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  • Windows - CPU power management APIs

    - by iulianchira
    What APIs are provided by Windows for CPU power management (I'm interested in CPU frequency scaling, setting min and max CPU frequency - similar to what you can do in Control Panel in power plans, but in a programmatic way). I'm also interested in .Net APIs.

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  • MDX Studio download #mdx #ssas

    - by Marco Russo (SQLBI)
    Short version: the latest available version of MDX Studio can be downloaded from http://www.sqlbi.com/tools/mdx-studio/ Long version: Last week Stacia Misner twitted that the online version of MDX Studio was no longer available. It was hosted on http://mdx.mosha.com. It was a sad news, and it is also not good that nobody is maintaining the desktop version of MDX Studio. The latest release is the 0.4.14 and as I am writing it is still available on a SkyDrive link provided by Mosha Pasumansky, who wrote MDX Studio. Mosha does not work in Microsoft now and the entire BI community hopes that somebody will continue its work on this product. Unfortunately, it cannot be published on CodePlex because of some IP restrictions. Only bad news? Well, I hope no. The first good news is that MDX Studio also works with Analysis Services 2012 in Multidimensional mode. The second news is that, after having checked that we can do that, we created a web page on SQLBI web site to download the latest available release of MDX Studio. I hope it will be necessary to update it in the future, by now it is just a way to simplify the finding and download of this precious tool, and to grant that it will not disappear in case the current SkyDrive using to host the download would be discontinued, like it happened to the MDX Studio online version. Now a question to the BI Community: I know that there was some content available regarding tutorial on MDX Studio. I’d like to gather it and to put all in a single place. If you have such content, please contact me directly writing to marco (dot) russo (at) sqlbi [dot] com. Thanks!

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  • Different Open Source Document Management systems

    - by DJ
    HI all, Could anyone suggest some good Web based Open source Document Management systems ,other than WSS My requirements are To share pdfs/word docs/excel/access files etc Total 50 files in total of about approx 2MB each, which are updated regularly With aroung 30 users accessing them based on their rights. I would like to know if any other DMS better than WSS available. Thanks for the info.

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  • Upgrading from 2005 to R2

    - by DavidWimbush
    We're about to take the plunge and upgrade our servers from SQL 2005 to SQL 2008 R2. Real world accounts of people upgrading to R2 are a bit hard to find so I thought it might be useful to blog what happens. (I don't count marketing 'case studies' that just say stuff like "The process was effortless and the upgrade will pay for itself by the end the week.") We're using the database engine, Analysis Services and Reporting Services so upgrading by a major version number was looking a bit daunting. I wasn't expecting much trouble on the engine side of things but, as most of the action in 2008 and R2 appears to have been on the Reporting and BI front, I expected to have quite a bit of work to do. But our testing so far has been one nice surprise after another: The 2005 backups restore cleanly onto R2. R2's BI Studio upgraded the Reporting and Analysis Services solutions without any issues. The cubes all deployed and processed just fine. R2 BI Studio interacts fine with TFS 2008 version control. I'll blog some more as things develop.  

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  • SQL SERVER – SQL in Sixty Seconds – Last Three Episodes – Need Your Opinion

    - by Pinal Dave
    I have been blogging for almost 7 years and building video content for around 2 years. After spending so much time on blogging and creating video, I have got the quite a good idea what people would like to read and what people like to watch. However, there is one thing, which I am constantly struggling after almost a year and I would like to get your opinion about it. Though, this may look very simple to you but it is very crucial to me and I would like to know your opinion about it. I have been building video almost every week for my SQL in Sixty Seconds series and it has been quite popular. So far on my YouTube Channel there are over 2600 subscribers and over 250K views. Here is my problem – there are about 50+ videos on SQL in Sixty Seconds Series but the not every video is popular. There are a few videos which are extremely popular and there are videos which are absolutely struggling to get even single view. I have yet not figured out what people would love to watch on this channel. I noticed lots of people watching various videos but hardly anyone leaving comments or suggestions. At the end of the blog posts associated with the SQL in Sixty Seconds, I always ask which video people would love to watch, but I get a very low response over there too. What I wonder is that why such a low engagement of viewers/readers on the video blog posts where as the channel is success and lots of people are watching the video? What do you think I should change in my video to increase the engagement? Here are my last three videos from SQL in Sixty Seconds channel and I would like to know your feedback. Remove Cached Login from SSMS Connect Dialog – SQL in Sixty Seconds #049 RESEED Identity Column in Database Table – SQL in Sixty Seconds #051 Puzzle SET ANSI_NULLS and Resultset – SQL in Sixty Seconds #052  The feedback which I will like the most will for sure get a special surprise gift for me. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video

