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  • How to select the nth row in a SQL database table?

    - by Charles Roper
    I'm interested in learning some (ideally) database agnostic ways of selecting the nth row from a database table. It would also be interesting to see how this can be achieved using the native functionality of the following databases: SQL Server MySQL PostgreSQL SQLite Oracle I am currently doing something like the following in SQL Server 2005, but I'd be interested in seeing other's more agnostic approaches: WITH Ordered AS ( SELECT ROW_NUMBER() OVER (ORDER BY OrderID) AS RowNumber, OrderID, OrderDate FROM Orders) SELECT * FROM Ordered WHERE RowNumber = 1000000 Credit for the above SQL: Firoz Ansari's Weblog Update: See Troels Arvin's answer regarding the SQL standard. Troels, have you got any links we can cite?

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  • Deleting orphans with JPA

    - by homaxto
    I have a one-to-one relation where I use CascadeType.PERSIST. This has over time build up a huge amount of child records that has not been deleted, to such an extend that it is reflected in the performance. Now I wish to add some code that cleans up the database removing all the child records that are not referenced by a parent. At the moment we are talking 400K+ records, at I need to run the code on all customer installations just to be sure they do not run into the same problem. I think the best solution would be to run a named query (because we support two databases) that deletes the necessary records, and this is where I get into problems, because how should I write it in JPQL? The result I want can be defined like the following sql statement, which unfortunaltely does not run on MySQL. DELETE FROM child c1 WHERE c1.pk NOT IN (SELECT DISTINCT p.pk FROM child c2 JOIN parent p ON p.child = c2.pk);

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  • What is the Reason large sites don't use MySQL with ASP.NET?

    - by Luke101
    I have read this article from highscalability about stackoverflow and other large websites. Many large high traffic .NET sites such as plentyoffish.com, mysapce and SO all use .NET technologies and use SQL SERver for their database. In the article it says SO said As you add more and more database servers the SQL Server license costs can be outrageous. So by starting scale up and gradually going scale out with non-open source software you can be in a world of financial hurt. I don't understand why don't high traffic .NET sites convert their databases to MySQL as it is waay cheaper then SQL Server

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  • What are the main benefits of implementing a virtual machine as part of an application?

    - by Marplesoft
    Several databases I've been looking at recently implement a virtual machine internally to perform the respective data reads and writes. For an example, check out this article on SQLite's virtual machine they call the 'VDBE'. I'm curious as to what the benefits of such an architecture are. I would assume performance is one but why would a virtual machine like this run faster? In fact, it seems to be that this extra layer could cause it to run slower. So perhaps it's for security? Or portability? Anyway, just curious about this.

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  • Sign Up/Login system for multi-domain/multi-server

    - by David
    I'm thinking about a good solution for implementing a sign up/login system that works across different domains and servers. A working example is Olx (you can register in one domain, and your login will work in the rest of domains). The scenario is that every domain (one per country) has its own database. And there will be 2 servers (for example), each one will have the 50% of the domains (and so the 50% of databases). What would you suggest to start with? Database: MySQL 5.1 Server-side language: PHP 5.3 (I will be using Symfony 1.4, so if someone has some suggestion for this framework, it will be interesting too, although it is optional)

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  • Record locking problem between linux and Windows

    - by PabloG
    I need to run a bunch of old DOS FoxPro / Clipper applications in linux under DOSEMU. The programs access their "databases" located on a network server (could be a Windows or Linux server) Actually, the programs ran fine, but I cannot manage to make the record locking work as supposed: I can run a program in two terminals (or the server and any terminal for instance) and lock the same record in both. Now, I'm using Tiny Core Linux as terminal and Windows XP as server, accesing the shared files via CIFS and the latest DOSEMU (1.4.0), but I tried with various combinations of server (Ubuntu 7 to 9, Damn Small Linux, XP) <- protocol (CIFS, samba, various versions of smbclient) <- client (same as server) with no luck I tried to configure the server part to work without oplocks in samba (after reading the entire O'Reilly Samba book locking chapter in http://oreilly.com/catalog/samba/chapter/book/ch05_05.html ) and in XP (\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\UseOpportunisticLocking = 0) but the problem persist. Any ideas? TIA, Pablo

