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• How to represent a Many-To-Many relationship in XML or other simple file format?

  - by CSharperWithJava

  I have a list management appliaction that stores its data in a many-to-many relationship database. I.E. A note can be in any number of lists, and a list can have any number of notes. I also can export this data to and XML file and import it in another instance of my app for sharing lists between users. However, this is based on a legacy system where the list to note relationship was one-to-many (ideal for XML). Now a note that is in multiple lists is esentially split into two identical rows in the DB and all relation between them is lost. Question: How can I represent this many-to-many relationship in a simple, standard file format? (Preferably XML to maintain backwards compatibility)

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• Best datastructure for this relationship...

  - by Travis

  I have a question about database 'style'. I need a method of storing user accounts. Some users "own" other user accounts (sub-accounts). However not all user accounts are owned, just some. Is it best to represent this using a table structure like so... TABLE accounts ( ID ownerID -> ID name ) ...even though there will be some NULL values in the ownerID column for accounts that do not have an owner. Or would it be stylistically preferable to have two tables, like so. TABLE accounts ( ID name ) TABLE ownedAccounts ( accountID -> accounts(ID) ownerID -> accounts(ID) ) Thanks for the advice.

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• Unique constraint on more than 10 columns

  - by tk

  I have a time-series simulation model which has more than 10 input variables. The number of distinct simulation instances would be more than 1 million, and each simulation instance generates a few output rows every day. To save the simulation result in a relational database, i designed tables like this. Table SimulationModel { simul_id : integer (primary key), input0 : string or numeric, input1 : string or numeric, ...} Table SimulationOutput { dt : DateTime (primary key), simul_id : integer (primary key), output0 : numeric, ...} My question is, is it fine to put an unique constraint on all of the input columns of SimulationModel table? If it is not a good idea, then what kind of other options do i have to make sure each model is unique?

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• Should I Split Tables Relevant to X Module Into Different DB? Mysql

  - by Michael Robinson

  I've inherited a rather large and somewhat messy codebase, and have been tasked with making it faster, less noodly and generally better. Currently we use one big database to hold all data for all aspects of the site. As we need to plan for significant growth in the future, I'm considering splitting tables relevant to specific sections of the site into different databases, so if/when one gets too large for one server I can more easily migrate some user data to different mysql servers while retaining overall integrity. I would still need to use joins on some tables across the new databases. Is this a normal thing to do? Would I incur a performance hit because of this?

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• How should I build a simple database package for my python application?

  - by Carson Myers

  I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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• How to find foreign-key dependencies pointing to one record in Oracle?

  - by daveslab

  Hi folks, I have a very large Oracle database, with many many tables and millions of rows. I need to delete one of them, but want to make sure that dropping it will not break any other dependent rows that point to it as a foreign key record. Is there a way to get a list of all the other records, or at least table schemas, that point to this row? I know that I could just try to delete it myself, and catch the exception, but I won't be running the script myself and need it to run clean the first time through. I have the tools SQL Developer from Oracle, and PL/SQL Developer from AllRoundAutomations at my disposal. Thanks in advance!

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• Options for storing large text blobs in/with an SQL database?

  - by kdt

  Hi, I have some large volumes of text (log files) which may be very large (up to gigabytes). They are associated with entities which I'm storing in a database, and I'm trying to figure out whether I should store them within the SQL database, or in external files. It seems like in-database storage may be limited to 4GB for LONGTEXT fields in MySQL, and presumably other DBs have similar limits. Also, storing in the database presumably precludes any kind of seeking when viewing this data -- I'd have to load the full length of the data to render any part of it, right? So it seems like I'm leaning towards storing this data out-of-DB: are my misgivings about storing large blobs in the database valid, and if I'm going to store them out of the database then are there any frameworks/libraries to help with that? (I'm working in python but am interested in technologies in other languages too)

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• Parse HTML Offline

  - by Clark Gable

  Are there any HTML parsers that parse HTML docs offline, i.e. stored on your computer? If so, can anyone name some good ones please?

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• Force ClickOnce - application to be started offline?