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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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  • C# memory management: unsafe keyword and pointers

    - by Alerty
    What are the consequences (positive/negative) of using the unsafe keyword in C# to use pointers? For example, what becomes of garbage collection, what are the performance gains/losses, what are the performance gains/losses compared to other languages manual memory management, what are the dangers, in which situation is it really justifiable to make use of this language feature... ?

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  • T-SQL Tuesday #006: Tiger/Line Spatial Data

    - by Mike C
    This month’s T-SQL Tuesday post is about LOB data http://sqlblog.com/blogs/michael_coles/archive/2010/05/03/t-sql-tuesday-006-what-about-blob.aspx . For this one I decided to post a sample Tiger/Line SQL database I use all the time in live demos. For those who aren't familiar with it, Tiger/Line data is a dataset published by the U.S. Census Bureau . Tiger/Line has a lot of nice detailed geospatial data down to a very detailed level. It actually goes from the U.S. state level all the way down to...(read more)

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  • Project management with bug tracking integrated

    - by guytom
    Hi, Can someone recommend a hosted solution that answers the following requirements (I have seen other questions but none with these specific requests): Project management with tasks, wiki, milestones Bug tracking integrated Collaborative - suitable for working with external developers Subversion integration I know Jira but it seems to be too complex and lacks on the collaboration Thanks

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  • SQL SERVER – Inviting Ideas for SQL in Sixty Seconds – 12/12/12

    - by pinaldave
    Today is 12/12/12 – I am not sure when will I write this kind of date again – maybe never. This opportunity comes once in a lifetime when we have the same date, month and year all have same digit. December 12th is one of the most fantastic day in my personal life. Four years ago, this day I got married to my wife – Nupur Dave.  Here are photos of our wedding (Dec 12, 2008). Here is a very interesting photo of myself earlier this year. It is not photoshoped or modified photo. The only modification I have done here is to add arrow and speech bubble. Every Wednesday I tried to put one SQL in Sixty Seconds Video. The journey has been fantastic and so far I have put a total of 35 SQL in Sixty Seconds Video. The goal of the video is to learn something in 1 minute. In our daily life we are all very busy and hardly have time for anything. No matter how much we are busy – we all have one minute of time. Sometime we wait for a minute in elevators, at the escalator, at a coffee shop, or just waiting for our phone reboot. Today is a fantastic day – 12/12/12. Let me invite all of you submits SQL in Sixty Seconds idea. If I like your idea and create a sixty second video over it – you will win surprise learning material from me. There are two very simple rules of the contest: - I should have not have already recorded the tip. The tip should be descriptive. Do not just suggest to cover “Performance Tuning” or “How to Create Index” or “More of reporting services”. The tip should have around 100 words of description explaining SQL Tip. The contest is open forever. The winner will be announced whenever I use the tip to convert to video. If I use your tip, I will for sure mention in the blog post that it is inspired from your suggestion. Meanwhile, do not forget to subscribe YouTube Channel. Here are my latest three videos from SQL in Sixty Seconds. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: About Me, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video

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

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

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  • Looking for a PHP based user management system

    - by dade
    I am presently looking for a user management system in PHP which can easily be integrated and built on. I have googled for it and i have two or three already on the list to try out, but then again i want the benefit of personal recommendation based on usage and experience with a solution. So if you know of any that has worked for you in time past, i would really appreciate if you can recommend. Thanks!

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  • Have SSIS' differing type systems ever caused you problems?

