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• How can I test database access methods in Java?

  - by javaStudent

  I want to write a test for a method that accesses a database such as following. public class MyClass{ public String getAddress(Int id){ String query = "Select * from Address where id="+id; //some additional statements resultSet = statement.executeQuery(); return result.getString(ADDRESS); } } How can I test this method? I am using Java.

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• What is a good strategy for binding view objects to model objects in C++?

  - by B.J.

  Imagine I have a rich data model that is represented by a hierarchy of objects. I also have a view hierarchy with views that can extract required data from model objects and display the data (and allow the user to manipulate the data). Actually, there could be multiple view hierarchies that can represent and manipulate the model (e.g. an overview-detail view and a direct manipulation view). My current approach for this is for the controller layer to store a reference to the underlying model object in the View object. The view object can then get the current data from the model for display, and can send the model object messages to update the data. View objects are effectively observers of the model objects and the model objects broadcast notifications when properties change. This approach allows all the views to update simultaneously when any view changes the model. Implemented carefully, this all works. However, it does require a lot of work to ensure that no view or model objects hold any stale references to model objects. The user can delete model objects or sub-hierarchies of the model at any time. Ensuring that all the view objects that hold references to the model objects that have been deleted is time-consuming and difficult. It feels like the approach I have been taking is not especially clean; while I don't want to have to have explicit code in the controller layer for mediating the communication between the views and the model, it seems like there must be a better (implicit) approach for establishing bindings between the view and the model and between related model objects. In particular, I am looking for an approach (in C++) that understands two key points: There is a many to one relationship between view and model objects If the underlying model object is destroyed, all the dependent view objects must be cleaned up so that no stale references exist While shared_ptr and weak_ptr can be used to manage the lifetimes of the underlying model objects and allows for weak references from the view to the model, they don't provide for notification of the destruction of the underlying object (they do in the sense that the use of a stale weak_ptr allows for notification), but I need an approach that notifies the dependent objects that their weak reference is going away. Can anyone suggest a good strategy to manage this?

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• OpenGL ES 2 jittery camera movement

  - by user16547

  First of all, I am aware that there's no camera in OpenGL (ES 2), but from my understanding proper manipulation of the projection matrix can simulate the concept of a camera. What I'm trying to do is make my camera follow my character. My game is 2D, btw. I think the principle is the following (take Super Mario Bros or Doodle Jump as reference - actually I'm trying to replicate the mechanics of the latter): when the caracter goes beyond the center of the screen (in the positive axis/direction), update the camera to be centred on the character. Else keep the camera still. I did accomplish that, however the camera movement is noticeably jittery and I ran out of ideas how to make it smoother. First of all, my game loop (following this article): private int TICKS_PER_SECOND = 30; private int SKIP_TICKS = 1000 / TICKS_PER_SECOND; private int MAX_FRAMESKIP = 5; @Override public void run() { loops = 0; if(firstLoop) { nextGameTick = SystemClock.elapsedRealtime(); firstLoop = false; } while(SystemClock.elapsedRealtime() > nextGameTick && loops < MAX_FRAMESKIP) { step(); nextGameTick += SKIP_TICKS; loops++; } interpolation = ( SystemClock.elapsedRealtime() + SKIP_TICKS - nextGameTick ) / (float)SKIP_TICKS; draw(); } And the following code deals with moving the camera. I was unsure whether to place it in step() or draw(), but it doesn't make a difference to my problem at the moment, as I tried both and neither seemed to fix it. center just represents the y coordinate of the centre of the screen at any time. Initially it is 0. The camera object is my own custom "camera" which basically is a class that just manipulates the view and projection matrices. if(character.getVerticalSpeed() >= 0) { //only update camera if going up float[] projectionMatrix = camera.getProjectionMatrix(); if( character.getY() > center) { center += character.getVerticalSpeed(); cameraBottom = center + camera.getBottom(); cameraTop = center + camera.getTop(); Matrix.orthoM(projectionMatrix, 0, camera.getLeft(), camera.getRight(), center + camera.getBottom(), center + camera.getTop(), camera.getNear(), camera.getFar()); } } Any thought about what I should try or what I am doing wrong? Update 1: I think I updated every value you can see on screen to check whether the jittery movement is affected by that, but nothing changed, so something must be fundamentally flawed with my approach/calculations.

