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  • SQL - get latest records from table where field is unique

    - by 89stevenharris
    I have a table of data as follows id status conversation_id message_id date_created 1 1 1 72 2012-01-01 00:00:00 2 2 1 87 2012-03-03 00:00:00 3 2 2 95 2012-05-05 00:00:00 I want to get all the rows from the table in date_created DESC order, but only one row per conversation_id. So in the case of the example data above, I would want to get the rows with id 2 and 3. Any advice is much appreciated.

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  • How to represent a 3-way relation with JPA?

    - by simpatico
    A user may have several labels, and links. Then, a user associates a label (or more) to a link. How does one represent the later relationship? A solution could be a many-to-many relationship btw user and link with the optional attribute label. http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns In this case the relationship btw user and label may better be 'virtual'. Any alternative I'm not seeing? PS: I've used google bookmarks terminology, as it matches my case quite well.

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  • Solr automatic startup script

    - by Camran
    I have followed this tutorial: http://wiki.apache.org/solr/SolrJetty But I cant get it working. I don't know what to put in the etc/defaults/jetty file Does anybody know how to configure this? I have Ubuntu 9 Server. Thanks

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  • drawbacks of storing all ''things' in a central table

    - by naiquevin
    Hi, I am not sure if there is a term to describe this, but I have observed that content management systems store all kinds of data in a single table with their bare minimum properties while the meta data is stored in another table in form of key value pairs. for eg. everything (blog posts, pages, images, events etc) is stored in one table and considered as a post. I understand that this allows for abstraction and easy extensibility we are considering designing our new project this way. It is not exactly a CMS but we plan to keep adding modules to it in stages. Lets say initially there will be only posts and images on which comments can be posted. Later on we might add videos which will also have the commenting feature. what are the drawbacks of this approach ? and will it work for a requirement like ours ? Thanks

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  • Why should I abstract my data layer?

    - by Gazillion
    OOP principles were difficult for me to grasp because for some reason I could never apply them to web development. As I developed more and more projects I started understanding how some parts of my code could use certain design patterns to make them easier to read, reuse, and maintain so I started to use it more and more. The one thing I still can't quite comprehend is why I should abstract my data layer. Basically if I need to print a list of items stored in my DB to the browser I do something along the lines of: $sql = 'SELECT * FROM table WHERE type = "type1"';' $result = mysql_query($sql); while($row = mysql_fetch_assoc($result)) { echo '<li>'.$row['name'].'</li>'; } I'm reading all these How-Tos or articles preaching about the greatness of PDO but I don't understand why. I don't seem to be saving any LoCs and I don't see how it would be more reusable because all the functions that I call above just seem to be encapsulated in a class but do the exact same thing. The only advantage I'm seeing to PDO are prepared statements. I'm not saying data abstraction is a bad thing, I'm asking these questions because I'm trying to design my current classes correctly and they need to connect to a DB so I figured I'd do this the right way. Maybe I'm just reading bad articles on the subject :) I would really appreciate any advice, links, or concrete real-life examples on the subject!

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  • SELECT only a certain set of rows at a time

    - by prmatta
    I need to select data from one table and insert it into another table. Currently the SQL looks something like this: INSERT INTO A (x, y, z) SELECT x, y, z FROM B b WHERE ... However, the SELECT is huge, resulting in over 2 millions rows and we think it is taking up too much memory. Informix, the db in this case, runs out of virtual memory when the query is run. How would I go about selecting and inserting a set of rows (say 2000)? Given that I don't think there are any row ids etc.

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  • Hibernate not Loading a class

    - by Noor
    Hi, I have a class Auction that contains a Class Item and Users but when I am getting the class, the class item and Users are not being loaded. Auction Class Mapping File: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated Dec 28, 2010 9:14:12 PM by Hibernate Tools 3.4.0.Beta1 --> <hibernate-mapping> <class name="com.BiddingSystem.Models.Auction" table="AUCTION"> <id name="AuctionId" type="long"> <column name="AUCTIONID" /> <generator class="native" /> </id> <property name="StartTime" type="java.util.Date"> <column name="STARTTIME" /> </property> <property name="EndTime" type="java.util.Date"> <column name="ENDTIME" /> </property> <property name="StartingBid" type="long"> <column name="STARTINGBID" /> </property> <property name="MinIncrement" type="long"> <column name="MININCREMENT" /> </property> <many-to-one name="CurrentItem" class="com.BiddingSystem.Models.Item" fetch="join" cascade="all"> <column name="ItemId" /> </many-to-one> <property name="AuctionStatus" type="java.lang.String"> <column name="AUCTIONSTATUS" /> </property> <property name="BestBid" type="long"> <column name="BESTBID" /> </property> <many-to-one name="User" class="com.BiddingSystem.Models.Users" fetch="join"> <column name="UserId" /> </many-to-one> </class> </hibernate-mapping> When I am doing this: Query query=session.createQuery("from Auction where UserId="+UserId); List <Auction> AllAuctions= new LinkedList<Auction>(query.list()); The Users and Item are null

