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  • Inequality joins, Asynchronous transformations and Lookups : SSIS

    - by jamiet
    It is pretty much accepted by SQL Server Integration Services (SSIS) developers that synchronous transformations are generally quicker than asynchronous transformations (for a description of synchronous and asynchronous transformations go read Asynchronous and synchronous data flow components). Notice I said “generally” and not “always”; there are circumstances where using asynchronous transformations can be beneficial and in this blog post I’ll demonstrate such a scenario, one that is pretty common when building data warehouses. Imagine I have a [Customer] dimension table that manages information about all of my customers as a slowly-changing dimension. If that is a type 2 slowly changing dimension then you will likely have multiple rows per customer in that table. Furthermore you might also have datetime fields that indicate the effective time period of each member record. Here is such a table that contains data for four dimension members {Terry, Max, Henry, Horace}: Notice that we have multiple records per customer and that the [SCDStartDate] of a record is equivalent to the [SCDEndDate] of the record that preceded it (if there was one). (Note that I am on record as saying I am not a fan of this technique of storing an [SCDEndDate] but for the purposes of clarity I have included it here.) Anyway, the idea here is that we will have some incoming data containing [CustomerName] & [EffectiveDate] and we need to use those values to lookup [Customer].[CustomerId]. The logic will be: Lookup a [CustomerId] WHERE [CustomerName]=[CustomerName] AND [SCDStartDate] <= [EffectiveDate] AND [EffectiveDate] <= [SCDEndDate] The conventional approach to this would be to use a full cached lookup but that isn’t an option here because we are using inequality conditions. The obvious next step then is to use a non-cached lookup which enables us to change the SQL statement to use inequality operators: Let’s take a look at the dataflow: Notice these are all synchronous components. This approach works just fine however it does have the limitation that it has to issue a SQL statement against your lookup set for every row thus we can expect the execution time of our dataflow to increase linearly in line with the number of rows in our dataflow; that’s not good. OK, that’s the obvious method. Let’s now look at a different way of achieving this using an asynchronous Merge Join transform coupled with a Conditional Split. I’ve shown it post-execution so that I can include the row counts which help to illustrate what is going on here: Notice that there are more rows output from our Merge Join component than on the input. That is because we are joining on [CustomerName] and, as we know, we have multiple records per [CustomerName] in our lookup set. Notice also that there are two asynchronous components in here (the Sort and the Merge Join). I have embedded a video below that compares the execution times for each of these two methods. The video is just over 8minutes long. View on Vimeo  For those that can’t be bothered watching the video I’ll tell you the results here. The dataflow that used the Lookup transform took 36 seconds whereas the dataflow that used the Merge Join took less than two seconds. An illustration in case it is needed: Pretty conclusive proof that in some scenarios it may be quicker to use an asynchronous component than a synchronous one. Your mileage may of course vary. The scenario outlined here is analogous to performance tuning procedural SQL that uses cursors. It is common to eliminate cursors by converting them to set-based operations and that is effectively what we have done here. Our non-cached lookup is performing a discrete operation for every single row of data, exactly like a cursor does. By eliminating this cursor-in-disguise we have dramatically sped up our dataflow. I hope all of that proves useful. You can download the package that I demonstrated in the video from my SkyDrive at http://cid-550f681dad532637.skydrive.live.com/self.aspx/Public/BlogShare/20100514/20100514%20Lookups%20and%20Merge%20Joins.zip Comments are welcome as always. @Jamiet Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Michael Stephenson joins CloudCasts

    - by Alan Smith
    Mike Stephenson has recorded a couple of webcasts focusing on build and test in BizTalk Server 2009. These are part of the “BizTalk Light & Easy” series of webcasts created by some of the BizTalk Server MVPs. Testing BizTalk Applications Implementing an Automated Build Process with BizTalk Server 2009

