_id,t6.physical_device_name; The report does some calculations to show the data in a more readable format. For example, the backup size is shown in KB, MB or GB. I have expanded first row by clicking on (+) on “Device type” column. That has shown me the path of the physical backup file. Personally looking at this section, the Backup Size, Device Type and Backup Name are critical and are worth a note. As mentioned in the previous section, this section also has the Duration embedded inside it. Backup Operation Errors This section of the report gets data from default trace. You might wonder how. One of the event which is tracked by default trace is “ErrorLog”. This means that whatever message is written to errorlog gets written to default trace file as well. Interestingly, whenever there is a backup failure, an error message is written to ERRORLOG and hence default trace. This section takes advantage of that and shows the information. We can read below message under this section, which confirms above logic. No backup operations errors occurred for (AdventureWorks2014) database in the recent past or default trace is not enabled. Successful Restore Operations This section may not be very useful in production server (do you perform a restore of database?) but might be useful in the development and log shipping secondary environment, where we might be interested to see restore operations for a particular database. Here is the expanded version of the section. To fill this section of the report, I have restored the same backups which were taken to populate earlier sections. Here is the simplified version of the query used to populate this output. USE msdb; SELECT * FROM restorehistory t1 LEFT OUTER JOIN restorefile t2 ON ( t1.restore_history_id = t2.restore_history_id) LEFT OUTER JOIN backupset t3 ON ( t1.backup_set_id = t3.backup_set_id) WHERE t1.destination_database_name = N'AdventureWorks2014' ORDER BY restore_date DESC,  t1.restore_history_id,t2.destination_phys_name Have you ever looked at the backup strategy of your key databases? Are they in sync and do we have scope for improvements? Then this is the report to analyze after a week or month of maintenance plans running in your database. Do chime in with what are the strategies you are using in your environments. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL Tagged: SQL Reports

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  • SQL SERVER – Concurrency Basics – Guest Post by Vinod Kumar

    - by pinaldave
    This guest post is by Vinod Kumar. Vinod Kumar has worked with SQL Server extensively since joining the industry over a decade ago. Working on various versions from SQL Server 7.0, Oracle 7.3 and other database technologies – he now works with the Microsoft Technology Center (MTC) as a Technology Architect. Let us read the blog post in Vinod’s own voice. Learning is always fun when it comes to SQL Server and learning the basics again can be more fun. I did write about Transaction Logs and recovery over my blogs and the concept of simplifying the basics is a challenge. In the real world we always see checks and queues for a process – say railway reservation, banks, customer supports etc there is a process of line and queue to facilitate everyone. Shorter the queue higher is the efficiency of system (a.k.a higher is the concurrency). Every database does implement this using checks like locking, blocking mechanisms and they implement the standards in a way to facilitate higher concurrency. In this post, let us talk about the topic of Concurrency and what are the various aspects that one needs to know about concurrency inside SQL Server. Let us learn the concepts as one-liners: Concurrency can be defined as the ability of multiple processes to access or change shared data at the same time. The greater the number of concurrent user processes that can be active without interfering with each other, the greater the concurrency of the database system. Concurrency is reduced when a process that is changing data prevents other processes from reading that data or when a process that is reading data prevents other processes from changing that data. Concurrency is also affected when multiple processes are attempting to change the same data simultaneously. Two approaches to managing concurrent data access: Optimistic Concurrency Model Pessimistic Concurrency Model Concurrency Models Pessimistic Concurrency Default behavior: acquire locks to block access to data that another process is using. Assumes that enough data modification operations are in the system that any given read operation is likely affected by a data modification made by another user (assumes conflicts will occur). Avoids conflicts by acquiring a lock on data being read so no other processes can modify that data. Also acquires locks on data being modified so no other processes can access the data for either reading or modifying. Readers block writer, writers block readers and writers. Optimistic Concurrency Assumes that there are sufficiently few conflicting data modification operations in the system that any single transaction is unlikely to modify data that another transaction is modifying. Default behavior of optimistic concurrency is to use row versioning to allow data readers to see the state of the data before the modification occurs. Older versions of the data are saved so a process reading data can see the data as it was when the process started reading and not affected by any changes being made to that data. Processes modifying the data is unaffected by processes reading the data because the reader is accessing a saved version of the data rows. Readers do not block writers and writers do not block readers, but, writers can and will block writers. Transaction Processing A transaction is the basic unit of work in SQL Server. Transaction consists of SQL commands that read and update the database but the update is not considered final until a COMMIT command is issued (at least for an explicit transaction: marked with a BEGIN TRAN and the end is marked by a COMMIT TRAN or ROLLBACK TRAN). Transactions must exhibit all the ACID properties of a transaction. ACID Properties Transaction processing must guarantee the consistency and recoverability of SQL Server databases. Ensures all transactions are performed as a single unit of work regardless of hardware or system failure. A – Atomicity C – Consistency I – Isolation D- Durability Atomicity: Each transaction is treated as all or nothing – it either commits or aborts. Consistency: ensures that a transaction won’t allow the system to arrive at an incorrect logical state – the data must always be logically correct.  Consistency is honored even in the event of a system failure. Isolation: separates concurrent transactions from the updates of other incomplete transactions. SQL Server accomplishes isolation among transactions by locking data or creating row versions. Durability: After a transaction commits, the durability property ensures that the effects of the transaction persist even if a system failure occurs. If a system failure occurs while a transaction is in progress, the transaction is completely undone, leaving no partial effects on data. Transaction Dependencies In addition to supporting all four ACID properties, a transaction might exhibit few other behaviors (known as dependency problems or consistency problems). Lost Updates: Occur when two processes read the same data and both manipulate the data, changing its value and then both try to update the original data to the new value. The second process might overwrite the first update completely. Dirty Reads: Occurs when a process reads uncommitted data. If one process has changed data but not yet committed the change, another process reading the data will read it in an inconsistent state. Non-repeatable Reads: A read is non-repeatable if a process might get different values when reading the same data in two reads within the same transaction. This can happen when another process changes the data in between the reads that the first process is doing. Phantoms: Occurs when membership in a set changes. It occurs if two SELECT operations using the same predicate in the same transaction return a different number of rows. Isolation Levels SQL Server supports 5 isolation levels that control the behavior of read operations. Read Uncommitted All behaviors except for lost updates are possible. Implemented by allowing the read operations to not take any locks, and because of this, it won’t be blocked by conflicting locks acquired by other processes. The process can read data that another process has modified but not yet committed. When using the read uncommitted isolation level and scanning an entire table, SQL Server can decide to do an allocation order scan (in page-number order) instead of a logical order scan (following page pointers). If another process doing concurrent operations changes data and move rows to a new location in the table, the allocation order scan can end up reading the same row twice. Also can happen if you have read a row before it is updated and then an update moves the row to a higher page number than your scan encounters later. Performing an allocation order scan under Read Uncommitted can cause you to miss a row completely – can happen when a row on a high page number that hasn’t been read yet is updated and moved to a lower page number that has already been read. Read Committed Two varieties of read committed isolation: optimistic and pessimistic (default). Ensures that a read never reads data that another application hasn’t committed. If another transaction is updating data and has exclusive locks on data, your transaction will have to wait for the locks to be released. Your transaction must put share locks on data that are visited, which means that data might be unavailable for others to use. A share lock doesn’t prevent others from reading but prevents them from updating. Read committed (snapshot) ensures that an operation never reads uncommitted data, but not by forcing other processes to wait. SQL Server generates a version of the changed row with its previous committed values. Data being changed is still locked but other processes can see the previous versions of the data as it was before the update operation began. Repeatable Read This is a Pessimistic isolation level. Ensures that if a transaction revisits data or a query is reissued the data doesn’t change. That is, issuing the same query twice within a transaction cannot pickup any changes to data values made by another user’s transaction because no changes can be made by other transactions. However, this does allow phantom rows to appear. Preventing non-repeatable read is a desirable safeguard but cost is that all shared locks in a transaction must be held until the completion of the transaction. Snapshot Snapshot Isolation (SI) is an optimistic isolation level. Allows for processes to read older versions of committed data if the current version is locked. Difference between snapshot and read committed has to do with how old the older versions have to be. It’s possible to have two transactions executing simultaneously that give us a result that is not possible in any serial execution. Serializable This is the strongest of the pessimistic isolation level. Adds to repeatable read isolation level by ensuring that if a query is reissued rows were not added in the interim, i.e, phantoms do not appear. Preventing phantoms is another desirable safeguard, but cost of this extra safeguard is similar to that of repeatable read – all shared locks in a transaction must be held until the transaction completes. In addition serializable isolation level requires that you lock data that has been read but also data that doesn’t exist. Ex: if a SELECT returned no rows, you want it to return no. rows when the query is reissued. This is implemented in SQL Server by a special kind of lock called the key-range lock. Key-range locks require that there be an index on the column that defines the range of values. If there is no index on the column, serializable isolation requires a table lock. Gets its name from the fact that running multiple serializable transactions at the same time is equivalent of running them one at a time. Now that we understand the basics of what concurrency is, the subsequent blog posts will try to bring out the basics around locking, blocking, deadlocks because they are the fundamental blocks that make concurrency possible. Now if you are with me – let us continue learning for SQL Server Locking Basics. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Concurrency