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• Google Maps API Round-up

  Google Maps API Round-up This week, Mano Marks and Paul Saxman go over recent launches and things you might have missed with the Google Maps APIs, including the new Google Time Zone API, traffic estimates with the Directions API (for enterprise customers), and the Places Autocomplete API query results and data service enhancements. From: GoogleDevelopers Views: 0 0 ratings Time: 00:00 More in Education

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• Oracle Advanced Compression Webcast Replay Available

  - by [email protected]

  Did you miss our webcast "Save BIG on Storage - with Oracle Database 11g and Advanced Compression"? Don't worry, you can still register and view the recording including the full Q&A session with Tim Shetler and Bill Hodak. Click here to learn how Oracle Advanced Compression can reduce your disk space requirements for all types of data, improve query and storage performance and lower storage costs throughout the datacenter.

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• Applying Advanced Search Operators

  Search engines have developed additional applications termed advanced search operators to offer power internet marketers even more control each time searching. Advanced search operators are exclusive terms which you could place as part of your search query in order to come across unique sorts of details which a common search can not offer. A number of of those operators provide valuable tools for SEO specialists as well as other people who desire rather specific details, or maybe who need to restrict their particular search to extremely distinct source.

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• PeopleSoft Grants & the Federal Agency Letter of Credit Draw Changes

  - by Mark Rosenberg

  For decades, most, if not all, US Federal agencies that sponsor research allowed grant recipients to request and receive payments using pooled accounts, commonly known as pooled letter of credit (LOC) draws. This enabled organizations, such as universities and hospitals, fast and efficient access to reimbursement of the expenditures they incurred conducting research across a portfolio of grants. To support this business practice, the PeopleSoft Grants solution has delivered an LOC Draw report to provide the total request amount along with all of the supporting invoice details for reconciliation and audit purposes. Now, in an attempt to provide greater transparency, eliminate fraud, strengthen accountability for grant-related financial transactions, and simplify grant award closeout, many US Federal sponsors are transitioning from the “pooling” letter of credit draw method to requesting on a “grant-by-grant” basis. The National Science Foundation, the second largest issuer of Federal awards, already transitioned to detailed grant draws in 2013. And, in response to the U.S. Department of Health and Human Services (HHS) directive to HHS-supported Agencies, the largest Federal awards sponsor, the National Institutes of Health (NIH), will fully transition to the new HHS subaccount draw method. This will require NIH award recipients to request payments based on actual expenses incurred on an award-by-award basis. NIH is expected to fully transition to this new draw method by the end of Federal fiscal year 2015.  (The NIH had planned to fully transition to this new method by the end of fiscal 2014; however, the impact to institutions was deemed to be significant enough that a reprieve was recently granted.) In light of these new Federal draw requirements, we have recently released these new features to aid our customers on both PeopleSoft Grants releases 9.1 and 9.2:1. Federal Award Identification Number on the Proposal and Award Profile 2. Letter of credit fields on contract lines to support award basis draws and comply with Federal close out mandates3. Process to produce both pro forma and final LOC Draw Reports in BI Publisher report format4. Subacccount ID field on the LOC Summary and a new BI Publisher version of the LOC Summary report 5. Added Subaccount Field and contract info to be displayed on the LOC summary page6. Ability to generate by a variety of dimensions pro forma and invoiced draw listings 7. Queries for generation and manipulation of data to upload into sponsor payment request systems and perform payment matching8. Contracts LOC Close Out query to quickly review final balances prior to initiating final draws and preparing Federal Financial Reports prior to close The PeopleSoft Development team actively monitors this and other major Federal changes and continues working closely with the Grants Product Advisory Group of the Higher Education User Group to ensure a clear understanding of what our customers need in order to transition to new approaches for doing business with the Federal government. For more information regarding the enhancements to the PeopleSoft Grants solution, existing customers can login to My Oracle Support and review the Enhancements to Letter of Credit Process (Doc ID 1912692.1) associated with resolution ID 904830. This enhanced LOC functionality is available in both PeopleSoft FSCM 9.1 Bundle #31 and PeopleSoft FSCM 9.2 Update Image 8.