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  • Partition Wise Joins II

    - by jean-pierre.dijcks
    One of the things that I did not talk about in the initial partition wise join post was the effect it has on resource allocation on the database server. When Oracle applies a different join method - e.g. not PWJ - what you will see in SQL Monitor (in Enterprise Manager) or in an Explain Plan is a set of producers and a set of consumers. The producers scan the tables in the the join. If there are two tables the producers first scan one table, then the other. The producers thus provide data to the consumers, and when the consumers have the data from both scans they do the join and give the data to the query coordinator. Now that behavior means that if you choose a degree of parallelism of 4 to run such query with, Oracle will allocate 8 parallel processes. Of these 8 processes 4 are producers and 4 are consumers. The consumers only actually do work once the producers are fully done with scanning both sides of the join. In the plan above you can see that the producers access table SALES [line 11] and then do a PX SEND [line 9]. That is the producer set of processes working. The consumers receive that data [line 8] and twiddle their thumbs while the producers go on and scan CUSTOMERS. The producers send that data to the consumer indicated by PX SEND [line 5]. After receiving that data [line 4] the consumers do the actual join [line 3] and give the data to the QC [line 2]. BTW, the myth that you see twice the number of processes due to the setting PARALLEL_THREADS_PER_CPU=2 is obviously not true. The above is why you will see 2 times the processes of the DOP. In a PWJ plan the consumers are not present. Instead of producing rows and giving those to different processes, a PWJ only uses a single set of processes. Each process reads its piece of the join across the two tables and performs the join. The plan here is notably different from the initial plan. First of all the hash join is done right on top of both table scans [line 8]. This query is a little more complex than the previous so there is a bit of noise above that bit of info, but for this post, lets ignore that (sort stuff). The important piece here is that the PWJ plan typically will be faster and from a PX process number / resources typically cheaper. You may want to look out for those plans and try to get those to appear a lot... CREDITS: credits for the plans and some of the info on the plans go to Maria, as she actually produced these plans and is the expert on plans in general... You can see her talk about explaining the explain plan and other optimizer stuff over here: ODTUG in Washington DC, June 27 - July 1 On the Optimizer blog At OpenWorld in San Francisco, September 19 - 23 Happy joining and hope to see you all at ODTUG and OOW...

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  • Oracle Joins XBRL US To Help Drive Adoption

    - by Theresa Hickman
    Recently, Oracle joined XBRL US, the national consortium for XML business reporting standards to stay ahead of the technology and help increase XBRL adoption by U.S. companies by 2011. Large accelerated filers were mandated to use XBRL starting in 2009; other large filers started in 2010 and all other public companies must comply in June 2011. Here is a list of other organizations that recently joined XBRL US: Oracle Citi Federal Filings LLC Edgar Agents LLC XSP For those of you who have been living under a rock, XBRL stands for eXtensible Business Reporting Language. Simply put, it's reporting electronically. Just like PDFs or spreadsheets are a type of output, XBRL is another output option in electronic form. Right now, the transition to XBRL means extra work for publicly traded companies because they need to file their financial statements in both EDGAR and XBRL formats. Once the SEC phases out the EDGAR system, XBRL will be the primary way to deliver financial information with footnotes and supporting schedules to multiple audiences without having to re-key or reformat the information. A single XBRL document can be converted to printed output, published via the Web, fed into an SEC database (e.g. EDGAR) or forwarded to a creditor for analysis. Question: How does Oracle support XBRL reporting? Answer: The latest XBRL 2.1 specifications are supported by Oracle Hyperion Disclosure Management, which is part of Oracle's Hyperion Financial Close Suite along with Hyperion Financial Management, Hyperion Financial Data Quality Management and Hyperion Financial Close Management. Hyperion Disclosure Management supports the authoring of financial filings in Microsoft Office, with "hot links" to reports and data stored in Hyperion Financial Management or Oracle Essbase. It supports the XBRL tagging of financial statements as well as the disclosures and footnotes within your 10K and 10Q filings. Because many of our customers use Hyperion Financial Management (HFM) for their consolidation needs, they simply generate XBRL statements from their consolidated financial results. Question: What if you don't use Hyperion Financial Management, and you only use E-Business Suite General Ledger or PeopleSoft General Ledger? Answer: No problem, all you need is Hyperion Disclosure Management to generate XBRL from your general ledger. Here are the steps: Upload the XBRL taxonomy from the SEC or XBRL website into Hyperion Disclosure Management. Publish your financial statements out of general ledger to Excel. Perform the XBRL tag mapping from the Excel output to Hyperion Disclosure Management. For more information and some interesting background on XBRL, I recommend reading What You Need To Know About XBRL written by our EPM expert, John O'Rourke.

