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  • Rails - inheritance hierarchy of classes where an subtipe can play two roles

    - by Miquel
    I need to model Owners and Rentees in an application, so you have stuff that is always owned by someone and can be rented for someone else. I first approached this problem with Single Table Inheritance because both types of person will share all attributes, so you would have a model called Person associated to a table people with Owner and Rentee inheriting from Person. The problem is that Single type inheritance discerns subtypes using a field type and therefore a record in the table can represent either an Owner or a Rentee but not both at the same time, while in the real context you can have an Owner which is renting something from another Owner and therefore that person is at the same time an Owner and a Rentee. How would you approach this problem? Would you use separated tables fro owners and rentees? Is there any other type of table inheritance in Rails?

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  • SQL Server - Select one random record not showing duplicates

    - by Lukes123
    I have two tables, events and photos, which relate together via the 'Event_ID' column. I wish to select ONE random photo from each event and display them. How can I do this? I have the following which displays all the photos which are associated. How can I limit it to one per event? SELECT Photos.Photo_Id, Photos.Photo_Path, Photos.Event_Id, Events.Event_Title, Events.Event_StartDate, Events.Event_EndDate FROM Photos, Events WHERE Photos.Event_Id = Events.Event_Id AND Events.Event_EndDate < GETDATE() AND Events.Event_EndDate IS NOT NULL AND Events.Event_StartDate IS NOT NULL ORDER BY NEWID() Thanks Luke Stratton

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  • Navigating by foreign keys in ADO.NET Entity Framework/MySQL

    - by Werg38
    I am using ASP.NET MVC2 on top of a MySQL database in VS2008. I am using the MySQL ADO.NET connector 6.2.3 to provide the connection for the ADO.NET Entity Data Model. This is mostly working ok, however navigating via foreign keys is causing me a real headache! Here is a simplified example.. Car (Table) CarID PK Colour Doors ManufacturerID FK Manufacturer (Table) ManufacturerID PK Name In the edmx file I can see the 1-many relationship shown as a navigation property in the both the Car and Manufacturer tables. I create a Models.CarRepository that allows me to returns a IQueryable. At the View I want to be able to display the Manufacturer.Name for each car. This is not accessible via the object I get returned. What is best way to implement this? Have I encountered a limitation of the Entity Framework/MySQL combination?

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  • Copy Data from One SQL Server Table to Other in Same Database Without Specifying Columns

    - by Scott
    In SQL Server there is the ability to INSERT all of the data from one table into another using the following statement: INSERT INTO TABLE1 SELECT * FROM TABLE2 When running this on a table with an identity column, even though we have run the command SET IDENTITY_INSERT TABLE1 ON, we get the error: An explicit value for the identity column in table can only be specified when a column list is used and IDENTITY_INSERT is ON This implies that we would have to list off all of the columns within the INSERT in order for this to work properly. In the situation that we are in, we do not have access to the column names, only the list of the tables we need to copy over. Is there any way to get around this limitation?

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  • Finding group maxes in SQL join result

    - by Gene
    Two SQL tables. One contestant has many entries: Contestants Entries Id Name Id Contestant_Id Score -- ---- -- ------------- ----- 1 Fred 1 3 100 2 Mary 2 3 22 3 Irving 3 1 888 4 Grizelda 4 4 123 5 1 19 6 3 50 Low score wins. Need to retrieve current best scores of all contestants ordered by score: Best Entries Report Name Entry_Id Score ---- -------- ----- Fred 5 19 Irving 2 22 Grizelda 4 123 I can certainly get this done with many queries. My question is whether there's a way to get the result with one, efficient SQL query. I can almost see how to do it with GROUP BY, but not quite. In case it's relevant, the environment is Rails ActiveRecord and PostgreSQL.

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  • One table for uploads for multiple resources in CakePHP

    - by Mef
    Hi, I have CakePHP app in which I'd like to attach gallery to multiple resources. Let's say I've got artists, each one has own gallery. I've got articles, every article has some images attached to it and so on. Now I set up tables like this: Artists hasMany Artistimages, fields in artistimages table are: id, artist_id, filename, filetype, filesize etc. Articles hasMany Articleimages, fields in articleimages table are: id, article_id, filename, filetype, filesize etc. ...but this is not how it should be, I think. Is there possibility to have one table called for example uploads which will contain all images with foreign key pointing to resource its reffering to? How to tell CakePHP which image is coming from which resource?

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  • Prevent duplicate rows with all non-unique columns (only with MySQL)?