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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 – Solution – Puzzle – SELECT * vs SELECT COUNT(*)

    - by pinaldave
    Earlier I have published Puzzle Why SELECT * throws an error but SELECT COUNT(*) does not. This question have received many interesting comments. Let us go over few of the answers, which are valid. Before I start the same, let me acknowledge Rob Farley who has not only answered correctly very first but also started interesting conversation in the same thread. The usual question will be what is the right answer. I would like to point to official Microsoft Connect Items which discusses the same. RGarvao https://connect.microsoft.com/SQLServer/feedback/details/671475/select-test-where-exists-select tiberiu utan http://connect.microsoft.com/SQLServer/feedback/details/338532/count-returns-a-value-1 Rob Farley count(*) is about counting rows, not a particular column. It doesn’t even look to see what columns are available, it’ll just count the rows, which in the case of a missing FROM clause, is 1. “select *” is designed to return columns, and therefore barfs if there are none available. Even more odd is this one: select ‘blah’ where exists (select *) You might be surprised at the results… Koushik The engine performs a “Constant scan” for Count(*) where as in the case of “SELECT *” the engine is trying to perform either Index/Cluster/Table scans. amikolaj When you query ‘select * from sometable’, SQL replaces * with the current schema of that table. With out a source for the schema, SQL throws an error. so when you query ‘select count(*)’, you are counting the one row. * is just a constant to SQL here. Check out the execution plan. Like the description states – ‘Scan an internal table of constants.’ You could do ‘select COUNT(‘my name is adam and this is my answer’)’ and get the same answer. Netra Acharya SELECT * Here, * represents all columns from a table. So it always looks for a table (As we know, there should be FROM clause before specifying table name). So, it throws an error whenever this condition is not satisfied. SELECT COUNT(*) Here, COUNT is a Function. So it is not mandetory to provide a table. Check it out this: DECLARE @cnt INT SET @cnt = COUNT(*) SELECT @cnt SET @cnt = COUNT(‘x’) SELECT @cnt Naveen Select 1 / Select ‘*’ will return 1/* as expected. Select Count(1)/Count(*) will return the count of result set of select statement. Count(1)/Count(*) will have one 1/* for each row in the result set of select statement. Select 1 or Select ‘*’ result set will contain only 1 result. so count is 1. Where as “Select *” is a sysntax which expects the table or equauivalent to table (table functions, etc..). It is like compilation error for that query. Ramesh Hi Friends, Count is an aggregate function and it expects the rows (list of records) for a specified single column or whole rows for *. So, when we use ‘select *’ it definitely give and error because ‘*’ is meant to have all the fields but there is not any table and without table it can only raise an error. So, in the case of ‘Select Count(*)’, there will be an error as a record in the count function so you will get the result as ’1'. Try using : Select COUNT(‘RAMESH’) and think there is an error ‘Must specify table to select from.’ in place of ‘RAMESH’ Pinal : If i am wrong then please clarify this. Sachin Nandanwar Any aggregate function expects a constant or a column name as an expression. DO NOT be confused with * in an aggregate function.The aggregate function does not treat it as a column name or a set of column names but a constant value, as * is a key word in SQL. You can replace any value instead of * for the COUNT function.Ex Select COUNT(5) will result as 1. The error resulting from select * is obvious it expects an object where it can extract the result set. I sincerely thank you all for wonderful conversation, I personally enjoyed it and I am sure all of you have the same feeling. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: CodeProject, Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • Linq-to-sql Compiled Query returns object NOT belonging to submitted DataContext ?

    - by Vladimir Kojic
    Compiled query: public static class Machines { public static readonly Func<OperationalDataContext, short, Machine> QueryMachineById = CompiledQuery.Compile((OperationalDataContext db, short machineID) => db.Machines.Where(m => m.MachineID == machineID).SingleOrDefault() ); public static Machine GetMachineById(IUnitOfWork unitOfWork, short id) { Machine machine; // Old code (working) //var machineRepository = unitOfWork.GetRepository<Machine>(); //machine = machineRepository.Find(m => m.MachineID == id).SingleOrDefault(); // New code (making problems) machine = QueryMachineById(unitOfWork.DataContext, id); return machine; } It looks like compiled query is returning result from another data context [TestMethod] public void GetMachinesTest() { using (var unitOfWork = IoC.Get<IUnitOfWork>()) { // Compile Query var machine = Machines.GetMachineById(unitOfWork, 3); } using (var unitOfWork = IoC.Get<IUnitOfWork>()) { var machineRepository = unitOfWork.GetRepository<Machine>(); // Get From Repository var machineFromRepository = machineRepository.Find(m => m.MachineID == 2).SingleOrDefault(); var machine = Machines.GetMachineById(unitOfWork, 2); VerifyHuskyHostMachine(machineFromRepository, 2, "Machine 2", "222222", "H400RS", "MachineIconB.xaml", false, true, LicenseType.Licensed, InterfaceType.HuskyHostV2, "10.0.97.2:8080", "10.0.97.2", 8080, "4.0"); VerifyHuskyHostMachine(machine, 2, "Machine 2", "222222", "H400RS", "MachineIconB.xaml", false, true, LicenseType.Licensed, InterfaceType.HuskyHostV2, "10.0.97.2:8080", "10.0.97.2", 8080, "4.0"); Assert.AreSame(machineFromRepository, machine); // FAIL } } If I run other (complex) unit tests I'm getting as expected: An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. Another Important information is that this test is under TransactionScope! UPDATE: It looks like next link is describing similar problem (is this bug solved ?): http://social.msdn.microsoft.com/Forums/en-US/linqprojectgeneral/thread/9bcffc2d-794e-4c4a-9e3e-cdc89dad0e38

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  • How do I break down MySQL query results into categories, each with a specific number of rows?