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  • Business School graduate joins Oracle

    - by jessica.ebbelaar(at)oracle.com
    My name is Mathias, I work as an Applications Inside Sales Rep for the French market, and I’d like to give you a brief snapshot of my experience at Oracle. First things first, how did you hear about Oracle? Where have you seen the sharp and recognizable red logo? Was it in Charles de Gaulle Airport when your eyes crossed the 20-metre banner with a picture of a strange big machine in the middle? Was it through reading the Forbes 10 top IT companies worldwide ranking? Or is it because IT is your thing and you cannot but know one of the “big four”? Meeting with a Grenoble Alumnus My story is a little different. My plan was to work in sales, in the IT industry. I had heard about Oracle, but my opinion at the time was that this kind of multinational company was way out of reach for a young graduate, even with high enthusiasm and great excitement to be (finally) on the job market. So, I was really surprised when I had an interesting conversation with a top alumnus of my business school. We were at the Grenoble Ecole de Management graduation ceremony (our graduation!), and before the party got really started, I got to chat with her. She told me of the great experience she was getting by living and working in Dublin. She had already figured it all out: “you work with another 100 young people from 10 different nationalities across Europe, you can be based in Dublin, but then once you work really hard you can move to Malaga Spain or other BUs around the world, you can work with different lines of business and learn about new “techy” and business oriented products, move to the field in your home country or elsewhere, etc.” What, what, what? Moving around Europe, trained by the best sales coaches in the world, acquiring strong IT knowledge and getting on board with one of fastest-growing and most watched companies in the world? Well, I was in. The next day (OK, 3 days after, the time to recover), I sent her my CV, and 3 months later I started as a Business Development Consultant at Oracle in Dublin, representing the latest cloud based CRM across the French market. That was 15 months ago. Since then, I moved line of business twice, I’m always learning new things and working with different and senior stakeholders; I have attended hundreds of hours of sales and product training (priceless when you come from a business background); I passed the Dublin Institute of Technology Sales Certification through different trainings given onsite within Oracle; I’ve led projects based around social media and I’ve gotten involved within various sales deals going on my market. Despite all of these great things, two will remain in my spirit: the multiculturalism that I experience every day in the office, and the American style of management - more direct and open than what you can find in “regular French companies”. Sales Progression Board In May 2012, I passed what we call a ‘Sales Progression Board’ to be promoted to an Inside Sales position. I am now in charge of generating revenue through the sale of Oracle applications on my specific territory. Always keeping in my mind my personal ambition: going to the field one day. Interested to join Oracle in the same role as Mathias? Visit http://campus.oracle.com.

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  • Microsoft joins the rest of us...and counts down to the end of IE6

    - by brian_ritchie
    Microsoft launched a website dedicated to the demise of IE6.  Here's their pitch...10 years ago a browser was born.  Its name was Internet Explorer 6. Now that we’re in 2011, in an era of modern web standards, it’s time to say goodbye. We'll watch Internet Explorer 6 usage drop to less than 1% worldwide, so more websites can choose to drop support for Internet Explorer 6, saving hours of work for web developers.  Thanks Microsoft!  We've been waiting for this day to come for a long time.  Of course, it would have been nice if IE6 was gone 5 years ago...but who's counting.

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  • Oracle Joins OpenDaylight Project, Plans to Integrate OpenDaylight SDN Capabilities Into Oracle Solaris

    - by CarylTakvorian-Oracle
    Good news for our Telco ISV partners who want to leverage virtualization technologies such as SDN and NFV: We just announced that Solaris 11.2 will integrate OpenDaylight SDN, and that Oracle will join the OpenDaylight project as a Silver member. The integration will allow customers to improve service quality and take advantage of apps-to-disk SLAs through compatibility with a wide range of SDN devices, applications and services. It will also allow them to use a common and open SDN platform with OpenStack to manage Oracle Solaris-based clouds. The OpenDaylight Project is a community-led and industry-supported open source platform to advance SDN and Network Functions Virtualization (NFV).