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• T-SQL bits - ROW_NUMBER

  - by MartinIsti

  About a month ago I found the SQLShare site which provides useful, clear tutorial videos of how to use some SQL functions, or how to fine tune a query. Their videos are roughly 3-5 minutes long and have proved to be very good for me with a strong BI background with less first-hand T-SQL experience. I decided to make notes of the ones I watched and found useful and instead of putting them into a word document somewhere locally I'll publish them on this blog so. These would be very simple and short...(read more)

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• SQL Injection prevention

  - by simonsabin

  Just asking people not to use a list of certain words is not prevention from SQL Injection https://homebank.sactocu.org/UA2004/faq-mfa.htm#pp6 To protect yourself from SQL Injection you have to do 1 simple thing. Do not build your SQL statements by concatenating values passed by the user into a string an executing them. If your query has to be dynamic then make sure any values passed by a user are passed as parameters and use sp_executesql in TSQL or a SqlCommand object in ADO.Net...(read more)

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• TSQL Challenge 47 - Read the modification history and identify the fir

  A table contains the list of modifications made to each card. Your job is to write a query that shows the first number, current number (most recent) and the number of changes made. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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• Celko's SQL Stumper: Eggs in one Basket

  Joe Celko returns with another stumper to celebrate Easter. Unsurprisingly, this involves eggs. More surprising is the nature of the puzzle: This time, the puzzle is one of designing a database rather than a query. DDL as well as the DML.

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• SQL SERVER Find Most Expensive Queries Using DMV

  The title of this post is what I can express here for this quick blog post. I was asked in recent query tuning consultation project, if I can share my script which I use to figure out which is the most expensive queries are running on SQL Server. This script is very basic and very [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• What causes Multi-Page allocations?

  - by SQLOS Team

  Writing about changes in the Denali Memory Manager In his last post Rusi mentioned: " In previous SQL versions only the 8k allocations were limited by the ‘max server memory’ configuration option.  Allocations larger than 8k weren’t constrained." In SQL Server versions before Denali single page allocations and multi-Page allocations are handled by different components, the Single Page Allocator (which is responsible for Buffer Pool allocations and governed by 'max server memory') and the Multi-Page allocator (MPA) which handles allocations of greater than an 8K page. If there are many multi-page allocations this can affect how much memory needs to be reserved outside 'max server memory' which may in turn involve setting the -g memory_to_reserve startup parameter. We'll follow up with more generic articles on the new Memory Manager structure, but in this post I want to clarify what might cause these larger allocations. So what kinds of query result in MPA activity? I was asked this question the other day after delivering an MCM webcast on Memory Manager changes in Denali. After asking around our Dev team I was connected to one of our test leads Sangeetha who had tested the plan cache, and kindly provided this example of an MPA intensive query: A workload that has stored procedures with a large # of parameters (say > 100, > 500), and then invoked via large ad hoc batches, where each SP has different parameters will result in a plan being cached for this “exec proc” batch. This plan will result in MPA.   Exec proc_name @p1, ….@p500 Exec proc_name @p1, ….@p500 . . . Exec proc_name @p1, ….@p500 Go   Another workload would be large adhoc batches of the form: Select * from t where col1 in (1, 2, 3, ….500) Select * from t where col1 in (1, 2, 3, ….500) Select * from t where col1 in (1, 2, 3, ….500) … Go  In Denali all page allocations are handled by an "Any size page allocator" and included in 'max server memory'. The buffer pool effectively becomes a client of the any size page allocator, which in turn relies on the memory manager. - Guy Originally posted at http://blogs.msdn.com/b/sqlosteam/