    - by Mel
    Hello, Problem: I want to list n number of games from each genre (order not important) The following MySQL query resides inside a ColdFusion function. It is meant to list all games under a platform (for example, list all PS3 games; list all Xbox 360 games; etc...). The variable for PlatformID is passed through the URL. I have 9 genres, and I would like to list 10 games from each genre. SELECT games.GameID AS GameID, games.GameReleaseDate AS rDate, titles.TitleName AS tName, titles.TitleShortDescription AS sDesc, genres.GenreName AS gName, platforms.PlatformID, platforms.PlatformName AS pName, platforms.PlatformAbbreviation AS pAbbr FROM (((games join titles on((games.TitleID = titles.TitleID))) join genres on((genres.GenreID = games.GenreID))) join platforms on((platforms.PlatformID = games.PlatformID))) WHERE (games.PlatformID = '#ARGUMENTS.PlatformID#') ORDER BY GenreName ASC, GameReleaseDate DESC Once the query results come back I group them in ColdFusion as follows: <cfoutput query="ListGames" group="gName"> (first loop which lists genres) #ListGames.gName# <cfoutput> (nested loop which lists games) #ListGames.tName# </cfoutput> </cfoutput> The problem is that I only want 10 games from each genre to be listed. If I place a "limit" of 50 in the SQL, I will get ~ 50 games of the same genre (depending on how much games of that genre there are). The second issue is I don't want the overload of querying the database for all games when each person will only look at a few. What is the correct way to do this? Many thanks!

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  • SQL SERVER – SQLServer Quiz 2011 – Do you know your execution plan – Two questions – One Answer

    - by pinaldave
    My friend Jacob Sebastian has SQL Server Quiz 2011 launched. This time when he asked me to come up with quiz question – I wanted to come up with something which is new and make participant to think about it. After carefully thinking I come with question which I really like to solve myself. Here is the details: 1) Using Single table only Once in Single SELECT statement generate execution plan which have JOIN operator. Explain the reason for the same. 2) Using Single table only Once in Single SELECT statement generate execution plan which have parallelism operator. Explain the reason for the same. Bonus: Create a single query which satisfy both of the above statement. To answer this question and win exciting gifts please visit the SQL Server Quiz website. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – Script to Find First Day of Current Month

    - by Pinal Dave
    Earlier I wrote a blog post about SQL SERVER – Query to Find First and Last Day of Current Month and it is a very popular post. In this post, I convert the datetime to Varchar and later on use it. However, SQL Expert Michael Usov has made a good point suggesting that it is not always a good idea to convert datetime to any other date format as it is quite possible that we may need it the value in the datetime format for other operation. He has suggested a very quick solution where we can get the first day of the current month with or without time value and keep them with datatype datetime. Here is the simple script for the same. -- first day of month -- with time zeroed out SELECT CAST(DATEADD(DAY,-DAY(GETDATE())+1, CAST(GETDATE() AS DATE)) AS DATETIME) -- with time as it was SELECT DATEADD(DAY,-DAY(GETDATE())+1, CAST(GETDATE() AS DATETIME)) Here is the resultset: Reference: Pinal Dave (http://blog.SQLAuthority.com)Filed under: PostADay, SQL, SQL Authority, SQL DateTime, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • SQL SERVER – SSIS Parameters in Parent-Child ETL Architectures – Notes from the Field #040

    - by Pinal Dave
    [Notes from Pinal]: SSIS is very well explored subject, however, there are so many interesting elements when we read, we learn something new. A similar concept has been Parent-Child ETL architecture’s relationship in SSIS. Linchpin People are database coaches and wellness experts for a data driven world. In this 40th episode of the Notes from the Fields series database expert Tim Mitchell (partner at Linchpin People) shares very interesting conversation related to how to understand SSIS Parameters in Parent-Child ETL Architectures. In this brief Notes from the Field post, I will review the use of SSIS parameters in parent-child ETL architectures. A very common design pattern used in SQL Server Integration Services is one I call the parent-child pattern.  Simply put, this is a pattern in which packages are executed by other packages.  An ETL infrastructure built using small, single-purpose packages is very often easier to develop, debug, and troubleshoot than large, monolithic packages.  For a more in-depth look at parent-child architectures, check out my earlier blog post on this topic. When using the parent-child design pattern, you will frequently need to pass values from the calling (parent) package to the called (child) package.  In older versions of SSIS, this process was possible but not necessarily simple.  When using SSIS 2005 or 2008, or even when using SSIS 2012 or 2014 in package deployment mode, you would have to create package configurations to pass values from parent to child packages.  Package configurations, while effective, were not the easiest tool to work with.  Fortunately, starting with SSIS in SQL Server 2012, you can now use package parameters for this purpose. In the example I will use for this demonstration, I’ll create two packages: one intended for use as a child package, and the other configured to execute said child package.  In the parent package I’m going to build a for each loop container in SSIS, and use package parameters to pass in a value – specifically, a ClientID – for each iteration of the loop.  The child package will be executed from within the for each loop, and will create one output file for each client, with the source query and filename dependent on the ClientID received from the parent package. Configuring the Child and Parent Packages When you create a new package, you’ll see the Parameters tab at the package level.  Clicking over to that tab allows you to add, edit, or delete package parameters. As shown above, the sample package has two parameters.  Note that I’ve set the name, data type, and default value for each of these.  Also note the column entitled Required: this allows me to specify whether the parameter value is optional (the default behavior) or required for package execution.  In this example, I have one parameter that is required, and the other is not. Let’s shift over to the parent package briefly, and demonstrate how to supply values to these parameters in the child package.  Using the execute package task, you can easily map variable values in the parent package to parameters in the child package. The execute package task in the parent package, shown above, has the variable vThisClient from the parent package mapped to the pClientID parameter shown earlier in the child package.  Note that there is no value mapped to the child package parameter named pOutputFolder.  Since this parameter has the Required property set to False, we don’t have to specify a value for it, which will cause that parameter to use the default value we supplied when designing the child pacakge. The last step in the parent package is to create the for each loop container I mentioned earlier, and place the execute package task inside it.  I’m using an object variable to store the distinct client ID values, and I use that as the iterator for the loop (I describe how to do this more in depth here).  For each iteration of the loop, a different client ID value will be passed into the child package parameter. The final step is to configure the child package to actually do something meaningful with the parameter values passed into it.  In this case, I’ve modified the OleDB source query to use the pClientID value in the WHERE clause of the query to restrict results for each iteration to a single client’s data.  Additionally, I’ll use both the pClientID and pOutputFolder parameters to dynamically build the output filename. As shown, the pClientID is used in the WHERE clause, so we only get the current client’s invoices for each iteration of the loop. For the flat file connection, I’m setting the Connection String property using an expression that engages both of the parameters for this package, as shown above. Parting Thoughts There are many uses for package parameters beyond a simple parent-child design pattern.  For example, you can create standalone packages (those not intended to be used as a child package) and still use parameters.  Parameter values may be supplied to a package directly at runtime by a SQL Server Agent job, through the command line (via dtexec.exe), or through T-SQL. Also, you can also have project parameters as well as package parameters.  Project parameters work in much the same way as package parameters, but the parameters apply to all packages in a project, not just a single package. Conclusion Of the numerous advantages of using catalog deployment model in SSIS 2012 and beyond, package parameters are near the top of the list.  Parameters allow you to easily share values from parent to child packages, enabling more dynamic behavior and better code encapsulation. If you want me to take a look at your server and its settings, or if your server is facing any issue we can Fix Your SQL Server. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: Notes from the Field, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • Why would a SQL query JOIN on the same table twice with the same condition?