  - by stormianrootsolver

  I have a click once application here that needs to be started offline exclusively sometimes. Reason is that it needs to be started VERY early during boot, at a point when there is no network connection yet, also it must not wait for any network connectivity. I know, this requirement seems strange, but it has legacy reasons. What do you think?

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• Need a field / flag / status number for mutliple use ?

  - by Jules

  I want to create a field in my database which will be easy to query. I think if I give a bit of background this will make more sense. My table has listings shown on my website. I run a program which looks at the listings a decides whether to hide them from being shown on the site. I also hide listings manually for various reasons. I want to store these reasons in a field, so more than one reason could be made for hiding. So I need some form of logic to determine which reasons have been used. Can anyone offer me any guidance on what will be future-proof aka new reasons and what will be quick and easy to query upon ?

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• Three customer addresses in one table or in separate tables?

  - by DR

  In my application I have a Customer class and an Address class. The Customer class has three instances of the Address class: customerAddress, deliveryAddress, invoiceAddress. Whats the best way to reflect this structure in a database? The straightforward way would be a customer table and a separate address table. A more denormalized way would be just a customer table with columns for every address (Example for "street": customer_street, delivery_street, invoice_street) What are your experiences with that? Are there any advantages and disadvantages of these approaches?

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• how to design a db like Facebook where users can update their status and of the fb page as admin

  - by Harsha M V

  i am designing a database where users can update status messages of theirs and they can create pages groups like facebook fan page and post status like the admin of the page and not as a user. user(id, name..) group(id, name...) group_admin(group_id, user_id) this is my set up. Is this the way to do it. How to post under the group as an admin. will i need to make a check to every user if he is the admin or not ?

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• SQL Server: Log file grows more and more, and do not get merged with the MDF file

  - by SDReyes

  My database files look very suspicious. we are using the DB in a production stage. and I'm seeing how the LDF file grows more and more. while the MDF file seems as it is not growing at all (I don't have a file size history to demonstrate it, but I think it is not doing it!! I bet!) So I guess what could be happening? How could I force the merge to the MDF?

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• Killing Self-resurrecting Files

  - by Zian Choy

  Local computer: Dell desktop Windows XP Named "5" Server: Windows Server 2008 Named "W" Whenever I delete a file, log out, and log in, the file reappears. The files all supposedly live on the server (e.g. "\W\Home$\zchoy\Desktop") but even when the files are deleted from the server and the local computer, they come back. I've already tried resetting the offline files cache. I tried deleting a file and then synchronizing with the server. The file didn't come back. However, as mentioned earlier, the file comes back once I log out and log in.

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• How the "migrations" approach makes database continuous integration possible

  - by David Atkinson

  Testing a database upgrade script as part of a continuous integration process will only work if there is an easy way to automate the generation of the upgrade scripts. There are two common approaches to managing upgrade scripts. The first is to maintain a set of scripts as-you-go-along. Many SQL developers I've encountered will store these in a folder prefixed numerically to ensure they are ordered as they are intended to be run. Occasionally there is an accompanying document or a batch file that ensures that the scripts are run in the defined order. Writing these scripts during the course of development requires discipline. It's all too easy to load up the table designer and to make a change directly to the development database, rather than to save off the ALTER statement that is required when the same change is made to production. This discipline can add considerable overhead to the development process. However, come the end of the project, everything is ready for final testing and deployment. The second development paradigm is to not do the above. Changes are made to the development database without considering the incremental update scripts required to effect the changes. At the end of the project, the SQL developer or DBA, is tasked to work out what changes have been made, and to hand-craft the upgrade scripts retrospectively. The end of the project is the wrong time to be doing this, as the pressure is mounting to ship the product. And where data deployment is involved, it is prudent not to feel rushed. Schema comparison tools such as SQL Compare have made this latter technique more bearable. These tools work by analyzing the before and after states of a database schema, and calculating the SQL required to transition the database. Problem solved? Not entirely. Schema comparison tools are huge time savers, but they have their limitations. There are certain changes that can be made to a database that can't be determined purely from observing the static schema states. If a column is split, how do we determine the algorithm required to copy the data into the new columns? If a NOT NULL column is added without a default, how do we populate the new field for existing records in the target? If we rename a table, how do we know we've done a rename, as we could equally have dropped a table and created a new one? All the above are examples of situations where developer intent is required to supplement the script generation engine. SQL Source Control 3 and SQL Compare 10 introduced a new feature, migration scripts, allowing developers to add custom scripts to replace the default script generation behavior. These scripts are committed to source control alongside the schema changes, and are associated with one or more changesets. Before this capability was introduced, any schema change that required additional developer intent would break any attempt at auto-generation of the upgrade script, rendering deployment testing as part of continuous integration useless. SQL Compare will now generate upgrade scripts not only using its diffing engine, but also using the knowledge supplied by developers in the guise of migration scripts. In future posts I will describe the necessary command line syntax to leverage this feature as part of an automated build process such as continuous integration.