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  • Major performance difference between two Oracle database instances

    - by jrdioko
    I am working with two instances of an Oracle database, call them one and two. two is running on better hardware (hard disk, memory, CPU) than one, and two is one minor version behind one in terms of Oracle version (both are 11g). Both have the exact same table table_name with exactly the same indexes defined. I load 500,000 identical rows into table_name on both instances. I then run, on both instances: delete from table_name; This command takes 30 seconds to complete on one and 40 minutes to complete on two. Doing INSERTs and UPDATEs on the two tables has similar performance differences. Does anyone have any suggestions on what could have such a drastic impact on performance between the two databases?

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  • How to optimize this user ranking query

    - by James Simpson
    I have 2 databases (users, userRankings) for a system that needs to have rankings updated every 10 minutes. I use the following code to update these rankings which works fairly well, but there is still a full table scan involved which slows things down with a few hundred thousand users. mysql_query("TRUNCATE TABLE userRankings"); mysql_query("INSERT INTO userRankings (userid) SELECT id FROM users ORDER BY score DESC"); mysql_query("UPDATE users a, userRankings b SET a.rank = b.rank WHERE a.id = b.userid"); In the userRankings table, rank is the primary key and userid is an index. Both tables are MyISAM (I've wondered if it might be beneficial to make userRankings InnoDB).

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  • Mapping US zip code to time zone

    - by Doug Kavendek
    When users register with our app, we are able to infer their zip code when we validate them against a national database. What would be the best way to determine a good potential guess of their time zone from this zip code? We are trying to minimize the amount of data we explicitly have to ask them for. They will be able to manually set the time zone later if our best guess is wrong. I realize zip codes won't help with figuring out the time zone outside the US, but in that case we'd have to manually ask anyway, and we deal predominantly with the US regardless. I've found a lot of zip code databases, and so far only a few contain time zone information, but those that do are not free, such as this one. If it's absolutely necessary to pay a subscription to a service in order to do this, then it will not be worth it and we will just have to ask users explicitly. Although language isn't particularly relevant as I can probably convert things however needed, we're using PHP and MySQL.

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  • SQL Server switch to MySQL/PostgreSQL for startup?

    - by chopps
    I just checked out the licensing for SQL Server and well...i can't afford it since im funding this project myself. I have been tinkering with MySQL and PostgreSQL a bit the past few weeks and at this point I can't really decide which to go with. MySQL has a large user base and lots of people using it so finding out how to do various items will not be to hard o find. I will be using ASP.NET with this project. Anyone have experience going from SQL Server to either of these databases? Is one stronger than the other? Thoughts?

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  • SQL Server 2005: When copy table structure to other database "CONSTRAINT" keywords lost

    - by StreamT
    Snippet of original table: CREATE TABLE [dbo].[Batch]( [CustomerDepositMade] [money] NOT NULL CONSTRAINT [DF_Batch_CustomerDepositMade] DEFAULT (0) Snippet of copied table: CREATE TABLE [dbo].[Batch]( [CustomerDepositMade] [money] NOT NULL, Code for copy database: Server server = new Server(SourceSQLServer); Database database = server.Databases[SourceDatabase]; Transfer transfer = new Transfer(database); transfer.CopyAllObjects = true; transfer.CopySchema = true; transfer.CopyData = false; transfer.DropDestinationObjectsFirst = true; transfer.DestinationServer = DestinationSQLServer; transfer.CreateTargetDatabase = true; Database ddatabase = new Database(server, DestinationDatabase); ddatabase.Create(); transfer.DestinationDatabase = DestinationDatabase; transfer.Options.IncludeIfNotExists = true; transfer.TransferData();

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  • Choosing connectionstring in VB.NET application at startup

    - by MatsT
    I have a VB.NET application with a connection to an SQL Server 2003. On the server there are two databases, MyDatabase and MyDatabase_Test. What I would like to do is to show a dialog when the program starts that let's the user choose which database to use. My idea is to create a new form as the starup form that sets this property and then launches the main form. Currently the connectionstring is specified in the application config file. Best would be if I can specify two different connection strings in that file to choose from, but for now it is also acceptable with other solutions like hardcoding the two connectionstrings into the startup form.