    - by letseatfood
    Ho do I prevent a duplicate row from being created in a table with two columns, neither of which are unique? And can this be done using MySQL only, or does it require checks with my PHP script? Here is the CREATE query for the table in question (two other tables exist, users and roles): CREATE TABLE users_roles ( user_id INT(100) NOT NULL, role_id INT(100) NOT NULL, FOREIGN KEY (user_id) REFERENCES users(user_id), FOREIGN KEY (role_id) REFERENCES roles(role_id) ) ENGINE = INNODB; I would like the following query, if executed more than once, to throw an error: INSERT INTO users_roles (user_id, role_id) VALUES (1, 2); Please do not recommend bitmasks as an answer. Thanks!

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  • MySQL performance over a (local) network much slower than I would expect

    - by user15241
    MySQL queries in my production environment are taking much longer than I would expect them too. The site in question is a fairly large Drupal site, with many modules installed. The webserver (Nginx) and database server (mysql) are hosted on separated machines, connected by a 100mbps LAN connection (hosted by Rackspace). I have the exact same site running on my laptop for development. Obviously, on my laptop, the webserver and database server are on the same box. Here are the results of my database query times: Production: Executed 291 queries in 320.33 milliseconds. (homepage) Executed 517 queries in 999.81 milliseconds. (content page) Development: Executed 316 queries in 46.28 milliseconds. (homepage) Executed 586 queries in 79.09 milliseconds. (content page) As can clearly be seen from these results, the time involved with querying the MySQL database is much shorter on my laptop, where the MySQL server is running on the same database as the web server. Why is this?! One factor must be the network latency. On average, a round trip from from the webserver to the database server takes 0.16ms (shown by ping). That must be added to every singe MySQL query. So, taking the content page example above, where there are 517 queries executed. Network latency alone will add 82ms to the total query time. However, that doesn't account for the difference I am seeing (79ms on my laptop vs 999ms on the production boxes). What other factors should I be looking at? I had thought about upgrading the NIC to a gigabit connection, but clearly there is something else involved. I have run the MySQL performance tuning script from http://www.day32.com/MySQL/ and it tells me that my database server is configured well (better than my laptop apparently). The only problem reported is "Of 4394 temp tables, 48% were created on disk". This is true in both environments and in the production environment I have even tried increasing max_heap_table_size and Current tmp_table_size to 1GB, with no change (I think this is because I have some BLOB and TEXT columns).

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  • MySQL: Select pages that are not tagged?

    - by lauthiamkok
    Hi, I have a db with two tables like these below, page table pg_id title 1 a 2 b 3 c 4 d tagged table tagged_id pg_id 1 1 2 4 I want to select the pages which are tagged, I tried with this query below but doesn't work, SELECT * FROM root_pages LEFT JOIN root_tagged ON ( root_tagged.pg_id = root_pages.pg_id ) WHERE root_pages.pg_id != root_tagged.pg_id It returns zero - Showing rows 0 - 1 (2 total, Query took 0.0021 sec) But I want it to return pg_id title 2 b 3 c My query must have been wrong?? How can I return the pages which are not tagged correctly? Thanks.

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  • Improving MySQL Update Query Efficiency

    - by Russell C.
    In our database tables we keep a number of counting columns to help reduce the number of simple lookup queries. For example, in our users table we have columns for the number of reviews written, photos uploaded, friends, followers, etc. To help make sure these stay in sync we have a script that runs periodically to check and update these counting columns. The problem is that now that our database has grown significantly the queries we have been using are taking forever to run since they are totally inefficient. I would appreciate someone with more MySQL knowledge than myself to recommend how we can improve it's efficiency: update users set photos=(select count(*) from photos where photos.status="A" AND photos.user_id=users.id) where users.status="A"; If this were a select statement I would just use a join but I'm not sure if that is possible with update. Thanks in advance for your help!

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  • Best tools to create valid XML files from an Excel file

    - by systempuntoout
    I need to create a script that extracts some data from a complex Excel 2003 file (with multiple Sheets and different tables inside a single sheet) and produces different XML files that need to be validated against a given XSD file. My preferred language is Python; to create and validate XML files i would go with lxml. What do you suggest for parsing XSL files? Is xlrd the right tool to use for complex Excel files? Or do i need to convert all the sheets in CSV manually, and read files line by line, splitting and getting data? I accept C#, VB6 suggestions too.

