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  • About curse of dimensionality

    - by Dan
    My question is about this topic I've been reading about a bit. Basically my understanding is that in higher dimensions all points end up being very close to each other. The doubt I have is whether this means that calculating distances the usual way (euclidean for instance) is valid or not. If it were still valid, this would mean that when comparing vectors in high dimensions, the two most similar wouldn't differ much from a third one even when this third one could be completely unrelated. Is this correct? Then in this case, how would you be able to tell whether you have a match or not?

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  • What's the best way to test MSSQL connection programmatically?

    - by backslash17
    I need to develop a single routine that will be fired each 5 minutes to check if a list of MSSQL servers (10 to 12) are up and running. I can try to obtain a simple query in each one of the servers but this means that I have to create a table, view or stored procedure in every server, even if I use any already made SP I need to have a registered user in each server too. The servers are not in the same phisical location so having those requirements would be a complex task. Is there a way to simply "ping" from c# one MSSQL server? Thanks in advance!

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  • How to change data structure in mysql using mysqldump without deleting files

    - by Don Quixote
    Essentially what I'm trying to do is sync a production server with a sandbox server, but only the table structures and stored procedures. The procedures aren't any problem since they can be overriden, but the problem is the tables. I want to sync and alter their structures on the production server using mysqldump (or any other way that you can propose) without altering any existing data. If it helps, I only want to add more columns, not remove any existing ones. Also, I am using mysqlyog. Is there any way to do this?

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  • How to create unique user key

    - by Grayson Mitchell
    Scenario: I have a fairly generic table (Data), that has an identity column. The data in this table is grouped (lets say by city). The users need an identifier in order for printing on paper forms, etc. The users can only access their cites data, so if they use the identity column for this purpose they will see odd numbers (e.g. a 'New York' user might see 1,37,2028... as the listed keys. Idealy they would see 1,2,3... (or something similar) The problem of course is concurrency, this being a web application you can't just have something like: UserId = Select Count(*)+1 from Data Where City='New York' Has anyone come up with any cunning ways around this problem?

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  • How SqlDataAdapter works internally?

    - by tigrou
    I wonder how SqlDataAdapter works internally, especially when using UpdateCommand for updating a huge DataTable (since it's usually a lot faster that just sending sql statements from a loop). Here is some idea I have in mind : It creates a prepared sql statement (using SqlCommand.Prepare()) with CommandText filled and sql parameters initialized with correct sql types. Then, it loops on datarows that need to be updated, and for each record, it updates parameters values, and call SqlCommand.ExecuteNonQuery(). It creates a bunch of SqlCommand objects with everything filled inside (CommandText and sql parameters). Several SqlCommands at once are then batched to the server (depending of UpdateBatchSize). It uses some special, low level or undocumented sql driver instructions that allow to perform an update on several rows in a effecient way (rows to update would need to be provided using a special data format and a the same sql query (UpdateCommand here) would be executed against each of these rows).

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  • What will happen if I change the type of a column from int to year?

    - by MachinationX
    I have a table in MySQL 4.0 which currently has a year field as a smallint(6) type. What will happen if I convert it directly to a Year type with a query like the following: ALTER TABLE t MODIFY y YEAR(4) NOT NULL DEFAULT CURRENT_TIMESTAMP; When the current members of column y have values like 2010? I assume that because the year type is technically values from 1-255, values above that will be truncated or broken. So if MySQL isn't smart enough to realize that 2010(int) = 110(year), what would be the simplest query or queries to convert the values? Thanks for your help!

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  • how to get result from this data.

    - by Shantanu Gupta
    I want to compute result from this table. I want quantity 1 - quantity2 as another column in the table shown below. this table has more such records I am trying to query but not been able to get result. select * from v order by is_active desc, transaction_id desc PK_GUEST_ITEM_ID FK_GUEST_ID QUANTITY TRANSACTION_ID IS_ACTIVE ---------------- -------------------- ---------------------- -------------------- ----------- 12963 559 82000 795 1 12988 559 79000 794 0 12987 559 76000 793 0 12986 559 73000 792 0 12985 559 70000 791 0 12984 559 67000 790 0 12983 559 64000 789 0 12982 559 61000 788 0 12981 559 58000 787 0 12980 559 55000 786 0 12979 559 52000 785 0 12978 559 49000 784 0 12977 559 46000 783 0 12976 559 43000 782 0 I want another column that will contain the subtraction of two quantities . DESIRED RESULT SHOULD BE SOMETHING LIKE THIS PK_GUEST_ITEM_ID FK_GUEST_ID QUANTITY Result TRANSACTION_ID IS_ACTIVE ---------------- -------------------- ---------------------- -------------------- ----------- 12963 559 82000 3000 795 1 12988 559 79000 3000 794 0 12987 559 76000 3000 793 0 12986 559 73000 3000 792 0 12985 559 70000 3000 791 0 12984 559 67000 3000 790 0 12983 559 64000 3000 789 0 12982 559 61000 3000 788 0 12981 559 58000 3000 787 0 12980 559 55000 3000 786 0 12979 559 52000 3000 785 0 12978 559 49000 3000 784 0 12977 559 46000 3000 783 0 12976 559 43000 NULL 782 0