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  • select a database and in that select tables. using c# . use web config

    - by syedsaleemss
    Im using c# .net windows form application. I have many databases created using sql server Management studio 2005. Each database has several tables. i have a button, when clicked should allow me to select a database among several databases and in that database i want to select a single table. Later i need to display the contents of the selected table into a datagrid view.I came to know that it can be done using Webconfig. How can i acheive this? It goes like this a) select a database b) In that database select a table c) display the contents into a datagridview.

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  • What tool for managing Oracle DB do you suggest?

    - by Artic
    What tool for managing Oracle DB do you suggest? I need to execute scripts and manage data in tables and develop some scripts and packages. I'v tried SQL developer and actually don't like it. Want some more features for developing (debug, code assist, integrated help and so on.)

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  • In django, how can I include some default records in my models.py?

    - by kdt
    If I have a models.py like class WidgetType(models.Model): name = models.CharField(max_length=200) class Widget(models.Model): typeid = models.ForeignKey(WidgetType) data = models.CharField(max_length=200) How can I build in a set of built in constant values for WidgetType when I know I'm only going to have a certain few types of widget? Clearly I could fire up my admin interface and add them by hand, but I'd like to simplify configuration by having it built into the python.

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  • Relation to multiple tables of different types for rating?

    - by Tronic
    i have a table structure like this Products Team Images and want to implement a rating/commenting-feature, where users can rate each entry of all tables. what's the best way to make a single rating table? e.g. a user votes a a product and a team entry, and it should be possible to get alle these entries from a single table. what kind of table-structure is best for this purpose? i hope, my questions is clear enough :/ thanks in advance!

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  • Use DataContext to create schema in an existing blank database file?

    - by jdk
    With a DataContext and a blank file-based database that already exists, is it possible to write the Data Context classes (i.e. the ones I added to the designer) to create the db schema? With a data context I only see the abilities to either: create a new database file and have its structure created at the same time, or to populate data into an existing database having preexisting schema. I'm looking for a hybrid solution between those two worlds. Update 1: My proof that a preexisting db is not compatible with the Data Context CreateDatabase() operation is this error Database 'C:...\App_Data\IntermediateData.mdf' already exists. Choose a different database name. based on this code using (IntermediateClassesDataContext intermediateContext = new IntermediateClassesDataContext(_getIntermediateConn())) { intermediateContext.CreateDatabase(); }

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  • dymanic columns in mysql tables?

    - by fayer
    i want to add dynamic columns in a mysql table. but i dont know exactly how. i want to let the user add some columns (fields) in a thread. eg. let him add a integer field and a value (eg. price: 199) or a string field and a value (eg. name: teddybear). the user can add as many field/value-pairs as he wants. i thought i could create a many-to-many table: thread <- thread_field <- field thread: id, title thread_field: field_id, thread_id, value field: id, name is this a good structure? but in this way i have to set a specific column type of thread_field.value. either its an integer or a string. i want to have the possibility to have it dymanic, let the user choose. how can i do this? thanks!

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  • OpenGL code to render ribbon diagrams for protein

    - by eipxen
    Hey all, I am looking to render ribbon diagrams of proteins using OpenGL and C++. Does anyone know if any open source code for this already exists, or if there are good guides to do this? If not, I'd prefer to figure it out myself ;) but I didn't want to reinvent the wheel, especially if the wheel was free.