    - by jamiet
    One thing that has always infuriated me about SSIS is the fact that every package has three different type systems; to give you an idea of what I am talking about consider the following: The SSIS dataflow's type system is made up of types called DT_*  (e.g. DT_STR, DT_I4) The SSIS variable type system is based on .Net datatypes (e.g. String, Int32) The types available for Execute SQL Task's parameters are based on something else - I don't exactly know what (e.g. VARCHAR, LONG) Speaking euphemistically ... this is not an optimum situation (were I not speaking euphemistically I would be a lot ruder) and hence I have submitted a suggestion to Connect at [SSIS] Consolidate three type systems into one requesting that it be remedied. This accompanying blog post is not however a request for votes (though that would be nice); the reason is actually subtler than that. Let me explain. I have been submitting bugs and suggestions pertaining to SSIS for years and have, so far, submitted over 200 Connect items. If that experience has taught me anything it is this - Connect items are not generally actioned because they are considered "nice to have". No, SSIS Connect items get actioned because they cause customers grief and if I am perfectly honest I must admit that, other than being a bit gnarly, SSIS' three type system architecture has never knowingly caused me any significant problems. The reason for this blog post is to ask if any reader out there has ever encountered any problems on account of SSIS' three type systems or have you, like me, never found them to be a problem? Errors or performance degredation caused by implicit type conversions would, I believe, present a strong case for getting this situation remedied in a future version of SSIS so if you HAVE encountered such problems I would encourage you to leave a comment on the Connect submission accordingly. Let me know in the comments too - I would be interested to hear others' opinions on this. @Jamiet

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  • SQL SERVER – Solution – 2 T-SQL Puzzles – Display Star and Shortest Code to Display 1

    - by pinaldave
    Earlier on this blog we had asked two puzzles. The response from all of you is nothing but Amazing. I have received 350+ responses. Many are valid and many were indeed something I had not thought about it. I strongly suggest you read all the puzzles and their answers here - trust me if you start reading the comments you will not stop till you read every single comment. Seriously trust me on it. Personally I have learned a lot from it. Let us recap the puzzles here quickly. Puzzle 1: Why following code when executed in SSMS displays result as a * (Star)? SELECT CAST(634 AS VARCHAR(2)) Puzzle 2: Write the shortest code that produces results as 1 without using any numbers in the select statement. Bonus Q: How many different Operating System (OS) NuoDB support? As I mentioned earlier the participation was nothing but Amazing. I will write about the winners and the best answers in short time. Meanwhile I will give to the point answers to above puzzles. Solution 1: When you convert character or binary expressions (char, nchar, nvarchar, varchar,binary, or varbinary) to an expression of a different data type, data can be truncated, only partially displayed, or an error is returned because the result is too short to display. Conversions to char, varchar, nchar, nvarchar, binary, and varbinary are truncated, except for the conversions shown in the following table. Reference of the text and table from MSDN. Solution 2: The shortest code to produce answer 1 : SELECT EXP($) or SELECT COS($) or SELECT DAY($) When SELECT $ it gives us the result as 0.00 and the EXP of the same is 1. I believe it is pretty neat. There were plenty other answers but this was the shortest. Another shorter answer would be PRINT EXP($) but no one has proposed that as in original Question I have explicitly mentioned SELECT in the original question. Bonus Answer: 5 OS: Windows, MacOS, Linux, Solaris, Joyent SmartOS Reference Please do read every single comment here. Do leave a comment which one do you think is the best comment out of all the comments. Meanwhile if there is a better solution and I have missed it do let me know as we still have time to correct it. I will be selecting the winner before the weekend as I am going through each and every of 350 comment. I will be selecting the best comments along with the winning comment. If our selection matches – one of you may still win something cool.  Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology Tagged: NuoDB

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  • Smart defaults [SSDT]

