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  • Converting a certain SQL query into relational algebra

    - by Fumler
    Just doing an assignment for my database course and I just want to double check that I've correctly wrapped my head around relational algebra. The SQL query: SELECT dato, SUM(pris*antall) AS total FROM produkt, ordre WHERE ordre.varenr = produkt.varenr GROUP BY dato HAVING total >= 10000 The relational algebra: stotal >= 10000( ?R(dato, total)( sordre.varenr = produkt.varenr( datoISUM(pris*antall(produkt x ordre)))) Is this the correct way of doing it?

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  • Hibernate and default values

    - by Schildmeijer
    Is it possible to use annotations to map a default value for a column? eg. I have a column named 'date' which is supposed to be '0000-00-00 00:00:00' if not date is explicitly given. I know I can add this to the ctor of the Entity. But then the default behavior will no be present in my database backend. (eg. Default column in mysql)

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  • Android Proxy Cursor

    - by Alxandr
    I have a database with which I wish to expose data with a ContentProvider. However, it is important that all the colums are not exposed, and also they should be renamed. Is there any good way of doing this? I was thinking maybe some kind of proxy-cursor which takes a cursor and translates its columns to the desired ones, and calls to close and the like would just be replayed to the original cursor. Does something like this exist, or would it be hard to make?

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  • Find and replace table/field names in Access?

    - by richardtallent
    I've been handed a rather large, old, and crusty Access 2000/2003 database to clean up. I'll need to rename a number of tables and fields, but need to do so in a way that doesn't break existing queries. (Fortunately, there are no macros, forms, or reports to worry about.) I've heard there are some commercial tools to make this job easier, but only found one (http://www.rickworld.com/products.html). Can anyone recommend this software, or any alternatives?

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  • De-normalization for the sake of reports - Good or Bad?

    - by Travis
    What are the pros/cons of de-normalizing an enterprise application database because it will make writing reports easier? Pro - designing reports in SSRS will probably be "easier" since no joins will be necessary. Con - developing/maintaining the app to handle de-normalized data will become more difficult due to duplication of data and synchronization. Others?

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  • How do I design this link table?

    - by Soo
    Ok SO, I have a user table and want to define groups of users together. The best solution I have for this is to create three database tables as follows: UserTable user_id user_name UserGroupLink group_id member_id GroupInfo group_id group_name This method keeps the member and group information separate. This is just my way of thinking. Is there a better way to do this? Also, what is a good naming convention for tables that link two other tables?

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  • get renamed file names of multiple upload form [js array] in codeigniter

    - by artmania
    Hi friends, I use codeigniter. I have a multiple image upload form. The code below is working well for uploading, but I also need to save file names to database. How can I get the names in here? I spent hours & hours :/ but could not sort it :/ Appreciate helps!!! uploadform.php echo form_open_multipart('gallery/upload'); <input type="file" name="photo" size="50" /> <input type="file" name="thumb" size="50" /> <input type="submit" value="Upload" /> </form> I have a controller between form view and model load model (of course : )) but didnt post here because of no need. gallery_model.php function multiple_upload($upload_dir = 'uploads/', $config = array()) { /* Upload */ $CI =& get_instance(); $files = array(); if(empty($config)) { $config['upload_path'] = realpath($upload_dir); $config['allowed_types'] = 'gif|jpg|jpeg|jpe|png'; $config['max_size'] = '2048'; } $CI->load->library('upload', $config); $errors = FALSE; foreach($_FILES as $key => $value) { if( ! empty($value['name'])) { if( ! $CI->upload->do_upload($key)) { $data['upload_message'] = $CI->upload->display_errors(ERR_OPEN, ERR_CLOSE); // ERR_OPEN and ERR_CLOSE are error delimiters defined in a config file $CI->load->vars($data); $errors = TRUE; } else { // Build a file array from all uploaded files $files[] = $CI->upload->data(); } } } // There was errors, we have to delete the uploaded files if($errors) { foreach($files as $key => $file) { @unlink($file['full_path']); } } elseif(empty($files) AND empty($data['upload_message'])) { $CI->lang->load('upload'); $data['upload_message'] = ERR_OPEN.$CI->lang->line('upload_no_file_selected').ERR_CLOSE; $CI->load->vars($data); } else { return $files; } /* ------------------------------- Insert to database */ // problem is here, i need file names to add db. // if there is already same names file at the folder, it rename file itself. so in such case, I need renamed file name :/ } }

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  • Need a good way to store data in a DB from a table on a webpage that can have N columns.

    - by Abe Miessler
    Users need to be able to add a specific type of column to an otherwise static table on my web page and then save the information they enter in there to the database. I've been told that in reality they will almost never go over 5 columns but I would rather support N. The columns will all be of the same datatype. My first thought was to have an XML column with the values from all added columns in there but I was curious if anyone else had come up with a better solution. Suggestions?