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  • What format do I use to store a relatively small amount of user data

    - by wcm
    I am writing a small program for our local high school (pro bono). The program has an interface allows the user to enter school holidays. This is a simple stand alone Windows app. What format should I use to store the data? A big relational data is obviously overkill. My initial plan was to store the data in an XML file. Co-workers have been suggesting that I use JSON files, Access Databases, SQL Lite, and SQL Server Express. There was even a suggestion of old school INI files.

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  • How can I use multiple Datatables on my CrystalReport?

    - by Sergio Tapia
    I have a dataset that connects with three databases. How can I attach my Crystalreport viewer so all three are included? protected void Page_Load(object sender, EventArgs e) { ReportDocument X = new ReportDocument(); DataTable DTable = new DataTable(); DataSet1TableAdapters.TableAdapterManager ????? = new WebApplication1.DataSet1TableAdapters.TableAdapterManager(); DTable = ???????? string ubicacion = Server.MapPath("crystalReport1.rpt"); X.Load(ubicacion); X.SetDataSource(DTable); CrystalReportViewer1.ReportSource = X; }

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  • is there a tool to see the difference between two database tables in SQL Server?

    - by reinier
    What is a good tool to see the differences between 2 tables (or even better, the datasets returned by 2 queries). EDIT: I'm not interested in the schema changes. Just assume that the schemas are the same. background as to why: I'm porting some legacy code which can fill a database with some pre-calced data. The easiest way to see if I got everything right, is to check the output of the old program, with the new one. I was thinking that if there is some kind of 'diff' tool for databases, this might be great.

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  • What is the relationship between IRimTable and PersistenceStore?

    - by Martin
    The BlackBerry Desktop API has the interface IRimTable which apparently maps an "application database" on a BlackBerry device to a virtual structure (i.e, IRimTable has IRimRecords, each of which has IRimField) that developer can browse the handheld device data when it is connected to a desktop computer. Meanwhile, applications in the handheld device can store its data in PersistenceStore databases. The point where I'm stuck is the PersistenceStore API doesn't define any Table or Records or Fields. Does anybody knows what is the relationship between these two classes? And how does the mapping work (if at all) ?

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  • How to deal with 'bad' decision forced on you regarding basic software for your product

    - by raticulin
    Here is my situation, our product used to support several of the major databases. Now management has decided to move all products to MaxDB (aka SapDB previously), and even if we keep supporting some of the previous dbs, all new installations are on MaxDB. I am sure MaxDB is a great db and can support huge SAP installations. But from the point of view of a software developper, its a nightmare. Every time you need to do something not trivial (write an stored procedure, some fancy trigger...) and you google for some info, you get like 0.1% of the hits you would with things like MySql, PostgreSql or MSSql. Mailing lists are nearly non existant. SAP does support it commercially but it is not clear wether we'll buy support. And the decision cannot be rolled back. The product works with MaxDB, but with lots of inefficiency on development and a lot of frustration, is there something one could do?

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  • Database: relational/not relational/object oriented... What to choose?

    - by Damian
    I'm porting a website that I made for app engine to run on a dedicated server. It is coded in java and I'm looking for a database to replace google datastore. My first thougt was MySql because everybody uses it, but i dont like SQL and I think I would feel more comfortable using OODB or anything else. With google datastore I could modify my models and don't worry about the database definition at all. I know using MySql that isn't possible. And I don't want to miss that. And if I use a OODB, which should I use? What about performance compared to MySql? Well, any idea or tip will really help me since I know nothing about databases.

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  • Change connection on the fly

    - by aron
    Hello, I have a SQL server with 50 databases. Each one has the exact same schema. I used the awesome Subsonic 2.2 create the DAL based on one of them. I need to loop though a list of database names and connect to each one and perform an update one at a time. If there a way to alter how subsonic uses the connection string. I believe I would need to store the connection string in memory that way it can keep changing. Is this possible? I tried doing a ConfigurationManager.ConnectionStrings["theConnStrName"].ConnectionString = updated-connection-string-here; .. but that did not work thanks!