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  • Fun with Outer Joins

    Learn how an outer join works and how you can use it in your applications to find the results you need when matching data isn't in all your tables. Keep your database and application development in syncSQL Connect is a Visual Studio add-in that brings your databases into your solution. It then makes it easy to keep your database in sync, and commit to your existing source control system. Find out more.

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  • SQL SERVER – Merge Operations – Insert, Update, Delete in Single Execution

    - by pinaldave
    This blog post is written in response to T-SQL Tuesday hosted by Jorge Segarra (aka SQLChicken). I have been very active using these Merge operations in my development. However, I have found out from my consultancy work and friends that these amazing operations are not utilized by them most of the time. Here is my attempt to bring the necessity of using the Merge Operation to surface one more time. MERGE is a new feature that provides an efficient way to do multiple DML operations. In earlier versions of SQL Server, we had to write separate statements to INSERT, UPDATE, or DELETE data based on certain conditions; however, at present, by using the MERGE statement, we can include the logic of such data changes in one statement that even checks when the data is matched and then just update it, and similarly, when the data is unmatched, it is inserted. One of the most important advantages of MERGE statement is that the entire data are read and processed only once. In earlier versions, three different statements had to be written to process three different activities (INSERT, UPDATE or DELETE); however, by using MERGE statement, all the update activities can be done in one pass of database table. I have written about these Merge Operations earlier in my blog post over here SQL SERVER – 2008 – Introduction to Merge Statement – One Statement for INSERT, UPDATE, DELETE. I was asked by one of the readers that how do we know that this operator was doing everything in single pass and was not calling this Merge Operator multiple times. Let us run the same example which I have used earlier; I am listing the same here again for convenience. --Let’s create Student Details and StudentTotalMarks and inserted some records. USE tempdb GO CREATE TABLE StudentDetails ( StudentID INTEGER PRIMARY KEY, StudentName VARCHAR(15) ) GO INSERT INTO StudentDetails VALUES(1,'SMITH') INSERT INTO StudentDetails VALUES(2,'ALLEN') INSERT INTO StudentDetails VALUES(3,'JONES') INSERT INTO StudentDetails VALUES(4,'MARTIN') INSERT INTO StudentDetails VALUES(5,'JAMES') GO CREATE TABLE StudentTotalMarks ( StudentID INTEGER REFERENCES StudentDetails, StudentMarks INTEGER ) GO INSERT INTO StudentTotalMarks VALUES(1,230) INSERT INTO StudentTotalMarks VALUES(2,255) INSERT INTO StudentTotalMarks VALUES(3,200) GO -- Select from Table SELECT * FROM StudentDetails GO SELECT * FROM StudentTotalMarks GO -- Merge Statement MERGE StudentTotalMarks AS stm USING (SELECT StudentID,StudentName FROM StudentDetails) AS sd ON stm.StudentID = sd.StudentID WHEN MATCHED AND stm.StudentMarks > 250 THEN DELETE WHEN MATCHED THEN UPDATE SET stm.StudentMarks = stm.StudentMarks + 25 WHEN NOT MATCHED THEN INSERT(StudentID,StudentMarks) VALUES(sd.StudentID,25); GO -- Select from Table SELECT * FROM StudentDetails GO SELECT * FROM StudentTotalMarks GO -- Clean up DROP TABLE StudentDetails GO DROP TABLE StudentTotalMarks GO The Merge Join performs very well and the following result is obtained. Let us check the execution plan for the merge operator. You can click on following image to enlarge it. Let us evaluate the execution plan for the Table Merge Operator only. We can clearly see that the Number of Executions property suggests value 1. Which is quite clear that in a single PASS, the Merge Operation completes the operations of Insert, Update and Delete. I strongly suggest you all to use this operation, if possible, in your development. I have seen this operation implemented in many data warehousing applications. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Joins, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Merge

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  • rails multiple outer joins syntax

    - by Craig McGuff
    I have the following models user has_many :leave_balances leave_balance belongs_to :user belongs_to :leave_type leave_type has_many :leave_balances I want to output a table format showing user names and their balance by leave type. Not every user can have every balance i.e. outer joins required. I'd like to see something like this: Employee Annual Leave Sick Leave Bob 10 Fred 9 Sara 12 15 I am unsure how to get this out as a single statement? I am thinking something like User.joins(:leave_balances).joins(:leave_type)