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• Data Synchronization in mobile apps - multiple devices, multiple users

  - by ProgrammerNewbie

  I'm looking into building my first mobile app. One of the core features of the application is that multiple devices/users will have access to the same data -- and all of them will have CRUD rights. I believe the architecture should involve a central server where all the data is stored. The devices will use an API to interact with the server to perform its data operations (e.g. adding a record, editing a record, deleting a record). I imagine a scenario where synchronizing the data will become a problem. Assume the application should work when it is not connected to the Internet, and thus cannot communicate with this central server. So: User A is offline and edits record #100 User B is offline and edits record #100 User C is offline and deletes record #100 User C goes online (presumably, record #100 should get deleted on the server) User A and B goes online, but the records they edited no longer exist All sorts of scenarios similar to the above can come up. How is this generally handled? I plan to use MySQL, but am wondering if it's not appropriate for such a problem.

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• Best pattern for storing (product) attributes in SQL Server

  - by EdH

  We are starting a new project where we need to store product and many product attributes in a database. The technology stack is MS SQL 2008 and Entity Framework 4.0 / LINQ for data access. The products (and Products Table) are pretty straightforward (a SKU, manufacturer, price, etc..). However there are also many attributes to store with each product (think industrial widgets). These may range from color to certification(s) to pipe size. Every product may have different attributes, and some may have multiples of the same attribute (Ex: Certifications). The current proposal is that we will basically have a name/value pair table with a FK back to the product ID in each row. An example of the attributes Table may look like this: ProdID AttributeName AttributeValue 123 Color Blue 123 FittingSize 1.25 123 Certification AS1111 123 Certification EE2212 123 Certification FM.3 456 Pipe 11 678 Color Red 999 Certification AE1111 ... Note: Attribute name would likely come from a lookup table or enum. So the main question here is: Is this the best pattern for doing something like this? How will the performance be? Queries will be based on a JOIN of the product and attributes table, and generally need many WHEREs to filter on specific attributes - the most common search will be to find a product based on a set of known/desired attributes. If anyone has any suggestions or a better pattern for this type of data, please let me know. Thanks! -Ed

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• Struggling with a data modeling problem