    - by Scott Leis
    I'm working on changes to a SQL Server v8 database developed by someone else, and have found something that seems (based on my limited SQL knowledge) strange and pointless. One of the views has a query that does a LEFT OUTER JOIN twice on the same table with the same condition. Is there any reason for doing this? The query is below. See the second- and third-last lines that both join the "te_SDE_Survey" table on the "SDE_ID" field. Also note these lines set two different aliases for the table, and both aliases are used in the SELECT part of the query. SELECT vs.SLMS_Code, vs.Retail_Date, vs.TagNo, vs.Rego, vs.Model, vs.Company, vs.AccountType, viqdp.SDE_ID, bd.Debit_Date, isu.Survey_Date, CASE WHEN isu.Q6 IS NOT NULL THEN isu.Q6 ELSE CASE WHEN returned_surveys.survey_date IS NULL THEN CASE WHEN (viqdp.expiryDate < getdate() AND cs.sup1 IS NULL AND cs.sup2 IS NULL AND cs.sup3 IS NULL AND cs.sup5 IS NULL AND cs.sup8 IS NULL AND cs.sup9 IS NULL) THEN 'E' WHEN (viqdp.expiryDate < getdate() AND cs.sup1 = 'F' AND cs.sup2 = 'F' AND cs.sup3 = 'F' AND cs.sup5 = 'F' AND cs.sup8 = 'F' AND cs.sup9 = 'F') THEN 'E' WHEN cs.sup1 = 'T' THEN 'S' WHEN cs.sup2 = 'T' AND (cs.sup8 = 'F' AND cs.sup9 = 'F') THEN 'D' WHEN cs.sup3 = 'T' AND (cs.sup8 = 'F' AND cs.sup9 = 'F') THEN 'D' WHEN cs.sup5 = 'T' AND (cs.sup8 = 'F' AND cs.sup9 = 'F') THEN 'D' WHEN cs.sup8 = 'T' AND (cs.sup2 = 'F' AND cs.sup3 = 'F' AND cs.sup5 = 'F') THEN 'E' WHEN cs.sup9 = 'T' AND (cs.sup2 = 'F' AND cs.sup3 = 'F' AND cs.sup5 = 'F') THEN 'E' WHEN (cs.sup8 = 'T' OR cs.sup9 = 'T') AND (cs.sup2 = 'T' OR cs.sup3 = 'T' OR cs.sup5 = 'T') THEN 'S' END WHEN (tey.survey_expire_method = 'pre2008') THEN CASE WHEN (datediff(month, viqdp.generate_date, returned_surveys.survey_date) 1) THEN 'E' END WHEN (tey.survey_expire_method = 'expiryDateColumn') THEN CASE WHEN (returned_surveys.survey_date viqdp.expiryDate) THEN 'E' END END END AS score_or_exclusion_status, CASE WHEN (bd.explanation IS NULL) THEN '' ELSE bd.explanation END AS explanation, tey.te_Year FROM dbo.te_Vehicle_Sale vs INNER JOIN dbo.te_Year tey ON vs.Retail_Date = tey.Start_Date AND vs.Retail_Date <= tey.End_Date LEFT OUTER JOIN dbo.Bad_Data bd ON vs.TagNo = bd.TagNo LEFT OUTER JOIN dbo.te_Vehicle_SDESurvey viqdp ON vs.TagNo = viqdp.TagNo LEFT OUTER JOIN dbo.te_SDE_Survey isu ON viqdp.SDE_ID = isu.SDE_ID LEFT OUTER JOIN dbo.te_SDE_Survey returned_surveys ON viqdp.SDE_ID = returned_surveys.SDE_ID LEFT OUTER JOIN dbo.te_SDE_Contact_Suppression cs ON viqdp.SDE_ID = cs.SDE_ID

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  • SQL SERVER – Video – Performance Improvement in Columnstore Index

    - by pinaldave
    I earlier wrote an article about SQL SERVER – Fundamentals of Columnstore Index and it got very well accepted in community. However, one of the suggestion I keep on receiving for that article is that many of the reader wanted to see columnstore index in the action but they were not able to do that. Some of the readers did not install SQL Server 2012 or some did not have good machine to recreate the big table involved in the demo. For the same reason, I have created small video for that. I have written two more article on columstore index. Please read them as followup to the video: SQL SERVER – How to Ignore Columnstore Index Usage in Query SQL SERVER – Updating Data in A Columnstore Index Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Index, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video

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  • SQL SERVER – Number-Crunching with SQL Server – Exceed the Functionality of Excel