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  • Mongodb using db.help() on a particular db command

    - by user1325696
    When I type db.help() It returns DB methods: db.addUser(username, password[, readOnly=false]) db.auth(username, password) ... ... db.printShardingStatus() ... ... db.fsyncLock() flush data to disk and lock server for backups db.fsyncUnock() unlocks server following a db.fsyncLock() I'd like to find out how to get more detailed help for the particular command. The problem was with the printShardingStatus as it returned "too many chunks to print, use verbose if you want to print" mongos> db.printShardingStatus() --- Sharding Status --- sharding version: { "_id" : 1, "version" : 3 } shards: { "_id" : "shard0000", "host" : "localhost:10001" } { "_id" : "shard0001", "host" : "localhost:10002" } databases: { "_id" : "admin", "partitioned" : false, "primary" : "config" } { "_id" : "dbTest", "partitioned" : true, "primary" : "shard0000" } dbTest.things chunks: shard0001 12 shard0000 19 too many chunks to print, use verbose if you want to for ce print I found that for that particular command I can specify boolean parameter db.printShardingStatus(true) which wasn't shown using db.help().

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  • Large tables of static data with DBGhost

    - by Paulo Manuel Santos
    We are thinking of restructuring our database development and deployment processes by using DBGhost, we want to move away from the central development database and bring the database to the source control. One of the problems we have is a big table with static data (containing translated language strings), it has close to 200K rows. I know that our best solution is to move these stings into resource files, but until we implement that, will DbGhost be able to maintain all this static data and generate our development and deployment databases in a short time? And if not is there a good alternative to filling up this table whenever we need to?

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  • How do I diff two spreadsheets?

    - by neu242
    We have a lot of spreadsheets (xls) in our subversion repository. These are usually edited with gnumeric or openoffice.org, and are mostly used to populate databases for unit testing with dbUnit. There are no easy ways of doing diffs on xls files that I know of, and this makes merging extremely tedious and error prone. I've found Spreadsheet Compare, but it requires Excel 2000 or later. I've also tried to convert the spreadsheets to xml and doing a regular diff, but it really feels as a last resort. Are there any tools for diffing two spreadsheets (xls or ods)? I am primarily looking for a multi-platform/open source tool.

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  • How do you access config outside of a request in CherryPy?

    - by OrganicPanda
    I've got a webapp running on CherryPy that needs to access the CherryPy config files before a user creates a request. The docs say to use: host = cherrypy.request.app.config['database']['host'] But that won't work outside of a user request. You can also use the application object when you start the app like so: ... application = cherrypy.tree.mount(root, '/', app_conf) host = application.config['database']['host'] ... But I can see no way of accessing 'application' from other classes outside of a user request. I ask because our app looks at several databases and we set them up when the app starts rather than on user request. I have a feeling this would be useful in other places too; so is there any way to store a reference to 'application' somewhere or access it through the CherryPy API?

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  • How can I use Amazon's API in PHP to search for books?

    - by TerranRich
    I'm working on a Facebook app for book sharing, reviewing, and recommendations. I've scoured the web, searched Google using every search phrase I could think of, but I could not find any tutorials on how to access the Amazon.com API for book information. I signed up for an AWS account, but even the tutorials on their website didn't help me one bit. They're all geared toward using cloud computing for file storage and processing, but that's not what I want. I just want to access their API to search info on books. Kind of like how http://openlibrary.org/ does it, where it's a simple URL call to get information on a book (but their databases aren't nearly as populated as Amazon's). Why is it so damned hard to find the information I need on Amazon's AWS site? If anybody could help, I would greatly appreciate it.

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  • IIS 7 Can't read data from ASP.Net application services tables

    - by vikp
    Hi, I'm working on deploying a web application written in C# with ASP.Net Application services databases. The application runs fine on the development machine. Windows Server 2003 has been built to test the application. The database has been scripted across using MS SQL Server GUI. ASP.Net application services tables were created using an utility. The connection strings are stored in the web.config and connectionStrings.config. The application connects to the database successfully, but then it times out after 10 seconds.

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