    - by jamiet
    I’ve just discovered a new, somewhat hidden, feature in SSDT that I didn’t know about and figured it would be worth highlighting here because I’ll bet not many others know it either; the feature is called Smart Defaults. It gets around the problem of adding a NOT NULLable column to an existing table that has got data in it – previous to SSDT you would need to define a DEFAULT constraint however it does feel rather cumbersome to create an object purely for the purpose of pushing through a deployment – that’s the situation that Smart Defaults is meant to alleviate. The Smart Defaults option exists in the advanced section of a Publish Profile file: The description of the setting is “Automatically provides a default value when updating a table that contains data with a column that does not allow null values”, in other words checking that option will cause SSDT to insert an arbitrary default value into your newly created NON NULLable column. In case you’re wondering how it does it, here’s how: SSDT creates a DEFAULT CONSTRAINT at the same time as the column is created and then immediately removes that constraint: ALTER TABLE [dbo].[T1]    ADD [C1] INT NOT NULL,         CONSTRAINT [SD_T1_1df7a5f76cf44bb593506d05ff9a1e2b] DEFAULT 0 FOR [C1];ALTER TABLE [dbo].[T1] DROP CONSTRAINT [SD_T1_1df7a5f76cf44bb593506d05ff9a1e2b]; You can then update the value as appropriate in a Post-Deployment script. Pretty cool! On the downside, you can only specify this option for the whole project, not for an individual table or even an individual column – I’m not sure that I’d want to turn this on for an entire project as it could hide problems that a failed deployment would highlight, in other words smart defaults could be seen to be “papering over the cracks”. If you think that should be improved go and vote (and leave a comment) at [SSDT] Allow us to specify Smart defaults per table or even per column. @Jamiet

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  • Always use dtexec.exe to test performance of your dataflows. No exceptions.

    - by jamiet
    Earlier this evening I posted a blog post entitled Investigation: Can different combinations of components effect Dataflow performance? where I compared the performance of three different dataflows all working to the same overall goal. I wanted to make one last point related to the results but I thought it warranted a blog post all of its own. Here is a screenshot of one of the dataflows that I was testing: Pretty complicated I’m sure you’ll agree. Now, when I executed this dataflow in the test it was executing in ~19seconds however in that case I was executing using the command-line tool dtexec. I also tried executing inside the BIDS development environment and in that case it took much longer – 139seconds. That’s more than seven times as long. The point I want to make is very simple. If you are testing your dataflows for performance please use dtexec. Nothing else will suffice. @Jamiet

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  • What could cause my LAN Pings be greater than 100ms?

    - by James Holland
    I have 2 servers (Both: Windows Server 2008, Dual Xeon 2.8Ghz, 32GB RAM, 8 x 15k SAS Drives). One of them is a DC / Web server / Exchange Server, the other is a SQL Server (2008). I have a 48 port Netgear GS748T Gigabit switch. When I ping from server to server, I get ping times <1ms, great, but when I ping from a PC, I get varying pings from the occasional <1ms to 500ms!! If I log into either server and look at Task Manager, CPU usage peaks at 20%, memory usage is 100%, but I am led to believe this is normal as Exchange will just use as much as you have, and release it when requested. Network usage peaks at 1%. I really don't understand how the ping can vary that much. I know I am giving very little info, but this is all I know, I apologise, but can anyone help? In response to question, I have pinged by both IP address and hostname, no difference in ping times.

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  • The Oracle Cash Management Secret Very Few Customers Know About

    - by Theresa Hickman
    Did you know that Oracle Cash Management has a robust positioning feature? I had no idea. I was under the mistaken impression that Oracle Cash Management only did bank statement reconciliations. It seems I am not alone. In fact, many Oracle Financials customers are also not aware of this even though it is delivered for free with the Oracle Financials license. Even better, last week, Oracle released an enhancement to Oracle Cash Management for Release 12 that will greatly help customers with their cash positioning needs. As we all know, credit is tight these days. Companies need better visibility of their cash and other liquidity positions to make better use of their cash resources. Today, many customers are managing their cash positions manually using spreadsheets. We also hear how many of them are maintaining larger than normal balances in numerous bank accounts because they just do not have the visibility, and therefore the comfort they need. Although spreadsheets may work in the short-term, they are not the best way to manage your cash positions for the long-term especially if you have dozens, or even hundreds of bank and brokerage accounts. Also, spreadsheets are a lot more risky because they can be overwritten, deleted, difficult to audit, etc. With the newly enhanced positioning feature in Oracle Cash Management, customers can manage their daily cash positions using an excel-like interface that is very flexible and user-configurable. You can link the worksheet to an unlimited number of bank accounts to automatically retrieve your opening balances, the current/intra-day cash inflows and outflows, as well as your expected cash flows from your Fx, Investment and Debt positions if you have Oracle's Treasury module . Oracle Cash Management also has direct integration with Oracle Receivables, Oracle Payables, and Payroll, which adds to the comprehensive picture of what's happening with your organizations' cash in real-time. Here's a screen shot of what the cash positioning page looks like: View image As you can see, your Treasurers can obtain a holistic view of all cash positions across any number of bank accounts as well as other sources of cash flow movements. Depending on how they manage their accounts, they can also use this feature to initiate or monitor bank account sweeps or transfers between their zero balance accounts (ZBA) or cash pools. The cash position worksheet provide drill down for more detail and the ability to manually enter items directly into the worksheet for even greater flexibility and control. The enhancements to this feature were released last week. The following list the patches for Release 12.0.6 and 12.1.1: For more information, visit the following website. http://launch.oracle.com. PIN: yes2try