    - by Pinal Dave
    Imagine this. Your users have developed an Excel spreadsheet that extracts data from your SQL Server database, manipulates that data through the use of Excel formulas and, possibly, some VBA code which is then used to calculate P&L, hedging requirements or even risk numbers. Management comes to you and tells you that they need to get rid of the spreadsheet and that the results of the spreadsheet calculations need to be persisted on the database. SQL Server has a very small set of functions for analyzing data. Excel has hundreds of functions for analyzing data, with many of them focused on specific financial and statistical calculations. Is it even remotely possible that you can use SQL Server to replace the complex calculations being done in a spreadsheet? Westclintech has developed a library of functions that match or exceed the functionality of Excel’s functions and contains many functions that are not available in EXCEL. Their XLeratorDB library of functions contains over 700 functions that can be incorporated into T-SQL statements. XLeratorDB takes advantage of the SQL CLR architecture introduced in SQL Server 2005. SQL CLR permits managed code to be compiled into the database and run alongside built-in SQL Server functions like COUNT or SUM. The Westclintech developers have taken advantage of this architecture to bring robust analytical functions to the database. In our hypothetical spreadsheet, let’s assume that our users are using the YIELD function and that the data are extracted from a table in our database called BONDS. Here’s what the spreadsheet might look like. We go to column G and see that it contains the following formula. Obviously, SQL Server does not offer a native YIELD function. However, with XLeratorDB we can replicate this calculation in SQL Server with the following statement: SELECT *, wct.YIELD(CAST(GETDATE() AS date),Maturity,Rate,Price,100,Frequency,Basis) AS YIELD FROM BONDS This produces the following result. This illustrates one of the best features about XLeratorDB; it is so easy to use. Since I knew that the spreadsheet was using the YIELD function I could use the same function with the same calling structure to do the calculation in SQL Server. I didn’t need to know anything at all about the mechanics of calculating the yield on a bond. It was pretty close to cut and paste. In fact, that’s one way to construct the SQL. Just copy the function call from the cell in the spreadsheet and paste it into SMS and change the cell references to column names. I built the SQL for this query by starting with this. SELECT * ,YIELD(TODAY(),B2,C2,D2,100,E2,F2) FROM BONDS I then changed the cell references to column names. SELECT * --,YIELD(TODAY(),B2,C2,D2,100,E2,F2) ,YIELD(TODAY(),Maturity,Rate,Price,100,Frequency,Basis) FROM BONDS Finally, I replicated the TODAY() function using GETDATE() and added the schema name to the function name. SELECT * --,YIELD(TODAY(),B2,C2,D2,100,E2,F2) --,YIELD(TODAY(),Maturity,Rate,Price,100,Frequency,Basis) ,wct.YIELD(GETDATE(),Maturity,Rate,Price,100,Frequency,Basis) FROM BONDS Then I am able to execute the statement returning the results seen above. The XLeratorDB libraries are heavy on financial, statistical, and mathematical functions. Where there is an analog to an Excel function, the XLeratorDB function uses the same naming conventions and calling structure as the Excel function, but there are also hundreds of additional functions for SQL Server that are not found in Excel. You can find the functions by opening Object Explorer in SQL Server Management Studio (SSMS) and expanding the Programmability folder under the database where the functions have been installed. The  Functions folder expands to show 3 sub-folders: Table-valued Functions; Scalar-valued functions, Aggregate Functions, and System Functions. You can expand any of the first three folders to see the XLeratorDB functions. Since the wct.YIELD function is a scalar function, we will open the Scalar-valued Functions folder, scroll down to the wct.YIELD function and and click the plus sign (+) to display the input parameters. The functions are also Intellisense-enabled, with the input parameters displayed directly in the query tab. The Westclintech website contains documentation for all the functions including examples that can be copied directly into a query window and executed. There are also more one hundred articles on the site which go into more detail about how some of the functions work and demonstrate some of the extensive business processes that can be done in SQL Server using XLeratorDB functions and some T-SQL. XLeratorDB is organized into libraries: finance, statistics; math; strings; engineering; and financial options. There is also a windowing library for SQL Server 2005, 2008, and 2012 which provides functions for calculating things like running and moving averages (which were introduced in SQL Server 2012), FIFO inventory calculations, financial ratios and more, without having to use triangular joins. To get started you can download the XLeratorDB 15-day free trial from the Westclintech web site. It is a fully-functioning, unrestricted version of the software. If you need more than 15 days to evaluate the software, you can simply download another 15-day free trial. XLeratorDB is an easy and cost-effective way to start adding sophisticated data analysis to your SQL Server database without having to know anything more than T-SQL. Get XLeratorDB Today and Now! Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL Tagged: Excel

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  • SQL SERVER – Weekly Series – Memory Lane – #006

    - by pinaldave
    Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2006 This was my very first year of blogging so I was every day learning something new. As I have said many times, that blogging was never an intention. I had really not understood what exactly I am working on or beginning when I was beginning blogging in 2006. I had never knew that my life was going to change forever, once I started blogging. When I look back all of this year, I am happy that we are here together. 2007 IT Outsourcing to India – Top 10 Reasons Companies Outsource Outsourcing is about trust, collaboration and success. Helping other countries in need has been always the course of mankind, outsourcing is nothing different then that. With information technology and process improvements increasing the complexity, costs and skills required to accomplish routine tasks as well as challenging complex tasks, companies are outsourcing such tasks to providers who have the expertise to perform them at lower costs , with greater value and quality outcome. UDF – Remove Duplicate Chars From String This was a very interesting function I wrote in my early career. I am still using this function when I have to remove duplicate chars from strings. I have yet to come across a scenario where it does not work so I keep on using it till today. Please leave a comment if there is any better solution to this problem. FIX : Error : 3702 Cannot drop database because it is currently in use This is a very generic error when DROP Database is command is executed and the database is not dropped. The common mistake user is kept the connection open with this database and trying to drop the database. The database cannot be dropped if there is any other connection open along with it. It is always a good idea to take database in single user mode before dropping it. Here is the quick tutorial regarding how to bring the database in single user mode: Using T-SQL | Using SSMS. 2008 Install SQL Server 2008 – How to Upgrade to SQL Server 2008 – Installation Tutorial This was indeed one of the most popular articles in SQL Server 2008. Lots of people wanted to learn how to install SQL SErver 2008 but they were facing various issues while installation. I build this tutorial which becomes reference points for many. Default Collation of SQL Server 2008 What is the collation of SQL Server 2008 default installations? I often see this question confusing many experienced developers as well. Well the answer is in following image. Ahmedabad SQL Server User Group Meeting – November 2008 User group meetings are fun, now a days I am going to User Group meetings every week but there was a case when I have been just a beginner on this subject. The bug of the community was caught on me years ago when I started to present in Ahmedabad and Gandhinagar SQ LServer User Groups. 2009 Validate an XML document in TSQL using XSD My friend Jacob Sebastian wrote an excellent article on the subject XML and XSD. Because of the ‘eXtensible’ nature of XML (eXtensible Markup Language), often there is a requirement to restrict and validate the content of an XML document to a pre-defined structure and values. XSD (XML Schema Definition Language) is the W3C recommended language for describing and validating XML documents. SQL Server implements XSD as XML Schema Collections. Star Join Query Optimization At present, when queries are sent to very large databases, millions of rows are returned. Also the users have to go through extended query response times when joining multiple tables are involved with such queries. ‘Star Join Query Optimization’ is a new feature of SQL Server 2008 Enterprise Edition. This mechanism uses bitmap filtering for improving the performance of some types of queries by the effective retrieval of rows from fact tables. 2010 These puzzles are very interesting and intriguing – there was lots of interest on this subject. If you have free time this weekend. You may want to try them out. SQL SERVER – Challenge – Puzzle – Usage of FAST Hint (Solution)  SQL SERVER – Puzzle – Challenge – Error While Converting Money to Decimal (Solution)  SQL SERVER – Challenge – Puzzle – Why does RIGHT JOIN Exists (Open)  Additionally, I had great fun presenting SQL Server Performance Tuning seminar at fantastic locations in Hyderabad. Installing AdventeWorks Database This has been the most popular request I have received on my blog. Here is the quick video about how one can install AdventureWorks. 2011 Effect of SET NOCOUNT on @@ROWCOUNT There was an interesting incident once while I was presenting a session. I wrote a code and suddenly 10 hands went up in the air.  This was a bit surprise to me as I do not know why they all got alerted. I assumed that there should be something wrong with either project, screen or my display. However the real reason was very interesting – I suggest you read the complete blog post to understand this interesting scenario. Error: Deleting Offline Database and Creating the Same Name This is very interesting because once a user deletes the offline database the MDF and LDF file still exists and if the user attempts to create a new database with the same name it will give error. I found this very interesting and the blog explains the concept very quickly. Have you ever faced a similar situation? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – How to Force New Cardinality Estimation or Old Cardinality Estimation