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  • Data retrieval and Join operations with cluster db server

    - by Goerge
    If any database spreads across multiple servers (ex. Microsoft Sql Server), how can we do join or filter operations. In my scenario, if suppose: A single table spreads across multiple servers how can we filter rows based on user input? If master table is there on one db server and transaction table is at another db server, how can we do join operations? Please let me know how can we achieve this and where can I get more details about this?

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  • Any SMO Library for .NET?

    - by gtas
    Anyone knows any library for SQL Server database backup and restore for .NET? This actually is needed to avoid writing one new. There is so many people out there giving their libraries, but i found it strange i couldn't came up with googling anything related.

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  • mysql error #1452 appearing when trying to add a constraint

    - by user1701484
    I am trying to alter a table so That I can add a foreign key constraint in mysql database: ALTER TABLE `Question` ADD CONSTRAINT `FK_question` FOREIGN KEY (`QuestionId`) REFERENCES `Image_Question` (`QuestionId`) ON DELETE CASCADE ; Problem is that it is giving me this error: 1452 - Cannot add or update a child row: a foreign key constraint fails (mobile_app. '#sql-4517_15241', CONSTRAINT FK_question FOREIGN KEY (QuestionId) REFERENCES Image_Question (QuestionId) ON DELETE CASCADE) What does this error actually mean and what are the possible solutions I might have to undertake in order to fix this?

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  • iPhone SQLite connection in domain object - close each time?

    - by BahaiResearch.com
    I have what I would consider a small sized iPhone app that uses SQLite. There is a singleton domain object which gets data from a SQLite database. Is it better to create and open the SQLite connection for each request, or to open the DB once and hold on to it for the duration of the app. The app's reason for being is the domain object so other objects will not need the DB.

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  • How to implement geo-based data store and computation?

    - by Mickey Shine
    Well, let me explain this briefly: 1.I want to build a website that provides location based services, like http://fireeagle.yahoo.net/ . 2.I guess most of these services have something do with longitude and latitude. 3.Is there any particular database/datastore/data structures fit well for such apps? I mean easy to store longitude, latitude and easy to compute or easy to use. I am new to this and any feedbacks are welcome

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  • python django automated data addition

    - by zubin71
    I have a script which reads data from a csv file. I need to store the data into a database which has already been created as $ python manage.py syncdb so, that automated data entry is possible in an easier manner, as available in the django shell.

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  • Memcache vs MySQL in memory

    - by TimK
    I have a database that won't grow much in size. It's current size is about 1 GB. Achieving the fastest performance is desired. Question: When should I use Memcache vs simply using MySQL Innodb ability to store all my content within RAM (innodb_buffer_pool_size)?

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  • Java DriverManager Always Assigns My Driver

    - by JGB146
    I am writing a driver to act as a wrapper around two separate MySQL connections (to distributed databases). Basically, the goal is to enable interaction with my driver for all applications instead of requiring the application to sort out which database holds the desired data. Most of the code for this is in place, but I'm having a problem in that when I attempt to create connections via the MySQL Driver, the DriverManager is returning an instance of my driver instead of the MySQL Driver. I'd appreciate any tips on what could be causing this and what could be done to fix it! Below is a few relevant snippets of code. I can provide more, but there's a lot, so I'd need to know what else you want to see. First, from MyDriver.java: public MyDriver() throws SQLException { DriverManager.registerDriver(this); } public Connection connect(String url, Properties info) throws SQLException { try { return new MyConnection(info); } catch (Exception e) { return null; } } public boolean acceptsURL(String url) throws SQLException { if (url.contains("jdbc:jgb://")) { return true; } return false; } It is my understanding that this acceptsURL function will dictate whether or not the DriverManager deems my driver a suitable fit for a given URL. Hence it should only be passing connections from my driver if the URL contains "jdbc:jgb://" right? Here's code from MyConnection.java: Connection c1 = null; Connection c2 = null; /** *Constructors */ public DDBSConnection (Properties info) throws SQLException, Exception { info.list(System.out); //included for testing Class.forName("com.mysql.jdbc.Driver").newInstance(); String url1 = "jdbc:mysql://server1.com/jgb"; String url2 = "jdbc:mysql://server2.com/jgb"; this.c1 = DriverManager.getConnection( url1, info.getProperty("username"), info.getProperty("password")); this.c2 = DriverManager.getConnection( url2, info.getProperty("username"), info.getProperty("password")); } And this tells me two things. First, the info.list() call confirms that the correct user and password are being sent. Second, because we enter an infinite loop, we see that the DriverManager is providing new instances of my connection as matches for the mysql URLs instead of the desired mysql driver/connection. FWIW, I have separately tested implementations that go straight to the mysql driver using this exact syntax (al beit only one at a time), and was able to successfully interact with each database individually from a test application outside of my driver.

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