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  • MySQL Join Comma Separated Field

    - by neeraj
    I have two tables. First Table is a batch table that contain comma separated student id in field "batch" batch -------------- id batch -------------- 1 1,2 2 3,4 Second Table is marks marks ---------------------- id studentid subject marks 1 1 English 50 2 2 English 40 3 3 English 70 4 1 Math 65 5 4 English 66 6 5 English 75 7 2 Math 55 How we can find those students of first batch id =1 who have scored more than 45 marks in English without using sub query. Problem i found to get this done using a single query is that we can not use IN as an association operator in JOIN statement What changes are required in below query to make it work? SELECT * FROM batch INNER JOIN marks ON marks.studentid IN(batch.batch) where batch.id = 1

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  • Grails - Need to restrict fetched rows based on condition on join table

    - by sector7
    Hi guys, I have these two domains Car and Driver which have many-to-many relationship. This association is defined in table tblCarsDrivers which has, not surprisingly, primary keys of both the tables BUT additionally also has a new boolean field deleted. Herein lies the problem. When I find/get query on domain Car, I am fetched all related drivers irrespective of their deleted status in tblCarsDrivers, which is expected. I need to put a clause/constraint to exclude the deleted drivers from the list of fetched records. PS: I tried using an association domain CarDriver in joinTable name but that seems not to work. Apparently it expects only table names, not maps. PPS: I know its unnatural to have any other fields besides the mapping keys in mapping table but this is how I got it and it cant be changed. Car domain is defined as such - class Car { Integer id String name static hasMany = [drivers:Driver] static mapping = { table 'tblCars' version false drivers joinTable:[name: 'tblCarsDrivers',column:'driverid',key:'carid'] } } Thanks!

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  • latex table reference

    - by Tim
    Hi, I wrote a long table with a label in a tex file and \input it into my main tex file. The reference in the main tex file to the table, however, does not show the numbering of the table but the one of the next table that are written directly in the main tex file. All long tables that are written directly in the main tex file have correct references. How to fix my problem? Must the label be defined in the same tex file as its reference? Thanks and regards! The label is \label{tab:yy}, and the reference is \ref{tab:yy}, and every table has a distinct label.

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  • Multiple user database design

    - by dieguitoweb
    I have to develop a basic social network for an academic purpose; but I need some tips for the users management.. The users are subdivided into 3 groups with different privilege: admins,analysts and standards users. For every user should be stored into the database the following information: name,lastname,e-mail,age,password. I'm not quite sure how I should design the database between theese two solutions: 1)one table called 'users' with the 'role' attribute that explain what a user can do and what can't do, and the permissions are managed via php 2)every application user is a database user created with the query 'CREATE ROLE' (It's a postgres database) and he has permissions on some tables granted with the 'GRANT' statement You should take into account that the project is for a database exam.. thanks

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  • IF/ELSE makes stored procedure not return a result set

    - by Brendan Long
    I have a stored procedure that needs to return something from one of two databases: IF @x = 1 SELECT @y FROM Table_A ELSE IF @x = 2 SELECT @y FROM Table_B Either SELECT alone will return what I want, but adding the IF/ELSE makes it stop returning anything. I tried: IF @x = 1 RETURN SELECT @y FROM Table_A ELSE IF @x = 2 RETURN SELECT @y FROM Table_B But that causes a syntax error. The two options I see are both horrible: Do a UNION and make sure that only one side has any results: SELECT @y FROM Table_A WHERE @x = 1 UNION SELECT @y FROM Table_B WHERE @x = 2 Create a temporary table to store one row in, and create and delete it every time I run this procedure (lots). Neither solution is elegant, and I assume they would both be horrible for performance (unless MS SQL is smart enough not to search the tables when the WHERE class is always false). Is there anything else I can do? Is option 1 not as bad as I think?

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  • Composite primary keys in N-M relation or not?

    - by BerggreenDK
    Lets say we have 3 tables (actually I have 2 at the moment, but this example might illustrate the thought better): [Person] ID: int, primary key Name: nvarchar(xx) [Group] ID: int, primary key Name: nvarchar(xx) [Role] ID: int, primary key Name: nvarchar(xx) [PersonGroupRole] Person_ID: int, PRIMARY COMPOSITE OR NOT? Group_ID: int, PRIMARY COMPOSITE OR NOT? Role_ID: int, PRIMARY COMPOSITE OR NOT? Should any of the 3 ID's in the relation PersonGroupRole be marked as PRIMARY key or should they all 3 be combined into one composite?? whats the real benefit of doing it or not? I can join anyways as far as I know, so Person JOIN PersonGroupRole JOIN Group gives me which persons are in which Groups etc. I will be using LINQ/C#/.NET on top of SQL-express and SQL-server, so if there is any reasons regarding language/SQL that might make the choice more clear, thats the platform I ask about. Looking forward to see what answers pops up, as I have thought of these primary keys/indexes many times when making combined ones.