    - by Pinal Dave
    After reading my initial two blog posts on New Cardinality Estimation, I received quite a few questions. Once I receive this question, I felt I should have clarified it earlier few things when I started to write about cardinality. Before continuing this blog, if you have not read it before I suggest you read following two blog posts. SQL SERVER – Simple Demo of New Cardinality Estimation Features of SQL Server 2014 SQL SERVER – Cardinality Estimation and Performance – SQL in Sixty Seconds #072 Q: Does new cardinality will improve performance of all of my queries? A: Remember, there is no 0 or 1 logic when it is about estimation. The general assumption is that most of the queries will be benefited by new cardinality estimation introduced in SQL Server 2014. That is why the generic advice is to set the compatibility level of the database to 120, which is for SQL Server 2014. Q: Is it possible that after changing cardinality estimation to new logic by setting the value to compatibility level to 120, I get degraded performance for few queries? A: Yes, it is possible. However, the number of the queries where this impact should be very less. Q: Can I still run my database in older compatibility level and force few queries to newer cardinality estimation logic? If yes, How? A: Yes, you can do that. You will need to force your query with trace flag 2312 to use newer cardinality estimation logic. USE AdventureWorks2014 GO -- Old Cardinality Estimation ALTER DATABASE AdventureWorks2014 SET COMPATIBILITY_LEVEL = 110 GO -- Using New Cardinality Estimation SELECT [AddressID],[AddressLine1],[City] FROM [Person].[Address] OPTION(QUERYTRACEON 2312);; -- Using Old Cardinality Estimation SELECT [AddressID],[AddressLine1],[City] FROM [Person].[Address]; GO Q: Can I run my database in newer compatibility level and force few queries to older cardinality estimation logic? If yes, How? A: Yes, you can do that. You will need to force your query with trace flag 9481 to use newer cardinality estimation logic. USE AdventureWorks2014 GO -- NEW Cardinality Estimation ALTER DATABASE AdventureWorks2014 SET COMPATIBILITY_LEVEL = 120 GO -- Using New Cardinality Estimation SELECT [AddressID],[AddressLine1],[City] FROM [Person].[Address]; -- Using Old Cardinality Estimation SELECT [AddressID],[AddressLine1],[City] FROM [Person].[Address] OPTION(QUERYTRACEON 9481); GO I guess, I have covered most of the questions so far I have received. If I have missed any questions, please send me again and I will include the same. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • SQL SERVER – A Puzzle Part 3 – Fun with SEQUENCE in SQL Server 2012 – Guess the Next Value

    - by pinaldave
    Before continuing this blog post – please read the two part of the SEQUENCE Puzzle here A Puzzle – Fun with SEQUENCE in SQL Server 2012 – Guess the Next Value and A Puzzle Part 2 – Fun with SEQUENCE in SQL Server 2012 – Guess the Next Value Where we played a simple guessing game about predicting next value. The answers the of puzzle is shared on the blog posts as a comment. Now here is the next puzzle based on yesterday’s puzzle. I recently shared the puzzle of the blog post on local user group and it was appreciated by attendees. First execute the script which I have written here. Today’s script is bit different than yesterday’s script as well it will require you to do some service related activities. I suggest you try this on your personal computer’s test environment when no one is working on it. Do not attempt this on production server as it will for sure get you in trouble. The purpose to learn how sequence behave during the unexpected shutdowns and services restarts. Now guess what will be the next value as requested in the query. USE AdventureWorks2012 GO -- Create sequence CREATE SEQUENCE dbo.SequenceID AS BIGINT START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 500 CYCLE CACHE 100; GO -- Following will return 1 SELECT next value FOR dbo.SequenceID; ------------------------------------- -- simulate server crash by restarting service -- do not attempt this on production or any server in use ------------------------------------ -- Following will return ??? SELECT next value FOR dbo.SequenceID; -- Clean up DROP SEQUENCE dbo.SequenceID; GO Once the server is restarted what will be the next value for SequenceID. We can learn interesting trivia’s about this new feature of SQL Server using this puzzle. Hint: Pay special attention to the difference between new number and earlier number. Can you see the same number in the definition of the CREATE SEQUENCE? Bonus Question: How to avoid the behavior demonstrated in above mentioned query. Does it have any effect of performance? I suggest you try to attempt to answer this question without running this code in SQL Server 2012. You can restart SQL Server using command prompt as well. I will follow up of the answer in comments below. Recently my friend Vinod Kumar wrote excellent blog post on SQL Server 2012: Using SEQUENCE, you can head over there for learning sequence in details. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Weekly Series – Memory Lane – #037