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• SSIS - Range lookups

  - by Repieter

    When developing an ETL solution in SSIS we sometimes need to do range lookups in SSIS. Several solutions for this can be found on the internet, but now we have built another solution which I would like to share, since it's pretty easy to implement and the performance is fast.   You can download the sample package to see how it works. Make sure you have the AdventureWorks2008R2 and AdventureWorksDW2008R2 databases installed. (Apologies for the layout of this blog, I don't do this too often :))   To give a little bit more information about the example, this is basically what is does: we load a facttable and do an SCD type 2 lookup operation of the Product dimension. This is done with a script component.   First we query the Data warehouse to create the lookup dataset. The query that is used for that is:   SELECT     [ProductKey]     ,[ProductAlternateKey]     ,[StartDate]     ,ISNULL([EndDate], '9999-01-01') AS EndDate FROM [DimProduct]     The output of this query is stored in a DataTable:     string lookupQuery = @"                         SELECT                             [ProductKey]                             ,[ProductAlternateKey]                             ,[StartDate]                             ,ISNULL([EndDate], '9999-01-01') AS EndDate                         FROM [DimProduct]";           OleDbCommand oleDbCommand = new OleDbCommand(lookupQuery, _oleDbConnection);         OleDbDataAdapter adapter = new OleDbDataAdapter(oleDbCommand);           _dataTable = new DataTable();         adapter.Fill(_dataTable);     Now that the dimension data is stored in the DataTable we use the following method to do the actual lookup:   public int RangeLookup(string businessKey, DateTime lookupDate)     {         // set default return value (Unknown)         int result = -1;           DataRow[] filteredRows;         filteredRows = _dataTable.Select(string.Format("ProductAlternateKey = '{0}'", businessKey));           for (int i = 0; i < filteredRows.Length; i++)         {             // check if the lookupdate is found between the startdate and enddate of any of the records             if (lookupDate >= (DateTime)filteredRows[i][2] && lookupDate < (DateTime)filteredRows[i][3])             {                 result = (filteredRows[i][0] == null) ? -1 : (int)filteredRows[i][0];                 break;             }         }           filteredRows = null;           return result;     }       This method is executed for every row that passes the script component. This is implemented in the ProcessInputRow method   public override void Input0_ProcessInputRow(Input0Buffer Row)     {         // Perform the lookup operation on the current row and put the value in the Surrogate Key Attribute         Row.ProductKey = RangeLookup(Row.ProductNumber, Row.OrderDate);     }   Now what actually happens?!   1. Every record passes the business key and the orderdate to the RangeLookup method. 2. The DataTable is then filtered on the business key of the current record. The output is stored in a DataRow [] object. 3. We loop over the DataRow[] object to see where the orderdate meets the following expression: (lookupDate >= (DateTime)filteredRows[i][2] && lookupDate < (DateTime)filteredRows[i][3]) 4. When the expression returns true (so where the data is between the Startdate and the EndDate), the surrogate key of the dimension record is returned   We have done some testing with this solution and it works great for us. Hope others can use this example to do their range lookups.

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• What shall I include in a 10 week web technologies course?

  - by Iain

  In September I will be teaching a university module on web technologies. This session will be available to 1st year (freshman) students who don't necessarily have any programming knowledge or know how the web works. In the 2nd semester I will be teaching Flash, which is my specialism, so I know exactly what I am going to teach, but in the 1st semester I will be teaching them web standards technologies - HTML, CSS, JS, jQuery, PHP and MySQL. Where I need advice is how to proportion the emphasis for each part, and which parts of each technology to cover. Another real issue I'm struggling with is how much of the bad old ways should I teach them? Do they need to know about bold as well as strong, etc. UPDATE: based, on your feedback I will only be teaching the latest version of everything - CSS3, HTML5 etc. I'm not sure exactly how long the semester will be but I'm guessing about 10-12 weeks. Each session is a 2 hour lab. Obviously there's only so much I can cover in that time and it will be up to the students to go a research this stuff properly on W3 schools etc. My ideas so far were: Lesson 0 - Course intro and overview of the current tech landscape. What is out there, what will we be learning, what won't we. What is a web server, URL etc. Looking at different example websites and discussing how they work. Lesson 1 - HTML basics (head, body, title, img, table, a, lists, h1, strong etc) Lesson 2 - CSS for styling and layout - fonts, webfonts, float etc Lesson 3 - Intro to programming JS (variables, loops, conditionals, functions) Lesson 4 - more JS programming fundamentals, DOM manipulation Lesson 5 - jQuery - making things fly about and look cool Lesson 6 - XML and Ajax Lesson 7 - PHP basics - syntax, server-side principles Lesson 8 - PHP and MySQL - forms, logins, saving user info Lesson 9 - don't know Lesson 10 - don't know Please let me know if you think this is the right order, what have I missed, how to use any spare sessions etc. Thanks :) UPDATE BASED ON RESPONSES: Thanks for all your responses - some great stuff. To be absolutely clear, this is not a computer science course, it is a practical module on a creative technology course. The emphasis definitely has to be on making cool things work rather than understanding how the backbone of the internet works. That can come later, if the students are interested. At the end of the module I would like the students to be able to produce a web page or pages that does something cool, using some or all of the technologies I cover. Many of these topics are of course far beyond the scope of a 2 hour session, however I do not have the option of reducing the syllabus, I will just have to explain what the technology does and encourage the student to research it in their own time.