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  • Trying to create fields based on a case statement

    - by dido
    I'm having some trouble with the query below. I am trying to determine if the "category" field is A, B or C and then creating a field based on the category. That field would sum up payments field. But I'm running into error saying "incorrect syntax near keyword As". I am creating this in a SQL View. Using SQL Server 2008 SELECT r.id, r.category CASE WHEN r.category = 'A' then SUM(r.payment) As A_payments WHEN r.category = 'B' then SUM(r.payment) As B_payments WHEN r.category = 'C' then SUM(r.payment) As C_payments END FROM r_invoiceTable As r GROUP BY r.id, r.category I have data where all of the above cases should be executed because the data that I have has A,B and C Sample Data- r_invoiceTable Id --- Category ---- Payment 222 A ---- 50 444 A ---- 30 111 B ---- 90 777 C ---- 20 555 C ---- 40 Desired Output A_payments = 80, B_payments = 90, C_payments = 60

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  • DB management for Heroku apps

    - by zetarun
    Hi all, I'm fairly new to both Rails and Heroku but I'm seriously thinking of using it as a platform to deploy my Ruby/Rails applications. I want to use all the power of Heroku, so I prefer the "embedded" PostgreSQL managed by Heroku instead of the addon for Amazon RDS for MySQL, but I'm not so confident without the possibility to access my data in a SQL client... I know that in a well made app you have no need to access DB, but there are some situations (add rows to a config table, see data not mapped in a view, update some columns for debugging issues, performance monitoring, running queries for reporting, etc.) when this can be good... How do you solve this problem? What's you experience in a real life app powered by Heroku? Thanks!

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  • PHP - How to retrieve session in php

    - by Klaus Jasper
    I created a table that contains id - names - jobs and page that shows the names only and beside each name there is button Job and session that contains the id. this is my code $query = mysql_query("SELECT * FROM table"); while($fetch = mysql_fetch_array("$query")){ $name = $fetch['names']; $id = $fetch['id']; echo '</br>'; echo $name; $_SESSION['name'] = $id; echo "<button>Job</button>"; } I want when the user click on button Job redirect to a page that contains the job of that session. so how can I do it?

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  • MySQL Query to get count of unique values?

    - by RD
    Hits Table: hid | lid | IP 1 | 1 | 123.123.123.123 2 | 1 | 123.123.123.123 3 | 2 | 123.123.123.123 4 | 2 | 123.123.123.123 5 | 2 | 123.123.123.124 6 | 2 | 123.123.123.124 7 | 3 | 123.123.123.124 8 | 3 | 123.123.123.124 9 | 3 | 123.123.123.124 As you can see, there following are the unique hits for the various lid: lid 1: 1 unique hit lid 2: 2 unique hits lid 3: 1 unique hit So basically, I need a query that will return the following: lid | uhits | 1 | 1 | 2 | 2 | 3 | 1 | Anybody know how to get that?

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  • Mysql query question

    - by brux
    I have 2 tables: Customer: customerid - int, pri-key,auto fname - varchar sname -varchar housenum - varchar street -varchar Items: itemid - int,pri-key,auto type - varchar collectiondate - date releasedate - date customerid - int I need a query which will get me all items that have a releasedate 3 days prior to (and including) the current date. i.e The query should return customerid,fname,sname,street,housenum,type,releasedate for all items which have releasedate within (and including)3 days prior today thanks in advance

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  • MySQL foreign key constraint disappearing

    - by Bramjam
    This is my table: /* oefenreeks leerplan */ CREATE TABLE leerplan_oefenreeks ( leerplan_oefenreeks_id INT PRIMARY KEY AUTO_INCREMENT NOT NULL, leerplan_id INT NOT NULL, oefenreeks_id INT NOT NULL, plaats INT NOT NULL ); /* fk */ ALTER TABLE leerplan_oefenreeks ADD CONSTRAINT fk_leerp_oefenr_leerplan FOREIGN KEY(leerplan_id) REFERENCES leerplan (leerplan_id) ON DELETE CASCADE; ALTER TABLE leerplan_oefenreeks ADD CONSTRAINT fk_leerp_oefenr_oefenreeks FOREIGN KEY(oefenreeks_id) REFERENCES oefenreeks (oefenreeks_id) ON DELETE CASCADE; /* when I execute the nexline, my fk_leerp_oefenr_leerplan constraint vanishes/disappears*/ ALTER TABLE leerplan_oefenreeks ADD CONSTRAINT un_leerp_oefenr UNIQUE(leerplan_id, oefenreeks_id); ALTER TABLE leerplan_oefenreeks ADD CONSTRAINT un_leerp_oefenr_plaats UNIQUE(leerplan_id, plaats); When I go and check only 3 constraints exist. fk_leerp_oefenr_leerplan disappears. I don't understand why this happens.

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