    - by Pinal Dave
    Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 Convert Text to Numbers (Integer) – CAST and CONVERT If table column is VARCHAR and has all the numeric values in it, it can be retrieved as Integer using CAST or CONVERT function. List All Stored Procedure Modified in Last N Days If SQL Server suddenly start behaving in un-expectable behavior and if stored procedure were changed recently, following script can be used to check recently modified stored procedure. If a stored procedure was created but never modified afterwards modified date and create a date for that stored procedure are same. Count Duplicate Records – Rows Validate Field For DATE datatype using function ISDATE() We always checked DATETIME field for incorrect data type. One of the user input date as 30/2/2007. The date was sucessfully inserted in the temp table but while inserting from temp table to final table it crashed with error. We had now task to validate incorrect date value before we insert in final table. Jr. Developer asked me how can he do that? We check for incorrect data type (varchar, int, NULL) but this is incorrect date value. Regular expression works fine with them because of mm/dd/yyyy format. 2008 Find Space Used For Any Particular Table It is very simple to find out the space used by any table in the database. Two Convenient Features Inline Assignment – Inline Operations Here is the script which does both – Inline Assignment and Inline Operation DECLARE @idx INT = 0 SET @idx+=1 SELECT @idx Introduction to SPARSE Columns SPARSE column are better at managing NULL and ZERO values in SQL Server. It does not take any space in database at all. If column is created with SPARSE clause with it and it contains ZERO or NULL it will be take lesser space then regular column (without SPARSE clause). SP_CONFIGURE – Displays or Changes Global Configuration Settings If advanced settings are not enabled at configuration level SQL Server will not let user change the advanced features on server. Authorized user can turn on or turn off advance settings. 2009 Standby Servers and Types of Standby Servers Standby Server is a type of server that can be brought online in a situation when Primary Server goes offline and application needs continuous (high) availability of the server. There is always a need to set up a mechanism where data and objects from primary server are moved to secondary (standby) server. BLOB – Pointer to Image, Image in Database, FILESTREAM Storage When it comes to storing images in database there are two common methods. I had previously blogged about the same subject on my visit to Toronto. With SQL Server 2008, we have a new method of FILESTREAM storage. However, the answer on when to use FILESTREAM and when to use other methods is still vague in community. 2010 Upper Case Shortcut SQL Server Management Studio I select the word and hit CTRL+SHIFT+U and it SSMS immediately changes the case of the selected word. Similar way if one want to convert cases to lower case, another short cut CTRL+SHIFT+L is also available. The Self Join – Inner Join and Outer Join Self Join has always been a noteworthy case. It is interesting to ask questions about self join in a room full of developers. I often ask – if there are three kinds of joins, i.e.- Inner Join, Outer Join and Cross Join; what type of join is Self Join? The usual answer is that it is an Inner Join. However, the reality is very different. Parallelism – Row per Processor – Row per Thread – Thread 0  If you look carefully in the Properties window or XML Plan, there is “Thread 0?. What does this “Thread 0” indicate? Well find out from the blog post. How do I Learn and How do I Teach The blog post has raised three very interesting questions. How do you learn? How do you teach? What are you learning or teaching? Let me try to answer the same. 2011 SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 7 of 31 What are Different Types of Locks? What are Pessimistic Lock and Optimistic Lock? When is the use of UPDATE_STATISTICS command? What is the Difference between a HAVING clause and a WHERE clause? What is Connection Pooling and why it is Used? What are the Properties and Different Types of Sub-Queries? What are the Authentication Modes in SQL Server? How can it be Changed? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 8 of 31 Which Command using Query Analyzer will give you the Version of SQL Server and Operating System? What is an SQL Server Agent? Can a Stored Procedure call itself or a Recursive Stored Procedure? How many levels of SP nesting is possible? What is Log Shipping? Name 3 ways to get an Accurate Count of the Number of Records in a Table? What does it mean to have QUOTED_IDENTIFIER ON? What are the Implications of having it OFF? What is the Difference between a Local and a Global Temporary Table? What is the STUFF Function and How Does it Differ from the REPLACE Function? What is PRIMARY KEY? What is UNIQUE KEY Constraint? What is FOREIGN KEY? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 9 of 31 What is CHECK Constraint? What is NOT NULL Constraint? What is the difference between UNION and UNION ALL? What is B-Tree? How to get @@ERROR and @@ROWCOUNT at the Same Time? What is a Scheduled Job or What is a Scheduled Task? What are the Advantages of Using Stored Procedures? What is a Table Called, if it has neither Cluster nor Non-cluster Index? What is it Used for? Can SQL Servers Linked to other Servers like Oracle? What is BCP? When is it Used? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 10 of 31 What Command do we Use to Rename a db, a Table and a Column? What are sp_configure Commands and SET Commands? How to Implement One-to-One, One-to-Many and Many-to-Many Relationships while Designing Tables? What is Difference between Commit and Rollback when Used in Transactions? What is an Execution Plan? When would you Use it? How would you View the Execution Plan? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 11 of 31 What is Difference between Table Aliases and Column Aliases? Do they Affect Performance? What is the difference between CHAR and VARCHAR Datatypes? What is the Difference between VARCHAR and VARCHAR(MAX) Datatypes? What is the Difference between VARCHAR and NVARCHAR datatypes? Which are the Important Points to Note when Multilanguage Data is Stored in a Table? How to Optimize Stored Procedure Optimization? What is SQL Injection? How to Protect Against SQL Injection Attack? How to Find Out the List Schema Name and Table Name for the Database? What is CHECKPOINT Process in the SQL Server? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 12 of 31 How does Using a Separate Hard Drive for Several Database Objects Improves Performance Right Away? How to Find the List of Fixed Hard Drive and Free Space on Server? Why can there be only one Clustered Index and not more than one? What is Difference between Line Feed (\n) and Carriage Return (\r)? Is It Possible to have Clustered Index on Separate Drive From Original Table Location? What is a Hint? How to Delete Duplicate Rows? Why the Trigger Fires Multiple Times in Single Login? 2012 CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis Shortcut key is CTRL+SHIFT+]. This key can be very useful when dealing with multiple subqueries, CTE or query with multiple parentheses. When exercised this shortcut key it selects T-SQL code between two parentheses. Monday Morning Puzzle – Query Returns Results Sometimes but Not Always I am beginner with SQL Server. I have one query, it sometime returns a result and sometime it does not return me the result. Where should I start looking for a solution and what kind of information I should send to you so you can help me with solving. I have no clue, please guide me. Remove Debug Button in SSMS – SQL in Sixty Seconds #020 – Video Effect of Case Sensitive Collation on Resultset Collation is a very interesting concept but I quite often see it is heavily neglected. I have seen developer and DBA looking for a workaround to fix collation error rather than understanding if the side effect of the workaround. Switch Between Two Parenthesis using Shortcut CTRL+] Earlier this week I wrote a blog post about CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis, I received quite a lot of positive feedback from readers. If you are a regular reader of the blog post, you must be aware that I appreciate the learning shared by readers. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • How do I break down MySQL query results into categories, each with a specific number of rows?

    - by Mel
    Hello, Problem: I want to list n number of games from each genre (order not important) The following MySQL query resides inside a ColdFusion function. It is meant to list all games under a platform (for example, list all PS3 games; list all Xbox 360 games; etc...). The variable for PlatformID is passed through the URL. I have 9 genres, and I would like to list 10 games from each genre. SELECT games.GameID AS GameID, games.GameReleaseDate AS rDate, titles.TitleName AS tName, titles.TitleShortDescription AS sDesc, genres.GenreName AS gName, platforms.PlatformID, platforms.PlatformName AS pName, platforms.PlatformAbbreviation AS pAbbr FROM (((games join titles on((games.TitleID = titles.TitleID))) join genres on((genres.GenreID = games.GenreID))) join platforms on((platforms.PlatformID = games.PlatformID))) WHERE (games.PlatformID = '#ARGUMENTS.PlatformID#') ORDER BY GenreName ASC, GameReleaseDate DESC Once the query results come back I group them in ColdFusion as follows: <cfoutput query="ListGames" group="gName"> (first loop which lists genres) #ListGames.gName# <cfoutput> (nested loop which lists games) #ListGames.tName# </cfoutput> </cfoutput> The problem is that I only want 10 games from each genre to be listed. If I place a "limit" of 50 in the SQL, I will get ~ 50 games of the same genre (depending on how much games of that genre there are). The second issue is I don't want the overload of querying the database for all games when each person will only look at a few. What is the correct way to do this? Many thanks!

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  • Does query plan optimizer works well with joined/filtered table-valued functions?

    - by smoothdeveloper
    In SQLSERVER 2005, I'm using table-valued function as a convenient way to perform arbitrary aggregation on subset data from large table (passing date range or such parameters). I'm using theses inside larger queries as joined computations and I'm wondering if the query plan optimizer work well with them in every condition or if I'm better to unnest such computation in my larger queries. Does query plan optimizer unnest table-valued functions if it make sense? If it doesn't, what do you recommend to avoid code duplication that would occur by manually unnesting them? If it does, how do you identify that from the execution plan? code sample: create table dbo.customers ( [key] uniqueidentifier , constraint pk_dbo_customers primary key ([key]) ) go /* assume large amount of data */ create table dbo.point_of_sales ( [key] uniqueidentifier , customer_key uniqueidentifier , constraint pk_dbo_point_of_sales primary key ([key]) ) go create table dbo.product_ranges ( [key] uniqueidentifier , constraint pk_dbo_product_ranges primary key ([key]) ) go create table dbo.products ( [key] uniqueidentifier , product_range_key uniqueidentifier , release_date datetime , constraint pk_dbo_products primary key ([key]) , constraint fk_dbo_products_product_range_key foreign key (product_range_key) references dbo.product_ranges ([key]) ) go . /* assume large amount of data */ create table dbo.sales_history ( [key] uniqueidentifier , product_key uniqueidentifier , point_of_sale_key uniqueidentifier , accounting_date datetime , amount money , quantity int , constraint pk_dbo_sales_history primary key ([key]) , constraint fk_dbo_sales_history_product_key foreign key (product_key) references dbo.products ([key]) , constraint fk_dbo_sales_history_point_of_sale_key foreign key (point_of_sale_key) references dbo.point_of_sales ([key]) ) go create function dbo.f_sales_history_..snip.._date_range ( @accountingdatelowerbound datetime, @accountingdateupperbound datetime ) returns table as return ( select pos.customer_key , sh.product_key , sum(sh.amount) amount , sum(sh.quantity) quantity from dbo.point_of_sales pos inner join dbo.sales_history sh on sh.point_of_sale_key = pos.[key] where sh.accounting_date between @accountingdatelowerbound and @accountingdateupperbound group by pos.customer_key , sh.product_key ) go -- TODO: insert some data -- this is a table containing a selection of product ranges declare @selectedproductranges table([key] uniqueidentifier) -- this is a table containing a selection of customers declare @selectedcustomers table([key] uniqueidentifier) declare @low datetime , @up datetime -- TODO: set top query parameters . select saleshistory.customer_key , saleshistory.product_key , saleshistory.amount , saleshistory.quantity from dbo.products p inner join @selectedproductranges productrangeselection on p.product_range_key = productrangeselection.[key] inner join @selectedcustomers customerselection on 1 = 1 inner join dbo.f_sales_history_..snip.._date_range(@low, @up) saleshistory on saleshistory.product_key = p.[key] and saleshistory.customer_key = customerselection.[key] I hope the sample makes sense. Much thanks for your help!