  - by rpat

  I am struggling with a data model (I use MySQL for the database). I am uneasy about what I have come up with. If someone could suggest a better approach, or point me to some reference matter I would appreciate it. The data would have organizations of many types. I am trying to do a 3 level classification (Class, Category, Type). Say if I have 'Italian Restaurant', it will have the following classification Food Services Restaurants Italian However, an organization may belong to multiple groups. A restaurant may also serve Chinese and Italian. So it will fit into 2 classifications Food Services Restaurants Italian Food Services Restaurants Chinese The classification reference tables would be like the following: ORG_CLASS (RowId, ClassCode, ClassName) 1, FOOD, Food Services ORG_CATEGORY(RowId, ClassCode, CategoryCode, CategoryName) 1, FOOD, REST, Restaurants ORG_TYPE (RowId, ClassCode, CategoryCode, TypeCode, TypeName) 100, FOOD, REST, ITAL, Italian 101, FOOD, REST, CHIN, Chinese 102, FOOD, REST, SPAN, Spanish 103, FOOD, REST, MEXI, Mexican 104, FOOD, REST, FREN, French 105, FOOD, REST, MIDL, Middle Eastern The actual data tables would be like the following: I will allow an organization a max of 3 classifications. I will have 3 GroupIds each pointing to a row in ORG_TYPE. So I have my ORGANIZATION_TABLE ORGANIZATION_TABLE (OrgGroupId1, OrgGroupId2, OrgGroupId3, OrgName, OrgAddres) 100,103,NULL,MyRestaurant1, MyAddr1 100,102,NULL,MyRestaurant2, MyAddr2 100,104,105, MyRestaurant3, MyAddr3 During data add, a dialog could let the user choose the clssa, category, type and the corresponding GroupId could be populated with the rowid from the ORG_TYPE table. During Search, If all three classification are chosen, It will be more specific. For example, if Food Services Restaurants Italian is the criteria, the where clause would be 'where OrgGroupId1 = 100' If only 2 levels are chosen Food Services Restaurants I have to do 'where OrgGroupId1 in (100,101,102,103,104,105, .....)' - There could be a hundred in that list I will disallow class level search. That is I will force selection of a class and category The Ids would be integers. I am trying to see performance issues and other issues. Overall, would this work? or I need to throw this out and start from scratch.

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• Graph-structured databases and Php

  - by stagas

  I want to use a graph database using php. Can you point out some resources on where to get started? Is there any example code / tutorial out there? Or are there any other methods of storing data that relate to each other in totally random/abstract situations? - Very abstract example of the relations needed: John relates to Mary, both relate to School, John is Tall, Mary is Short, John has Blue Eyes, Mary has Green Eyes, query I want is which people are related to 'Short people that have Green Eyes and go to School' - answer John - Another example: TrackA -> ArtistA -> ArtistB -> AlbumA -----> [ label ] -> AlbumB -----> [ A ] -> TrackA:Remix -> Genre:House -> [ Album ] -----> [ label ] TrackB -> [ C ] [ B ] Example queries: Which Genre is TrackB closer to? answer: House - because it's related to Album C, which is related to TrackA and is related to Genre:House Get all Genre:House related albums of Label A : result: AlbumA, AlbumB - because they both have TrackA which is related to Genre:House - It is possible in MySQL but it would require a fixed set of attributes/columns for each item and a complex non-flexible query, instead I need every attribute to be an item by itself and instead of 'belonging' to something, to be 'related' to something.

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• Building a News-feed that comprises posts "created by user's connections" && "on the topics user is following"

  - by aklin81

  I am working on a project of Questions & Answers website that allows a user to follow questions on certain topics from his network. A user's news-feed wall comprises of only those questions that have been posted by his connections and tagged on the topics that he is following(his expertise topics). I am confused what database's datamodel would be most fitting for such an application. The project needs to consider the future provisions for scalability and high performance issues. I have been looking at Cassandra and MySQL solutions as of now. After my study of Cassandra I realized that Simple news-feed design that shows all the posts from network would be easy to design using Cassandra by executing fast writes to all followers of a user about the post from user. But for my kind of application where there is an additional filter of 'followed topics', (ie, the user receives posts "created by his network" && "on topics user is following"), I could not convince myself with a good schema design in Cassandra. I hope if I missed something because of my short understanding of cassandra, perhaps, can you please help me out with your suggestions of how this news-feed could be implemented in Cassandra ? Looking for a great project with Cassandra ! Edit: There are going to be maximum 5 tags allowed for tagging the question (ie, max 5 topics can be tagged on a question).

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• Modifying my website to allow anonymous comments