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• Understanding exceptional cases

  - by Justin

  I've been studying the use of exceptions in various php projects (such as Doctrine and Zend Framework). Exceptions seem to be thrown when unordinary input/state occurs. A perfect example is Doctrine throwing an exception when you try to use a invalid query string. I think the creators of the doctrine api understood that first, you can't query data by using an invalid DQL statement, and a developer should immediately be warned that an error has occurred, rather then letting execution continue with the possibility of an error code going un-checked. I also bet that this simplifies reading the code. I can't think of a situation where you would want to use an invalid DQL statement, except unit testing. Since this is true, it's better to avoid plaguing a bunch of code with null/error checks and use exceptions. I've read in books that exceptions shouldn't be thrown when validating dating user input. I've seen examples where of where the guideline is broken. One example is the Zend framework. If supplying an invalid controller or action name, an exception is thrown. Unlike doctrine, the user has more direct control over this sort of input. I know you can configure an error controller and set up a 404 message or what have you, but I'm curious why they have used an exception in this scenario? I guess you can argue the Zend Framework does not know how to continue processing the quest. One last example Is I wrote a function to return some html based on a given resource type. This resource type is hard-coded and sent when a user interacts with a web site (such as clicking a button to display the form to input data). I don't expect users to be mucking around with the request type. Under normal operating conditions, the resource type should be valid. To clean up some logic, I was going to throw an exception if a particular form wasn't found. This is mainly to find the correct form associated with a resource type so proper validation can occur. Does this sound like a valid use case for an exception? Right now it's pretty trivial, but I do plan to implement a restful consumer and re-using a function to map resources to their validation services would be very useful. I can then catch the exception and based on the consumer, return an error message suitable for the request type...

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• How to make sure you see the truth with Management Studio

  - by fatherjack

  LiveJournal Tags: TSQL,How To,SSMS,Tips and Tricks Did you know that SQL Server Management Studio can mislead you with how your code is performing? I found a query that was using a scalar function to return a date and wanted to take the opportunity to remove it in favour of a table valued function that would be more efficient. The original function was simply returning the start date of the current financial year. The code we were using was: ALTER  FUNCTION...(read more)

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• Additional Columns in StreamInsight Event Flow Debugger

  This tool is excellent when investigating what is going on in your StreamInsight Streams.  I was looking through the menu items recently and went to Query => Event Fields I found that there were a couple of columns not added by default to the event viewer (Reminds me of the fact that the Variables viewer in SSIS hides columns also) Latency NewEndTime EnqueueTime Here they all are together.     This gives us even more information about what is going on

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• How are Reads Distributed in a Workload

