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  • Best Embedded SQL DB for write performance?

    - by max.minimus
    Has anybody done any benchmarking/evaluation of the popular open-source embedded SQL DBs for performance, particularly write performance? I've some 1:1 comparisons for sqlite, Firebird Embedded, Derby and HSQLDB (others I am missing?) but no across the board comparisons... Also, I'd be interested in the overall developer experience for any of these (for a Java app).

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  • Easiest solution to sync an offline (local desktop application) database with a central server and multiple pc's?

    - by tyfius
    I have a desktop application which uses a local database. (This can be SQLite, SqlCe, PostgreSQL or any other database I will be able to install locally, I haven't decided which one to use yet.) The plan is to achieve the following: A user can subscribe to some kind of cloud service. If he does his local database should be synced with the online database (one for all users, or one per user, whatever the easiest solution is) so he will be able to sync his local database data between multiple PC's, can access his data online. (Much like dropbox does for files.) What is the best, easiest (and preferably cheapest) solution to achieve this? I am looking into DataObjects.net but I can't find much documentation about their Sync feature. Or, are there other alternatives? For example, I start with some kind of cloud service which allows local caching and use the local caching for users who do not subscribe to the service. Any pointers, tips or experiences are welcome.

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  • how to store data with many categories and many properties efficiently?

    - by Mickey Shine
    We have a large number of data in many categories with many properties, e.g. category 1: Book properties: BookID, BookName, BookType, BookAuthor, BookPrice category 2: Fruit properties: FruitID, FruitName, FruitShape, FruitColor, FruitPrice We have many categories like book and fruit. Obviously we can create many tables for them (MySQL e.g.), and each category a table. But this will have to create too many tables and we have to write many "adapters" to unify manipulating data. The difficulties are: 1) Every category has different properties and this results in a different data structure. 2) The properties of every categoriy may have to be changed at anytime. 3) Hard to manipulate data if each category a table (too many tables) How do you store such kind of data?

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  • Read and write .NET Objects in SQL Database without serialization.

    - by Mohit
    Hello, I have a small query. I need to create a Caching Service of my own that will write and read .NET Objects to and from the Database. Now, I have achieved that with the help of Binary Serialization. But the Problem is I need to deliberately marked my objects as [Serializable], which makes me think that what if someone will try to add an object which is not marked as [Serializable]. Thus, I need to find a way to read and write Objects to Database without Serialization. I have one thought too.. As we all know Session can store any object in it. Now, we can make sessions to be stored in the DB, outproc. What mechanism it uses to store these objects without serializing or deserializing. Any help will be highly appreciated. Thanks. M.B

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  • JQuery selectors select from an html object other than from document root?

    - by orangebrainer
    jQuery selectors select from the document. How do I select from somewhere else other than root? Say I want to select some children from an html object. For this function dothis(obj) { $j("#tabs").removeClass(); $j("#tabs>ul").removeClass(); $j("#tabs>ul>li>a").each(function() { var tabNum = $j(this).attr("href").replace("#", ""); var tabContent = $j("div[id=" + tabNum + "]"); tabContent.removeClass(); $(tabContent).before("<br><h1>" +$j(this).text() + "</h1>\n" ); }); $j("#tabs>ul").each(function() { $j(this).empty();//remove Ul links on top }); } I want to reference the selectors from an html Object (obj) i passed into as argument, instead of selecting from document. Sorry I'm pretty new to jQuery.

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  • Running a sharded DB from a single machine

    - by ming yeow
    This sounds kinda dumb, but I have a sharded DB that I no longer think I need to run on 2 machines, and would like to run on one single machine instead. Any ideas on how that can potentially be done? There are lots of resources on how i can achieve the converse, but very little on how this can be done

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  • Foreign keys and NULL in mySQL

    - by Industrial
    Hi everyone, Can I have a column in my values table (value) referenced as a foreign key to knownValues table, and let it be NULL whenever needed, like in the example: Table: values product type value freevalue 0 1 NULL 100 1 2 NULL 25 3 3 1 NULL Table: types id name prefix 0 length cm 1 weight kg 2 fruit NULL Table: knownValues id Type name 0 2 banana Note: The types in the table values & knownValues are of course referenced into the types table. Thanks!

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  • What's the best way to store custom objects in relational database?

    - by user342610
    I have my objects with their properties. Objects could change their structure: properties may be added/removed/changed. Objects could be absolutely dropped. So object's metadata (description, classes, call them like you want :) )could be changed. The database should store objects schemas and instances of these objects. What's the best way to organise a relational database structure to store data mentioned above? Currently I see only two ways: 1) Store objects schemas in a few tables: schema general data,schema properties, possible properties types. Store instances in their tables: instance general data, a few tables - per each type from possible properties types table to store instance properties data. And so on. 2) store objects schemas like in p1 but store instances like XML files in one table: one table for general instance info and one table with instance XML. please, don't ask why/for what I need this. Just need to store custom objects and DB should work fast :)

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  • One on One table relation - is it harmful to keep relation in both tables?