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  • SQL SERVER – Example of Performance Tuning for Advanced Users with DB Optimizer

    - by Pinal Dave
    Performance tuning is such a subject that everyone wants to master it. In beginning everybody is at a novice level and spend lots of time learning how to master the art of performance tuning. However, as we progress further the tuning of the system keeps on getting very difficult. I have understood in my early career there should be no need of ego in the technology field. There are always better solutions and better ideas out there and we should not resist them. Instead of resisting the change and new wave I personally adopt it. Here is a similar example, as I personally progress to the master level of performance tuning, I face that it is getting harder to come up with optimal solutions. In such scenarios I rely on various tools to teach me how I can do things better. Once I learn about tools, I am often able to come up with better solutions when I face the similar situation next time. A few days ago I had received a query where the user wanted to tune it further to get the maximum out of the performance. I have re-written the similar query with the help of AdventureWorks sample database. SELECT * FROM HumanResources.Employee e INNER JOIN HumanResources.EmployeeDepartmentHistory edh ON e.BusinessEntityID = edh.BusinessEntityID INNER JOIN HumanResources.Shift s ON edh.ShiftID = s.ShiftID; User had similar query to above query was used in very critical report and wanted to get best out of the query. When I looked at the query – here were my initial thoughts Use only column in the select statements as much as you want in the application Let us look at the query pattern and data workload and find out the optimal index for it Before I give further solutions I was told by the user that they need all the columns from all the tables and creating index was not allowed in their system. He can only re-write queries or use hints to further tune this query. Now I was in the constraint box – I believe * was not a great idea but if they wanted all the columns, I believe we can’t do much besides using *. Additionally, if I cannot create a further index, I must come up with some creative way to write this query. I personally do not like to use hints in my application but there are cases when hints work out magically and gives optimal solutions. Finally, I decided to use Embarcadero’s DB Optimizer. It is a fantastic tool and very helpful when it is about performance tuning. I have previously explained how it works over here. First open DBOptimizer and open Tuning Job from File >> New >> Tuning Job. Once you open DBOptimizer Tuning Job follow the various steps indicates in the following diagram. Essentially we will take our original script and will paste that into Step 1: New SQL Text and right after that we will enable Step 2 for Generating Various cases, Step 3 for Detailed Analysis and Step 4 for Executing each generated case. Finally we will click on Analysis in Step 5 which will generate the report detailed analysis in the result pan. The detailed pan looks like. It generates various cases of T-SQL based on the original query. It applies various hints and available hints to the query and generate various execution plans of the query and displays them in the resultant. You can clearly notice that original query had a cost of 0.0841 and logical reads about 607 pages. Whereas various options which are just following it has different execution cost as well logical read. There are few cases where we have higher logical read and there are few cases where as we have very low logical read. If we pay attention the very next row to original query have Merge_Join_Query in description and have lowest execution cost value of 0.044 and have lowest Logical Reads of 29. This row contains the query which is the most optimal re-write of the original query. Let us double click over it. Here is the query: SELECT * FROM HumanResources.Employee e INNER JOIN HumanResources.EmployeeDepartmentHistory edh ON e.BusinessEntityID = edh.BusinessEntityID INNER JOIN HumanResources.Shift s ON edh.ShiftID = s.ShiftID OPTION (MERGE JOIN) If you notice above query have additional hint of Merge Join. With the help of this Merge Join query hint this query is now performing much better than before. The entire process takes less than 60 seconds. Please note that it the join hint Merge Join was optimal for this query but it is not necessary that the same hint will be helpful in all the queries. Additionally, if the workload or data pattern changes the query hint of merge join may be no more optimal join. In that case, we will have to redo the entire exercise once again. This is the reason I do not like to use hints in my queries and I discourage all of my users to use the same. However, if you look at this example, this is a great case where hints are optimizing the performance of the query. It is humanly not possible to test out various query hints and index options with the query to figure out which is the most optimal solution. Sometimes, we need to depend on the efficiency tools like DB Optimizer to guide us the way and select the best option from the suggestion provided. Let me know what you think of this article as well your experience with DB Optimizer. Please leave a comment. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Joins, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Not Possible – Delete From Multiple Table – Update Multiple Table in Single Statement