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  • SQL SERVER – Detect Virtual Log Files (VLF) in LDF

    - by pinaldave
    In one of the recent training engagements, I was asked if it true that there are multiple small log files in the large log file (LDF). I found this question very interesting as the answer is yes. Multiple small Virtual Log Files commonly known as VLFs together make an LDF file. The writing of the VLF is sequential and resulting in the writing of the LDF file is sequential as well. This leads to another talk that one does not need more than one log file in most cases. However, in short, you can use following DBCC command to know how many Virtual Log Files or VLFs are present in your log file. DBCC LOGINFO You can find the result of above query to something as displayed in following image. You can see the column which is marked as 2 which means it is active VLF and the one with 0 which is inactive VLF. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Big Data – Buzz Words: What is NewSQL – Day 10 of 21

    - by Pinal Dave
    In yesterday’s blog post we learned the importance of the relational database. In this article we will take a quick look at the what is NewSQL. What is NewSQL? NewSQL stands for new scalable and high performance SQL Database vendors. The products sold by NewSQL vendors are horizontally scalable. NewSQL is not kind of databases but it is about vendors who supports emerging data products with relational database properties (like ACID, Transaction etc.) along with high performance. Products from NewSQL vendors usually follow in memory data for speedy access as well are available immediate scalability. NewSQL term was coined by 451 groups analyst Matthew Aslett in this particular blog post. On the definition of NewSQL, Aslett writes: “NewSQL” is our shorthand for the various new scalable/high performance SQL database vendors. We have previously referred to these products as ‘ScalableSQL‘ to differentiate them from the incumbent relational database products. Since this implies horizontal scalability, which is not necessarily a feature of all the products, we adopted the term ‘NewSQL’ in the new report. And to clarify, like NoSQL, NewSQL is not to be taken too literally: the new thing about the NewSQL vendors is the vendor, not the SQL. In other words - NewSQL incorporates the concepts and principles of Structured Query Language (SQL) and NoSQL languages. It combines reliability of SQL with the speed and performance of NoSQL. Categories of NewSQL There are three major categories of the NewSQL New Architecture – In this framework each node owns a subset of the data and queries are split into smaller query to sent to nodes to process the data. E.g. NuoDB, Clustrix, VoltDB MySQL Engines – Highly Optimized storage engine for SQL with the interface of MySQ Lare the example of such category. E.g. InnoDB, Akiban Transparent Sharding – This system automatically split database across multiple nodes. E.g. Scalearc  Summary In simple words – NewSQL is kind of database following relational database principals and provides scalability like NoSQL. Tomorrow In tomorrow’s blog post we will discuss about the Role of Cloud Computing in Big Data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • SQL SERVER – Template Browser – A Very Important and Useful Feature of SSMS

    - by pinaldave
    Let me start today’s blog post with a direction question. How many of you have ever used Template Browser? Template Browser is a very important and useful feature of SQL Server Management Studio (SSMS). Every time when I am talking about SQL Server there is always someone comes up with the question, why there is no step by step procedure included in SSMS for features. Honestly every time I get this question, the question I ask back is How many of you have ever used Template Browser? I think the answer to this question is most of the time either no or we have not heard of the feature. One of the people asked me back – have you ever written about it on your blog? I have not yet written about it. Basically there is nothing much to write about it. It is pretty straight forward feature, like any other feature and it is indeed difficult to elaborate. However, I will try to give a quick introduction to this feature. Templates are like a quick cheat sheet or quick reference. Templates are available to create objects like databases, tables, views, indexes, stored procedures, triggers, statistics, and functions. Templates are also available for Analysis Services as well. The template scripts contain parameters to help you customize the code. You can Replace Template Parameters dialog box to insert values into the script. Additionally users can create new custom templates as well with folder structure. To open a template from Template Explorer Go to View menu >> Template Explorer or type CTRL+ALT+L. You will find a list of categories click on any category and expand the folder structure. For our sample example let us expand Index Folder. In this folder you will notice the various T-SQL Scripts. These scripts can be opened by double click or can be dragged to editor area and modified as needed. Sample template is now available in the query editor area with all the necessary parameter place folder. You can replace the same parameter by typing either CTRL+SHIFT+M or by going to Query Menu >> Specify Values for Template Parameters. In this screen it will show  Specify Values for Template Parameters dialog box, accept the value or replace it with a new value. This will now get your script ready to go. Check it one more time and change the script to fit your requirement. I personally use template explorer for two things. First one is obviously for templates but the hidden one and an important one is for learning new features and T-SQL commands. There is so much to learn and so little time. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology

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  • Did You Know? More online seminars!

    - by Kalen Delaney
    I am in Tucson again, having just recorded two more online workshops to be broadcast by SSWUG. We haven't set the dates yet, but we are thinking about offering a special package deal for the two of them. The topics really are related and I think they would work well together. They are both on aspects of Query Processing. The first was on how to interpret Query Plans and is an introduction to the topic. However, it only includes a discussion of how SQL Server actually processes your queries. For example,...(read more)

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  • SQL SERVER – Retrieving Random Rows from Table Using NEWID()

    - by pinaldave
    I have previously written about how to get random rows from SQL Server. SQL SERVER – Generate A Single Random Number for Range of Rows of Any Table – Very interesting Question from Reader SQL SERVER – Random Number Generator Script – SQL Query However, I have not blogged about following trick before. Let me share the trick here as well. You can generate random scripts using following methods as well. USE AdventureWorks2012 GO -- Method 1 SELECT TOP 100 * FROM Sales.SalesOrderDetail ORDER BY NEWID() GO -- Method 2 SELECT TOP 100 * FROM Sales.SalesOrderDetail ORDER BY CHECKSUM(NEWID()) GO You will notice that using NEWID() in the ORDER BY will return random rows in the result set. How many of you knew this trick? You can run above script multiple times and it will give random rows every single time. Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • C#.Net - using LDAP

    - by archit
    I have a small problem regarding the LDAP... Is it possible to retrieve all the MAC_ID's of the entire system that is connected a domain, or does the Schema Master saves the MAC_ID's of all the system that is connected in the domain

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