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  • What data is actually stored in a B-tree database in CouchDB?

    - by Andrey Vlasovskikh
    I'm wondering what is actually stored in a CouchDB database B-tree? The CouchDB: The Definitive Guide tells that a database B-tree is used for append-only operations and that a database is stored in a single B-tree (besides per-view B-trees). So I guess the data items that are appended to the database file are revisions of documents, not the whole documents: +---------|### ... | | +------|###|------+ ... ---+ | | | | +------+ +------+ +------+ +------+ | doc1 | | doc2 | | doc1 | ... | doc1 | | rev1 | | rev1 | | rev2 | | rev7 | +------+ +------+ +------+ +------+ Is it true? If it is true, then how the current revision of a document is determined based on such a B-tree? Doesn't it mean, that CouchDB needs a separate "view" database for indexing current revisions of documents to preserve O(log n) access? Wouldn't it lead to race conditions while building such an index? (as far as I know, CouchDB uses no write locks).

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  • Copy VSS structure to server with asp.net

    - by Tyzak
    i want to copy the structure (with the documents) from our vss server to an webserver. Therefore i want to create an application which is on this webserver. i want to use asp.net. i don't know what exactly i need therefore : I have to build somekind of connection? then go throw the structure and copy it somehow : ? important: i want to copy the documents with the right creation date ( it changes when i just copy the doc.) are there APIs for asp.net <- vss?

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  • Syntax Error with MySQL 5.1 Server

    - by Mr.Z
    I am trying to connect to a server remotely using the command line client window. I am using MySQL 5.1 and I do not know why I am getting syntax error. If you can help me, that would be much appreciated. username as user password as pass hostname as example.com I have tried: mysql> -u user -h example.com -p ; mysql> -h example.com -u user -p ; I have looked at the reference manual and other verisons of remote connection with Server 5.1 but I can't see the syntax error.

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  • How to find date ranges in records with consecutive dates and duplicate data

    - by alan s
    There's probably any easy solution for this, but I can't see it. I have a table with consecutive dates and often duplicate associated data for several of these consecutive dates: Date Col1 Col2 5/13/2010 1 A 5/14/2010 1 A 5/15/2010 2 B 5/16/2010 1 A 5/17/2010 1 A 5/18/2010 3 C 5/19/2010 3 C 5/20/2010 3 C Using MS T-SQL, I wish to find the start and end dates for each run of distinct Col1 and Col2 values: StartDate EndDate Col1 Col2 5/13/2010 5/14/2010 1 A 5/15/2010 5/15/2010 2 B 5/16/2010 5/17/2010 1 A 5/18/2010 5/20/2010 3 C Assumptions: There are never any missing dates. Col1 and Col2 are not null. Any ideas - preferably that don't use cursors? Many thanks, -alan

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  • Prroblem with ObjectDelete() in Entity Framework 4

    - by Tom
    I got two entities: public class User : Entity { public virtual string Username { get; set; } public virtual string Email { get; set; } public virtual string PasswordHash { get; set; } public virtual List<Photo> Photos { get; set; } } and public class Photo : Entity { public virtual string FileName { get; set; } public virtual string Thumbnail { get; set; } public virtual string Description { get; set; } public virtual int UserId { get; set; } public virtual User User { get; set; } } When I try to delete the photo it works fine for the DB (record gets romoved from the table) but it doesnt for the Photos collection in the User entity (I can still see that photo in user.Photos). This is my code. What I'm doing wrong here? Changing entity properties works fine. When I change photo FileName for example it gets updated in DB and in user.Photos. var photo = SelectById(id); Context.DeleteObject(photo); Context.SaveChanges(); var user = GetUser(userName); // the photo I have just deleted is still in user.Photos also tried this but getting same results: var photo = user.Photos.First(); Context.DeleteObject(photo); Context.SaveChanges();

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  • Explain this SQL query in plain English.