    - by EBAGHAKI
    I have 2 tables that their rows have one on one relation.. For you to understand the situation, suppose there is one table with user informations and there is another table that contains a very specific informations and each user can only link to one these specific kind of informations ( suppose second table as characters ) And that character can only assign to the user who grabs it, Is it against the rules of designing clean databases to hold the relation key in both tables? User Table: user_id, name, age, character_id Character Table: character_id, shape, user_id I have to do it for performance, how do you think about it?

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  • delete rows using sql 'like' command using data from another table

    - by Captastic
    Hi All, I am trying to delete rows from a table ("lovalarm") where a field ("pointid") is like any one of a number of strings. Currently I am entering them all manually however I need to be able to have a list of over 100,000 options. My thoughts are to have a table ("lovdata") containing all possible strings and running a query to delete rows where the field is 'like' any of the strings in the other table. Can anyone point me in the right direction as to if/how I can use like in this way? Many thanks, Cap

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  • is Payment table needed when you have an invoice table like this?

    - by EBAGHAKI
    this is my invoice table: Invoice Table: invoice_id creation_date due_date payment_date status enum('not paid','paid','expired') user_id total_price I wonder if it's Useful to have a payment table in order to record user payments for invoices. payment table can be like this: payment_id payment_date invoice_id price_paid status enum('successful', 'not successful')

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  • Do Java or C++ lack any OO features?

    - by tsv
    I am interested in understanding object-oriented programming in a more academic and abstract way than I currently do, and want to know if there are any object-oriented concepts Java and C++ fail to implement. I realise neither of the languages are "pure" OO, but I am interested in what (if anything) they lack, not what they have extra.

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  • Speeding up a group by date query on a big table in postgres

    - by zaius
    I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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  • IntegrityError with Booleand Fields and Postgresql

    - by xRobot
    I have this simple Blog model: class Blog(models.Model): title = models.CharField(_('title'), max_length=60, blank=True, null=True) body = models.TextField(_('body')) user = models.ForeignKey(User) is_public = models.BooleanField(_('is public'), default = True) When I insert a blog in admin interface, I get this error: IntegrityError at /admin/blogs/blog/add/ null value in column "is_public" violates not-null constraint Why ???

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  • How do I sync a subset of tables between two databases on the same mysql database server

    - by Mike
    would like to be able to sync a subset of tables between two mysql databases that are running on the same server. One of the databases acts as the master where inserts, updates and deletes can be made. The second database uses those same tables for read-only operations. I do not want to use federated tables to achieve this. The long term goal will be to separate the 2 databases to multiple servers, The second database that has the subset of tables as read-only may also be replicated a few times over to distribute geographically for load and performance purposes each with unqiue data.... Once that is achieved, I plan to use binlog to replicate those specific tables on the secondary databases. In the meantime, I'd like to keep these tables in sync. Is there a more elegant way to do this than other than using a cronjob and mysqldump?

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  • What does ON [PRIMARY] mean?

    - by Icono123
    I'm creating an SQL setup script and I'm using someone else's script as an example. Here's an example of the script: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[be_Categories]( [CategoryID] [uniqueidentifier] ROWGUIDCOL NOT NULL CONSTRAINT [DF_be_Categories_CategoryID] DEFAULT (newid()), [CategoryName] [nvarchar](50) NULL, [Description] [nvarchar](200) NULL, [ParentID] [uniqueidentifier] NULL, CONSTRAINT [PK_be_Categories] PRIMARY KEY CLUSTERED ( [CategoryID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO Does anyone know what the ON [PRIMARY] command does? Regards.

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  • What is the proper design of storing temporary users? [closed]

    - by Mendy
    In SO site both real users and temporary users can add a new questions. I assume each user type has a different table. My question is how can I attach the question to the right user? I assuming the temp users have their own table from the following reasons: Temp users don't have all the data that real users have. like: email, password, and all users details. On the other hand, temp users are a lot more then real users. So it make more sense to have they in their own table.

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  • replicating master tables mapping in transaction tables

    - by NoDisplay
    I have three master tables for location information Country {ID, Name} State {ID, Name, CountryID} City {ID, Name, StateID} Now I have one transcation table called Person which hold the person name and his location information. My Question is shall I have only CityID in the Person table like this: Person {ID, Name, CityID}' And have view of join query which give me detail like "Person{ID,Name,City,State,Country}" or Shall I replicate the mapping Person {ID, Name, CityID, StateID, CountryID} Please suggest which do you feel is to be selected and why? if there is any other option available, please suggest. Thanks in advance.

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  • which sql query is more efficient: select count(*) or select ... where key>value?

    - by davka
    I need to periodically update a local cache with new additions to some DB table. The table rows contain an auto-increment sequential number (SN) field. The cache keeps this number too, so basically I just need to fetch all rows with SN larger than the highest I already have. SELECT * FROM table where SN > <max_cached_SN> However, the majority of the attempts will bring no data (I just need to make sure that I have an absolutely up-to-date local copy). So I wander if this will be more efficient: count = SELECT count(*) from table; if (count > <cache_size>) // fetch new rows as above I suppose that selecting by an indexed numeric field is quite efficient, so I wander whether using count has benefit. On the other hand, this test/update will be done quite frequently and by many clients, so there is a motivation to optimize it.

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