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  • DB optimization to use it as a queue

    - by anony
    We have a table called worktable which has some columns(key(primary key), ptime, aname, status, content) we have something called producer which puts in rows in this table and we have consumer which does an order-by on the key column and fetches the first row which has status as 'pending'. The consumer does some processing on this row: 1. updates status to "processing" 2. does some processing using content 3. deletes the row we are facing contention issues when we try to run multiple consumers(probably due to the order-by which does a full table scan)... using Advanced queues would be our next step but before we go there we want to check what is the max throughput we can achieve with multiple consumers and producer on the table. What are the optimizations we can do to get the best numbers possible? Can we do an in-memory processing where a consumer fetches 1000 rows at a time processes and deletes? will that improve? What are other possibilities? partitioning of table? parallelization? Index organized tables?...

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  • Question about Benchmark function in Mysql ( Incredible results ).

    - by xRobot
    I have 2 tables: author with 3 millions of rows. book with 20 miles rows. . So I have benchmarked this query with a join: SELECT BENCHMARK(100000000, 'SELECT book.title, author.name FROM `book` , `author` WHERE book.id = author.book_id ') And this is the result: Query took 0.7438 sec ONLY 0.7438 seconds for 100 millions of query with a join ??? Do I make some mistakes or this is the right result ?

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  • mysql query to get unique value from one column

    - by vesselyp
    i have a table named locations of which i want to select and get values in such a way that it should select only distinct values from a column but select all other values . table name: locations column names 1: country values : America, India, India, India column names 2: state/Province : Newyork, Punjab, Karnataka, kerala when i select i should get India only once and all the three states listed under India . is ther any way..??? sombody please help

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  • Difference between dates when grouping in SQL

    - by CeejeeB
    I have a table of purchases containing a user_id and a date_of_purchase. I need to be able to select all the users who have made 2 purchases within 12 months of each other. The dates can be any point in time as long as they are less than 12 months apart. e.g. user_id date_of_purchase 123 01/Jan/2010 124 01/Aug/2010 123 01/Feb/2010 124 05/Aug/2008 In this example i want user_id 123

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  • MSSQL Server using multiple ID Numbers

    - by vincer
    I have an web application that creates printable forms, these forms have a unique number on them, the problem is I have 2 forms that separate numbers need to be created for them. ie) Form1- Numbered 2000000-2999999 Form2- Numbered 3000000-3999999 dbo.test2 - is my form information table Tsel - is my autoinc table for the 3000000 series numbers Tadv - is my autoinc table for the 2000000 series numbers What I have done is create 2 tables with just autoinc row (one for 2000000 series numbers and one for 3000000 series numbers), I then created a trigger to add a record to the coresponding table, read back the autoinc number and add it to my table that stores the form information including the just created autoinc number for the right series of forms. Although it does work, I'm concerned that the numbers will get messed up under load. I'm not sure the @@IDENTITY will always return the right value when many people are using the system. (I cannot have duplicates and I need to use the numbering form show above. Thanks for any help See code below. ** TRIGGER ** CREATE TRIGGER MAKEANID2 ON dbo.test2 AFTER INSERT AS SET NOCOUNT ON declare @someid int declare @someid2 int declare @startfrom int declare @test1 varchar(10) select @someid=@@IDENTITY select @test1 = (Select name1 from test2 where sysid = @someid ) if @test1 = 'select' begin insert into Tsel Default values select @someid2 = @@IDENTITY end if @test1 = 'adv' begin insert into Tadv Default values select @someid2 = @@IDENTITY end update test2 set name2=(@someid2) where sysid = @someid SET NOCOUNT OFF

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  • Money type field returns Dollar, but regional set to UK (Windows 7)

    - by Gareth
    Hi, On a Windows 7 machine with Advantage Data Architect version 9.10.0.11, money type data is returned as Dollars, instead of Pounds. Sometimes, it will suddenly switch to Pounds, without me changing any settings. Everything else returns Pounds correctly (regional settings is UK with £ as the currency symbol). Has anyone else had this problem and/or found a solution? If I run any reports using the money data type field I can't be sure that it's going to be accurate. And no, I can't change the field type and handle the currency symbol myself. Any help would be appreciated.