  - by Bill Graziano

  People have uploaded nearly one millions rows of trace data to TraceTune.  That’s enough data to start to look at the results in aggregate.  The first thing I want to look at is logical reads.  This is the easiest metric to identify and fix. When you upload a trace, I rank each statement based on the total number of logical reads.  I also calculate each statement’s percentage of the total logical reads.  I do the same thing for CPU, duration and logical writes.  When you view a statement you can see all the details like this: This single statement consumed 61.4% of the total logical reads on the system while we were tracing it.  I also wanted to see the distribution of reads across statements.  That graph looks like this: On average, the highest ranked statement consumed just under 50% of the reads on the system.  When I tune a system, I’m usually starting in one of two modes: this “piece” is slow or the whole system is slow.  If a given piece (screen, report, query, etc.) is slow you can usually find the specific statements behind it and tune it.  You can make that individual piece faster but you may not affect the whole system. When you’re trying to speed up an entire server you need to identity those queries that are using the most disk resources in aggregate.  Fixing those will make them faster and it will leave more disk throughput for the rest of the queries. Here are some of the things I’ve learned querying this data: The highest ranked query averages just under 50% of the total reads on the system. The top 3 ranked queries average 73% of the total reads on the system. The top 10 ranked queries average 91% of the total reads on the system. Remember these are averages across all the traces that have been uploaded.  And I’m guessing that people mainly upload traces where there are performance problems so your mileage may vary. I also learned that slow queries aren’t the problem.  Before I wrote ClearTrace I used to identify queries by filtering on high logical reads using Profiler.  That picked out individual queries but those rarely ran often enough to put a large load on the system. If you look at the execution count by rank you’d see that the highest ranked queries also have the highest execution counts.  The graph would look very similar to the one above but flatter.  These queries don’t look that bad individually but run so often that they hog the disk capacity. The take away from all this is that you really should be tuning the top 10 queries if you want to make your system faster.  Tuning individually slow queries will help those specific queries but won’t have much impact on the system as a whole.

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• What does the impression and ctr means in google webmaster

  - by KoolKabin

  I am checking google webmaster tools. I entered the search queries section. There i found alot keywords and their impression and ctr etc. I clicked on one of the query keyword there it shows the keyword and position in search result, but when i go to google.com and type the specified keyword it shows no impressions too... how do i measure find my site's impression on google.com my site: http://www.trekkingandtoursnepal.com keyword: trekking nepal

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• How granular should a command be in a CQ[R]S model?

  - by Aaronaught

  I'm considering a project to migrate part of our WCF-based SOA over to a service bus model (probably nServiceBus) and using some basic pub-sub to achieve Command-Query Separation. I'm not new to SOA, or even to service bus models, but I confess that until recently my concept of "separation" was limited to run-of-the-mill database mirroring and replication. Still, I'm attracted to the idea because it seems to provide all the benefits of an eventually-consistent system while sidestepping many of the obvious drawbacks (most notably the lack of proper transactional support). I've read a lot on the subject from Udi Dahan who is basically the guru on ESB architectures (at least in the Microsoft world), but one thing he says really puzzles me: As we get larger entities with more fields on them, we also get more actors working with those same entities, and the higher the likelihood that something will touch some attribute of them at any given time, increasing the number of concurrency conflicts. [...] A core element of CQRS is rethinking the design of the user interface to enable us to capture our users’ intent such that making a customer preferred is a different unit of work for the user than indicating that the customer has moved or that they’ve gotten married. Using an Excel-like UI for data changes doesn’t capture intent, as we saw above. -- Udi Dahan, Clarified CQRS From the perspective described in the quotation, it's hard to argue with that logic. But it seems to go against the grain with respect to SOAs. An SOA (and really services in general) are supposed to deal with coarse-grained messages so as to minimize network chatter - among many other benefits. I realize that network chatter is less of an issue when you've got highly-distributed systems with good message queuing and none of the baggage of RPC, but it doesn't seem wise to dismiss the issue entirely. Udi almost seems to be saying that every attribute change (i.e. field update) ought to be its own command, which is hard to imagine in the context of one user potentially updating hundreds or thousands of combined entities and attributes as it often is with a traditional web service. One batch update in SQL Server may take a fraction of a second given a good highly-parameterized query, table-valued parameter or bulk insert to a staging table; processing all of these updates one at a time is slow, slow, slow, and OLTP database hardware is the most expensive of all to scale up/out. Is there some way to reconcile these competing concerns? Am I thinking about it the wrong way? Does this problem have a well-known solution in the CQS/ESB world? If not, then how does one decide what the "right level" of granularity in a Command should be? Is there some "standard" one can use as a starting point - sort of like 3NF in databases - and only deviate when careful profiling suggests a potentially significant performance benefit? Or is this possibly one of those things that, despite several strong opinions being expressed by various experts, is really just a matter of opinion?