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  • Smart defaults [SSDT]

    - by jamiet
    I’ve just discovered a new, somewhat hidden, feature in SSDT that I didn’t know about and figured it would be worth highlighting here because I’ll bet not many others know it either; the feature is called Smart Defaults. It gets around the problem of adding a NOT NULLable column to an existing table that has got data in it – previous to SSDT you would need to define a DEFAULT constraint however it does feel rather cumbersome to create an object purely for the purpose of pushing through a deployment – that’s the situation that Smart Defaults is meant to alleviate. The Smart Defaults option exists in the advanced section of a Publish Profile file: The description of the setting is “Automatically provides a default value when updating a table that contains data with a column that does not allow null values”, in other words checking that option will cause SSDT to insert an arbitrary default value into your newly created NON NULLable column. In case you’re wondering how it does it, here’s how: SSDT creates a DEFAULT CONSTRAINT at the same time as the column is created and then immediately removes that constraint: ALTER TABLE [dbo].[T1]    ADD [C1] INT NOT NULL,         CONSTRAINT [SD_T1_1df7a5f76cf44bb593506d05ff9a1e2b] DEFAULT 0 FOR [C1];ALTER TABLE [dbo].[T1] DROP CONSTRAINT [SD_T1_1df7a5f76cf44bb593506d05ff9a1e2b]; You can then update the value as appropriate in a Post-Deployment script. Pretty cool! On the downside, you can only specify this option for the whole project, not for an individual table or even an individual column – I’m not sure that I’d want to turn this on for an entire project as it could hide problems that a failed deployment would highlight, in other words smart defaults could be seen to be “papering over the cracks”. If you think that should be improved go and vote (and leave a comment) at [SSDT] Allow us to specify Smart defaults per table or even per column. @Jamiet

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  • SQL Management Studio - Execute current line

    - by mawaldne
    In SQL Server 2008 Management studio, I can hit F5 to execute everything in the current query window. I can also highlight a query, and hit F5 to run that highlighted query. Instead of having to highlight a query, is there a way I can run the single query my cursor is on, or run a query my cursor is on up to a the first ';'?

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  • SQL Solstice

    - by andyleonard
    Introduction My friends in North Carolina have decided to create a new event called SQL Solstice . Details: 18 - 20 Aug 2011 Holiday Inn Brownstone & Conference Center 1707 Hillsborough Street - Raleigh, NC 27605 Toll Free 800-331-7919 18 Aug - A Day of Deep Dives ($259) Day-long presentations delivered by folks with real-world, hands-on experience. Louis Davidson on Database Design Andrew Kelly on Performance Tuning Jessica M. Moss on Reporting Services Ed Wilson on Powershell (me) on SSIS 19...(read more)

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  • SQL SERVER – Concurrancy Problems and their Relationship with Isolation Level