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  • database row/ record pointers

    - by David
    Hi I don't know the correct words for what I'm trying to find out about and as such having a hard time googling. I want to know whether its possible with databases (technology independent but would be interested to hear whether its possible with Oracle, MySQL and Postgres) to point to specific rows instead of executing my query again. So I might initially execute a query find some rows of interest and then wish to avoid searching for them again by having a list of pointers or some other metadata which indicates the location on a database which I can go to straight away the next time I want those results. I realise there is caching on databases, but I want to keep these "pointers" else where and as such caching doesn't ultimately solve this problem. Is this just an index and I store the index and look up by this? most of my current tables don't have indexes and I don't want the speed decrease that sometimes comes with indexes. So whats the magic term I've been trying to put into google? Cheers

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  • Getting started with SQLite (Android)

    - by Tarmon
    Hey Everyone, I have limited SQL background, basically a small amount of manipulation through HTML and mostly with pre-existing databases. What I am trying to do is set up a database that will store time information for bus routes. So basically I have different routes with stops for each route and then a list of times that the bus arrives at each stop. Here is an example of a table of times from their website: Link. I am wondering what would be the best way to layout my database/tables? Also what is the purpose of the _id field in each table? Thanks, Rob! P.S. Sorry if my lack of knowledge on the subject has caused me to post a duplicate question.

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  • after running insert or update query, need the last inserted record and compare in vb.net sql server

    - by ereffe
    i have 2 queries in vb.net with an if clause - if x=0 then insert into table1 else update table1 both queries have 5 fields. now what i want to do is after this insert or update takes place, i need to look at this inserted/updated record and compare it with another table (table2). Especially for update, i have 5 fields in both tables. if any of the 5 fields dont match with table2, then i insert a new record in table 2 which is the updated record in table 1. how can i do this?

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  • C# template engine

    - by me
    Hi! I am looking for a stand-alone, easy to use from C# code, template engine. What I want to do is create an html and xml files with placeholders for data, and fill them with data from my code. The engine needs to support loops (duplicating parts of the template form more that one object) and conditions (add parts of the template to the final html/xml only if some conditions are true). Can someone recommend a good option for me, and add a link to more-or-less such code sample, and some documentation about how to use the recommended component for my needs? Thanks:) Just wanted to add one more thing - I also need to use loops to duplicate table rows, or even entire tables (in the html version) and complex elements (in the xml version) Thanks again:)

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  • How do I delete in Django? (mysql transactions)

    - by alex
    If you are familiar with Django, you know that they have a Authentication system with User model. Of course, I have many other tables that have a Foreign Key to this User model. If I want to delete this user, how do I architect a script (or through mysql itself) to delete every table that is related to this user? My only worry is that I can do this manually...but if I add a table , but I forget to add that table to my DELETE operation...then I have a row that links to a deleted, non-existing User.

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  • Dealing with schema upgrades while using Hibernate

    - by nehagp
    I'm using Hibernate as the ORM for my application. I would like to know if there is a good solution to dealing with schema upgrades in my application when these upgrades are done by someone else. For example, I have a set of hbm.xml files and corresponding java classes generated using Hibernate tools. Now in production, everything works fine until the db schema is upgraded (tables/columns may be dropped/added). I do not (my app doesn't) have access to do that so how do I deal with this using Hibernate? Thanks!

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  • Network ActiveRecord relation with Rails

    - by Zag zag..
    Hi, I have a has and belongs to many relation between User and Article models, and I would like to link them even if an article if not hosted on the same database then a user. For example, If an article exists at foo.com/articles/3 and a user exists at bar.com/users/1, If would like to be able to do from foo.com web interface or bar.com web interface this kind of query: a_user.articles (or an_article.users). I think this can be possible adding a field like "url" in users and articles tables. But I don't know how to process for ActiveRecord. My Article model looks like this: class Article < ActiveRecord::Base has_and_belongs_to_many :users end Is there yet some example of project using this kind of relation over internet? Many thanks

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  • Is this an injection attempt or a normal request?

    - by CheeseConQueso
    In cPanel's Analog Stats statistics module, I've noticed countless requests to connect to the following example: /?x=19&y=15 The numbers are random, but its always setting x and y variables. Another category of mysterious requests: /?id=http://nic.bupt.edu.cn/media/j1.txt?? There are other attempts at injections in the request log that have straight sql written into them as well. Example: /jobs/jobinfo.php?id=-999.9 UNION ALL SELECT 1,(SELECT concat(0x7e,0x27,count(table_name),0x27,0x7e) FROM information_schema.tables WHERE table_schema=0x73636363726F6F745F7075626C6963),3,4,5,6,7,8,9,10,11,12,13-- It looks like they are all reaching a 404, but I'm still wondering about the intent behind these. I know this is vague, but maybe someone knows that this is normal while using cPanel & phpMyAdmin services. Also, there was a search box installed on the site which could be the reason. Any suggestions as to what all these are?

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