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  • MySQL query problem

    - by Luke
    Ok, I have the following problem. I have two InnoDB tables: 'places' and 'events'. One place can have many events, but event can be created without entering place. In this case event's foreign key is NULL. Simplified structure of the tables looks as follows: CREATE TABLE IF NOT EXISTS `events` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, `places_id` int(9) unsigned DEFAULT NULL, PRIMARY KEY (`id`), KEY `fk_events_places` (`places_id`), ) ENGINE=InnoDB; ALTER TABLE `events` ADD CONSTRAINT `events_ibfk_1` FOREIGN KEY (`places_id`) REFERENCES `places` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION; CREATE TABLE IF NOT EXISTS `places` ( `id` int(9) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) COLLATE utf8_bin NOT NULL, PRIMARY KEY (`id`), ) ENGINE=InnoDB; Question is, how to construct query which contains name of the event and name of the corresponding place (or no value, in case there is no place assigned?). I am able to do it with two queries, but then I am visibly separating events which have place assigned from the ones that are without place. Help really appreciated.

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  • db optimization - have a total field or query table?

    - by Dorian Fife
    I have an app where users get points for actions they perform - either 1 point for an easy action or 2 for a difficult one. I wish to display to the user the total number of points he got in my app and the points obtained this week (since Monday at midnight). I have a table that records all actions, along with their time and number of points. I have two alternatives and I'm not sure which is better: Every time the user sees the report perform a query and sum the points the user got Add two fields to each user that records the number of points obtained so far (total and weekly). The weekly points value will be set to 0 every Monday at midnight. The first option is easier, but I'm afraid that as I'll get many users and actions queries will take a long time. The second option bares the risk of inconsistency between the table of actions and the summary values. I'm very interested in what you think is the best alternative here. Thanks, Dorian

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  • Solr admin with only JRE possible?

    - by Camran
    I have installed JRE on my Ubuntu server. However, not JDK. When I execute solr to start, everything seems fine. But I cant access the solr/admin page. Wonder if this is possible without the JDK? Or do I have to have JDK installed? Thanks

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  • PhpMyAdmin; Should I disable root login?

    - by Camran
    I have this setup in Phpmyadmin: USER HOST PASSW PRIVILEGES GRANT debian-sys-maint localhost Yes ALL PRIVILEGES YES phpmyadmin localhost Yes USAGE NO root 127.0.0.1 Yes ALL PRIVILEGES YES root localhost Yes ALL PRIVILEGES YES root my_hostname Yes ALL PRIVILEGES YES username localhost Yes ALL PRIVILEGES YES Where "username" is my username and "my_hostname" is my hostname. I am currently only logging in as the last one (username, localhost). Also, I have php which also uses the last ones login details. Should I disable the other ones? And, what other security measures should I take? BTW: My server is Linux and I have root access. Thanks

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  • Conditional PIVOT/transform problem

    - by IanC
    Hi folks I have a table with three columns, which we'll call ID1, ID2, and Value. Sample data: ID ID1 Value 1 1 0 1 2 1 1 3 1 1 3 2 1 4 0 1 4 1 1 5 0 1 5 2 2 1 2 Value is limited to 0, 1, or 2. What I need to do is pivot/transform this data into a column-based count of how many times each possible Value appears, grouped by ID, ID1. The output of the above should be: ID ID1 Val0 Val1 Val2 1 1 1 0 0 1 2 0 2 0 1 3 0 1 1 1 4 1 1 0 1 5 1 0 1 2 1 0 0 1 I'm using SQL Server 2008. How do I do this?

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  • FKs on all tables for status colunm

    - by Jonarch
    I have a colunm "Status" in every table in my DB. The purpose of it is to show if the given row is in use or if it has been deactivated. So values can be (0=deactive and 1= active). Two ways I see this: I can have enums or I am thinking if it is better to keep this colunm as a FK which references the main system data dictionary table which has all the codes used on the system. (website) The benefit is every table, every row can then be centralized through this FK. So if i ever want to check all rows which are deactive on my system i can from this table as all th child tables will have like status = ID 233, where 233 = deactive in the data dictionary table. Any benefit or should i stick with the old way of enums?. Also I am thinking if i need one more status for deleted or is that same as deactivated?

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  • Has inheritance become bad?

    - by mafutrct
    Personally, I think inheritance is a great tool, that, when applied reasonably, can greatly simplify code. However, I seems to me that many modern tools dislike inheritance. Let's take a simple example: Serialize a class to XML. As soon as inheritance is involved, this can easily turn into a mess. Especially if you're trying to serialize a derived class using the base class serializer. Sure, we can work around that. Something like a KnownType attribute and stuff. Besides being an itch in your code that you have to remember to update every time you add a derived class, that fails, too, if you receive a class from outside your scope that was not known at compile time. (Okay, in some cases you can still work around that, for instance using the NetDataContract serializer in .NET. Surely a certain advancement.) In any case, the basic principle still exists: Serialization and inheritance don't mix well. Considering the huge list of programming strategies that became possible and even common in the past decade, I feel tempted to say that inheritance should be avoided in areas that relate to serialization (in particular remoting and databases). Does that make sense? Or am messing things up? How do you handle inheritance and serialization?

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