    - by pinaldave
    There are two questions which I get every single day multiple times. In my gmail, I have created standard canned reply for them. Let us see the questions here. I want to delete from multiple table in a single statement how will I do it? I want to update multiple table in a single statement how will I do it? The answer is – No, You cannot and you should not. SQL Server does not support deleting or updating from two tables in a single update. If you want to delete or update two different tables – you may want to write two different delete or update statements for it. This method has many issues – from the consistency of the data to SQL syntax. Now here is the real reason for this blog post – yesterday I was asked this question again and I replied my canned answer saying it is not possible and it should not be any way implemented that day. In the response to my reply I was pointed out to my own blog post where user suggested that I had previously mentioned this is possible and with demo example. Let us go over my conversation – you may find it interesting. Let us call the user DJ. DJ: Pinal, can we delete multiple table in a single statement or with single delete statement? Pinal: No, you cannot and you should not. DJ: Oh okey, if that is the case, why do you suggest to do that? Pinal: (baffled) I am not suggesting that. I am rather suggesting that it is not possible and it should not be possible. DJ: Hmm… but in that case why did you blog about it earlier? Pinal: (What?) No, I did not. I am pretty confident. DJ: Well, I am confident as well. You did. Pinal: In that case, it is my word against your word. Isn’t it? DJ: I have proof. Do you want to see it that you suggest it is possible? Pinal: Yes, I will be delighted too. (After 10 Minutes) DJ: Here are not one but two of your blog posts which talks about it - SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2 SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – T-SQL Example – Part 2 of 2 Pinal: Oh! DJ: I know I was correct. Pinal: Well, oh man, I did not mean there what you mean here. DJ: I did not understand can you explain it further. Pinal: Here we go. The example in the other blog is the example of the cascading delete or cascading update. I think you may want to understand the concept of the foreign keys and cascading update/delete. The concept of cascading exists to maintain data integrity. If there primary keys get deleted the update or delete reflects on the foreign key table to maintain the key integrity and data consistency. SQL Server follows ANSI Entry SQL with regard to referential integrity between PrimaryKey and ForeignKey columns which requires the inserting, updating, and deleting of data in related tables to be restricted to values that preserve the integrity. This is all together different concept than deleting multiple values in a single statement. When I hear that someone wants to delete or update multiple table in a single statement what I assume is something very similar to following. DELETE/UPDATE Table 1 (cols) Table 2 (cols) VALUES … which is not valid statement/syntax as well it is not ASNI standards as well. I guess, after this discussion with DJ, I realize I need to do a blog post so I can add the link to this blog post in my canned answer. Well, it was a fun conversation with DJ and I hope it the message is very clear now. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Joins, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • LINQ Joins - Performance

    - by Meiscooldude
    I am curious on how exactly LINQ (not LINQ to SQL) is performing is joins behind the scenes in relation to how Sql Server performs joins. Sql Server before executing a query, generates an Execution Plan. The Execution Plan is basically an Expression Tree on what it believes is the best way to execute the query. Each node provides information on whether to do a Sort, Scan, Select, Join, ect. On a 'Join' node in our execution plan, we can see three possible algorithms; Hash Join, Merge Join, and Nested Loops Join. Sql Server will choose which algorithm to for each Join operation based on expected number of rows in Inner and Outer tables, what type of join we are doing (some algorithms don't support all types of joins), whether we need data ordered, and probably many other factors. Join Algorithms: Nested Loop Join: Best for small inputs, can be optimized with ordered inner table. Merge Join: Best for medium to large inputs sorted inputs, or an output that needs to be ordered. Hash Join: Best for medium to large inputs, can be parallelized to scale linearly. LINQ Query: DataTable firstTable, secondTable; ... var rows = from firstRow in firstTable.AsEnumerable () join secondRow in secondTable.AsEnumerable () on firstRow.Field<object> (randomObject.Property) equals secondRow.Field<object> (randomObject.Property) select new {firstRow, secondRow}; SQL Query: SELECT * FROM firstTable fT INNER JOIN secondTable sT ON fT.Property = sT.Property Sql Server might use a Nested Loop Join if it knows there are a small number of rows from each table, a merge join if it knows one of the tables has an index, and Hash join if it knows there are a lot of rows on either table and neither has an index. Does Linq choose its algorithm for joins? or does it always use one?