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• Stairway to SQLCLR Level 3: Security (General and SAFE Assemblies)

  In the third level of our Stairway to SQLCLR, we look at the various mechanisms in place to help us control Security. In this Level we will focus on SAFE mode and see how secure SQLCLR is by default. Free eBook - Performance Tuning with DMVsThis free eBook provides you with the core techniques and scripts to monitor your query execution, index usage, session and transaction activity, disk IO, and more. Download the free eBook.

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• ShowPlan Operator of the Week - Merge Join

  Did you ever wonder how and why your indexes affect the performances of joins? Once you've read Fabiano Amorim's unforgettable explanation, you'll learn to love the MERGE operator, and plan your indexes so as to allow the Query Optimiser to use it. Free trial of SQL Backup™“SQL Backup was able to cut down my backup time significantly AND achieved a 90% compression at the same time!” Joe Cheng. Download a free trial now.

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• How would one build a relational database on a key-value store, a-la Berkeley DB's SQL interface?

  - by coleifer

  I've been checking out Berkeley DB and was impressed to find that it supported a SQL interface that is "nearly identical" to SQLite. http://docs.oracle.com/cd/E17076_02/html/bdb-sql/dbsqlbasics.html#identicalusage I'm very curious, at a high-level, how this kind of interface might have been architected. For instance: since values are "transparent", how do you efficiently query and sort by value how are limits and offsets performed efficiently on large result sets how would the keys be structured and serialized for good average-case performance

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• Inherit one instance variable from the global scope

  - by Julian

  I'm using Curses to create a command line GUI with Ruby. Everything's going well, but I have hit a slight snag. I don't think Curses knowledge (esoteric to be fair) is required to answer this question, just Ruby concepts such as objects and inheritance. I'm going to explain my problem now, but if I'm banging on, just look at the example below. Basically, every Window instance needs to have .close called on it in order to close it. Some Window instances have other Windows associated with it. When closing a Window instance, I want to be able to close all of the other Window instances associated with it at the same time. Because associated Windows are generated in a logical fashion, (I append the name with a number: instance_variable_set(self + integer, Window.new(10,10,10,10)) ), it's easy to target generated windows, because methods can anticipate what assosiated windows will be called, (I can recreate the instance variable name from scratch, and almost query it: instance_variable_get(self + integer). I have a delete method that handles this. If the delete method is just a normal, global method (called like this: delete_window(@win543) then everything works perfectly. However, if the delete method is an instance method, which it needs to be in-order to use the self keyword, it doesn't work for a very clear reason; it can 'query' the correct instance variable perfectly well (instance_variable_get(self + integer)), however, because it's an instance method, the global instances aren't scoped to it! Now, one way around this would obviously be to simply make a global method like this: delete_window(@win543). But I have attributes associated with my window instances, and it all works very elegantly. This is very simplified, but it literally translates the problem exactly: class Dog def speak woof end end def woof if @dog_generic == nil puts "@dog_generic isn't scoped when .woof is called from a class method!\n" else puts "@dog_generic is scoped when .woof is called from the global scope. See:\n" + @dog_generic end end @dog_generic = "Woof!" lassie = Dog.new lassie.speak #=> @dog_generic isn't scoped when .woof is called from an instance method!\n woof #=> @dog_generic is scoped when .woof is called from the global scope. See:\nWoof! TL/DR: I need lassie.speak to return this string: "@dog_generic is scoped when .woof is called from the global scope. See:\nWoof!" @dog_generic must remain as an insance variable. The use of Globals or Constants is not acceptable. Could woof inherit from the Global scope? Maybe some sort of keyword: def woof < global # This 'code' is just to conceptualise what I want to do, don't take offence! end Is there some way the .woof method could 'pull in' @dog_generic from the global scope? Will @dog_generic have to be passed in as a parameter?

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