  - by David

  I write the code for my own website as an educational/fun exercise. Right now part of the website is a blog (like every other site out there :-/) which supports the usual basic blog features, including commenting on posts. But I only have comments enabled for logged-in users; I want to alter the code to allow anonymous comments - that is, I want to allow people to post comments without first creating a user account on my site, although there will still be some sort of authentication involved to prevent spam. Question: what information should I save for anonymous comments? I'm thinking at least display name and email address (for displaying a Gravatar), and probably website URL because I eventually want to accept OpenID as well, but would anything else make sense? Other question: how should I modify the database to store this information? The schema I have for the comment table is currently comment_id smallint(5) // The unique comment ID post_id smallint(5) // The ID of the post the comment was made on user_id smallint(5) // The ID of the user account who made the comment comment_subject varchar(128) comment_date timestamp comment_text text Should I add additional fields for name, email address, etc. to the comment table? (seems like a bad idea) Create a new "anonymous users" table? (and if so, how to keep anonymous user ids from conflicting with regular user ids) Or create fake user accounts for anonymous users in my existing users table? Part of what's making this tricky is that if someone tries to post an anonymous comment using an email address (or OpenID) that's already associated with an account on my site, I'd like to catch that and prompt them to log in.

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• Schema design: many to many plus additional one to many

  - by chrisj

  Hi, I have this scenario and I'm not sure exactly how it should be modeled in the database. The objects I'm trying to model are: teams, players, the team-player membership, and a list of fees due for each player on a given team. So, the fees depend on both the team and the player. So, my current approach is the following: **teams** id name **players** id name **team_players** id player_id team_id **team_player_fees** id team_players_id amount send_reminder_on Schema layout ERD In this schema, team_players is the junction table for teams and players. And the table team_player_fees has records that belong to records to the junction table. For example, playerA is on teamA and has the fees of $10 and $20 due in Aug and Feb. PlayerA is also on teamB and has the fees of $25 and $25 due in May and June. Each player/team combination can have a different set of fees. Questions: Are there better ways to handle such a scenario? Is there a term for this type of relationship? (so I can google it) Or know of any references with similar structures?

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• smallest mysql type that accomodates single decimal

  - by donpal

  Database newbie here. I'm setting up a mysql table. One of the fields will accept a value in increment of a 0.5. e.g. 0.5, 1.0, 1.5, 2.0, .... 200.5, etc. I've tried int but it doesn't capture the decimals. `value` int(10), What would be the smallest type that can accommodate this value, considering it's only a single decimal. I also was considering that because the decimal will always be 0.5 if at all, I could store it in a separate boolean field? So I would have 2 fields instead. Is this a stupid or somewhat over complicated idea? I don't know if it really saves me any memory, and it might get slower now that I'm accessing 2 fields instead of 1 `value` int(10), `half` bool, //or something similar to boolean What are your suggestions guys? Is the first option better, and what's the smallest data type in that case that would get me the 0.5?

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• Joining Tables Based on Foreign Keys

  - by maestrojed

  I have a table that has a lot of fields that are foreign keys referencing a related table. I am writing a script in PHP that will do the db queries. When I query this table for its data I need to know the values associated with these keys not the key. How do most people go about this? A 101 way to do this would be to query this table for its data including the foreign keys and then query the related tables to get each key's value. This could be a lot of queries (~10). Question 1: I think I could write 1 query with a bunch of joins. Would that be better? This approach also requires the querying script to know which table fields are foreign keys. Since I have many tables like this but all with different fields, this means writing nice generic functions is hard. MySQL InnoDB tables allow for foreign constraints. I know the database has these set up correctly. Question 2: What about the idea of querying the table and identifying what the constraints are and then matching them up using whatever process I decide on from Question 1. I like this idea but never see it being used in code. Makes me think its not a good idea for some reason. I would use something like SHOW CREATE TABLE tbl_name; to find what constraints/relationships exist for that table. Thank you for any suggestions or advice.

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• Help a CRUD programmer think about an "approval workflow"

  - by gerdemb

  I've been working on a web application that is basically a CRUD application (Create, Read, Update, Delete). Recently, I've started working on what I'm calling an "approval workflow". Basically, a request is generated for a material and then sent for approval to a manager. Depending on what is requested, different people need to approve the request or perhaps send it back to the requester for modification. The approvers need to keep track of what to approve what has been approved and the requesters need to see the status of their requests. As a "CRUD" developer, I'm having a hard-time wrapping my head around how to design this. What database tables should I have? How do I keep track of the state of the request? How should I notify users of actions that have happened to their requests? Is their a design pattern that could help me with this? Should I be drawing state-machines in my code? I think this is a generic programing question, but if it makes any difference I'm using Django with MySQL.

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