    - by pinaldave
    Concurrency is simply put capability of the machine to support two or more transactions working with the same data at the same time. This usually comes up with data is being modified, as during the retrieval of the data this is not the issue. Most of the concurrency problems can be avoided by SQL Locks. There are four types of concurrency problems visible in the normal programming. 1)      Lost Update – This problem occurs when there are two transactions involved and both are unaware of each other. The transaction which occurs later overwrites the transactions created by the earlier update. 2)      Dirty Reads – This problem occurs when a transactions selects data that isn’t committed by another transaction leading to read the data which may not exists when transactions are over. Example: Transaction 1 changes the row. Transaction 2 changes the row. Transaction 1 rolls back the changes. Transaction 2 has selected the row which does not exist. 3)      Nonrepeatable Reads – This problem occurs when two SELECT statements of the same data results in different values because another transactions has updated the data between the two SELECT statements. Example: Transaction 1 selects a row, which is later on updated by Transaction 2. When Transaction A later on selects the row it gets different value. 4)      Phantom Reads – This problem occurs when UPDATE/DELETE is happening on one set of data and INSERT/UPDATE is happening on the same set of data leading inconsistent data in earlier transaction when both the transactions are over. Example: Transaction 1 is deleting 10 rows which are marked as deleting rows, during the same time Transaction 2 inserts row marked as deleted. When Transaction 1 is done deleting rows, there will be still rows marked to be deleted. When two or more transactions are updating the data, concurrency is the biggest issue. I commonly see people toying around with isolation level or locking hints (e.g. NOLOCK) etc, which can very well compromise your data integrity leading to much larger issue in future. Here is the quick mapping of the isolation level with concurrency problems: Isolation Dirty Reads Lost Update Nonrepeatable Reads Phantom Reads Read Uncommitted Yes Yes Yes Yes Read Committed No Yes Yes Yes Repeatable Read No No No Yes Snapshot No No No No Serializable No No No No I hope this 400 word small article gives some quick understanding on concurrency issues and their relation to isolation level. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Introduction to Function SIGN

    - by pinaldave
    Yesterday I received an email from a friend asking how do SIGN function works. Well SIGN Function is very fundamental function. It will return the value 1, -1 or 0. If your value is negative it will return you negative -1 and if it is positive it will return you positive +1. Let us start with a simple small example. DECLARE @IntVal1 INT, @IntVal2 INT,@IntVal3 INT DECLARE @NumVal1 DECIMAL(4,2), @NumVal2 DECIMAL(4,2),@NumVal3 DECIMAL(4,2) SET @IntVal1 = 9; SET @IntVal2 = -9; SET @IntVal3 = 0; SET @NumVal1 = 9.0; SET @NumVal2 = -9.0; SET @NumVal3 = 0.0; SELECT SIGN(@IntVal1) IntVal1,SIGN(@IntVal2) IntVal2,SIGN(@IntVal3) IntVal3 SELECT SIGN(@NumVal1) NumVal1,SIGN(@NumVal2) NumVal2,SIGN(@NumVal2) NumVal3   The above function will give us following result set. You will notice that when there is positive value the function gives positive values and if the values are negative it will return you negative values. Also you will notice that if the data type is  INT the return value is INT and when the value passed to the function is Numeric the result also matches it. Not every datatype is compatible with this function.  Here is the quick look up of the return types. bigint -> bigint int/smallint/tinyint -> int money/smallmoney -> money numeric/decimal -> numeric/decimal everybody else -> float What will be the best example of the usage of this function that you will not have to use the CASE Statement. Here is example of CASE Statement usage and the same replaced with SIGN function. USE tempdb GO CREATE TABLE TestTable (Date1 SMALLDATETIME, Date2 SMALLDATETIME) INSERT INTO TestTable (Date1, Date2) SELECT '2012-06-22 16:15', '2012-06-20 16:15' UNION ALL SELECT '2012-06-24 16:15', '2012-06-22 16:15' UNION ALL SELECT '2012-06-22 16:15', '2012-06-22 16:15' GO -- Using Case Statement SELECT CASE WHEN DATEDIFF(d,Date1,Date2) > 0 THEN 1 WHEN DATEDIFF(d,Date1,Date2) < 0 THEN -1 ELSE 0 END AS Col FROM TestTable GO -- Using SIGN Function SELECT SIGN(DATEDIFF(d,Date1,Date2)) AS Col FROM TestTable GO DROP TABLE TestTable GO This was interesting blog post for me to write. Let me know your opinion. 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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