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  • Performance on joins in linq

    - by swapna
    HI , I am going to rewrite a store procedure in LINQ. What this sp is doing is joining 12 tables and get the data and insert it into another table. it has 7 left outer joins and 4 inner joins.And returns one row of data. Now question. 1)What is the best way to achieve this joins in linq. 2) do you think this affect performance (its only retrieving one row of data at a given point of time) Please advice. Thanks SNA.

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  • Hibernate HQL to basic SQL (no joins)

    - by CC
    Hello everybody, I working on a project with Hibernate and we need to replace Hibernate with some "home made persistence" stuff. The idea is that the project is big enough, and we have many HQL queries. The problem is with the queries like select a,b from table1, table2 on t1.table1=t2.table2 Basically all joins are not supported by our "hand made persistence" stuff. What I would need, is to be able to do some sort of transcoder, which will take as a input the HQL queries and output some SQL, but SQL without joins I hope you get the idea. My persistence layer does not supports joins. Does anybody has any idea about something like that? Some framework, or something? Thanks alot everybody. C.C.

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  • app engine jpa N-way joins ?

    - by cometta
    may i know is the latest version of jgae support N-way joins? or still limit to 2-way join? reference: http://gae-java-persistence.blogspot.com/2010/03/executing-simple-joins-across-owned.html?showComment=1276491851890_AIe9_BEqp-CCn0bibiOUY8JUbbSFwFE02aF9d68baX0squIcfBnve8K3iIT3IEhPhpJxEBSZQLlz8tH-NMq1XGzOV0fAA8othN4f3zhR2B6xN0WzsTRpyEZJl2vPDonhVY38iUhJGe8Ot9URs3IjYk4HoH9LG41az7l0blTBNNnpJuyI-xl5CDJGoPLGk5jw4tLvtvsCYhq3n7XuiZwJIaBMWjHSDdy7-fB1NYszI0G4f9JRjZ5UdDM4at3o3tAhd-CYK2Af1dnG#c3679507832415682306

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  • Why are joins bad when considering scalability?

    - by acidzombie24
    Why are joins bad or 'slow'. I know i heard this more then once. I found this quote The problem is joins are relatively slow, especially over very large data sets, and if they are slow your website is slow. It takes a long time to get all those separate bits of information off disk and put them all together again. source I always thought they were fast especially when looking up a PK. Why are they 'slow'?

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  • Discover intended Foreign Keys from JOINS in scripts

    - by Jason
    I'm inheriting a database that has 400 tables and only 150 foreign key constraints registered. Knowing what I do about the application and looking at the table columns, it's easy to say that there ought to be a lot more. I'm afraid that the current application software will break if I started adding the missing FKs because the developers have probably come to rely on this "freedom", but step one in fixing the problem is to come up with the list of missing FKs so we can evaluate them as a team. To make matters worse, the referencing columns don't share a naming convention. The relationships ARE coded informally into the hundreds of ad-hoc queries and stored procedures, so my hope is to parse these files programmatically looking for JOINS between actual tables (but not table variables, etc). Challenges I foresee in this approach are: newlines, optional aliases and table hints, alias resolution. Any better ideas? (Besides quitting) Are there any pre-built tools that can solve this? I don't think regex can handle this. Do you disagree? SQL Parsers? I tried using Microsoft.SqlServer.Management.SqlParser.Parser but all that is exposed is the lexer - can't get an AST out of it - all that stuff is internal.

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  • using joins or multiple queries in php/mysql

    - by askkirati
    Here i need help with joins. I have two tables say articles and users. while displaying articles i need to display also the user info like username, etc. So will it be better if i just use joins to join the articles and user tables to fetch the user info while displaying articles like below. SELECT a.*,u.username,u.id FROM articles a JOIN users u ON u.id=a.user_id OR can this one in php. First i get the articles with below sql SELECT * FROM articles Then after i get the articles array i loop though it and get the user info inside each loop like below SELECT username, id FROM users WHERE id='".$articles->user_id."'; Which is better can i have explanation on why too. Thank you for any reply or views

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