    - by Kevinniceguy
    Please explain, in plain English, what question this SQL query answers: SELECT SUM(price) FROM Room r, Hotel h WHERE r.hotelNo = h.hotelNo and hotelName = 'Paris Hilton' and roomNo NOT IN (SELECT roomNo FROM Booking b, Hotel h WHERE (dateFrom <= CURRENT_DATE AND dateTo >= CURRENT_DATE) AND b.hotelNo = h.hotelNo AND hotelName = 'Paris Hilton');

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  • Setting 0/1-to-1 relationship in SQLAlchemy?

    - by Timmy
    is there a proper way of setting up a 0/1-to-1 relationship? i want to be able to check if the related item exists without creating it: if item.relationship is None: item.relationship = item2() but it creates the insert statements on the if statement

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  • How to make Django work with unsupported MySQL drivers such as gevent-mysql or Concurrence's MySQL d

    - by Continuation
    I'm interested in running Django on an async framework like Concurrence or gevent. Both frameworks come with its own async MySQL driver. Problem is Django only officially supports MySQLdb. What do I need to do to make Django work with the MySQL drivers that come with gevent or Concurrence? Is there a step-by-step guide somewhere that I can follow? Is this a major undertaking? Thanks.

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  • True or False: Good design calls for every table to have a primary key, if nothing else, a running i

    - by Velika
    Consider a grocery store scenario (I'm making this up) where you have FACT records that represent a sale transaction, where the columns of the Fact table include SaleItemFact Table ------------------ CustomerID ProductID Price DistributorID DateOfSale Etc Etc Etc Even if there are duplicates in the table when you consider ALL the keys, I would contend that a surrogate running numeric key (i.e. identity column) should be made up, e.g., TransactionNumber of type Integer. I can see someone arguing that a Fact table might not have a unique key (though I'd invent one and waste the 4 bytes, but how about a dimension table?

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  • why is there extra using where in execution plan of query

    - by user366534
    I see plan of query: EXPLAIN SELECT * FROM `subscribers` WHERE state =4 AND date_added < '2010-12-23 11:47:45' It shows: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE subscribers range state_date_added state_date_added 9 NULL 8 Using where Here is indexes of table: Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment subscribers 0 PRIMARY 1 subscriber_id A 382039 NULL NULL BTREE subscribers 0 email_list_id 1 email_address A 191019 NULL NULL BTREE subscribers 0 email_list_id 2 list_id A 382039 NULL NULL BTREE subscribers 1 FK_list_id 1 list_id A 10 NULL NULL BTREE subscribers 1 state_date_added 1 state A 12 NULL NULL BTREE subscribers 1 state_date_added 2 date_added A 8128 NULL NULL BTREE The last two lines describes index what is supposed for the query. Why is there in extra column using where? Even If I fetch only state and date_added column, it has in extra column: Using where; Using index. I understand why it has using index, but I don't understand Using where here.

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  • Mysql random rows

    - by n00b
    please read the whole question... 90% of you dont seem to do that and some of you only read the title obviously... and if you dont know the solution, dont answer - i wont have to downvote you -.-'' im entertaining the idea of getting random rows directly from mysql. what i found was SELECT * FROM tablename WHERE somefield='something' ORDER BY RAND() LIMIT 5 but even i see how slow that would be.. is the only way to do this doing something like SELECT * FROM tablename WHERE somefield='something' LIMIT RAND(aincrementvalue-5), 1 5 times? or is there a way that i with my little knowlege of databases cant come up with ? (no i dont want random indexes. i hate the idea of them...) @commenters - please first look, then think, then look again, think again and then post. i wont point fingers but i dislike stupid comments and why i think random indexes are a nasty hack ? it doesnt give you random results. it gives you x results from a random index in a predefined order its like a gapless id only in the wrong order if you fetch by 1 row and get true randomness you fall back to my method but with an additional junk field finally the reason the field exists is only to serve as a helper to something that can be done without it with almost same performance (but the quality (randomness) is better), so it is a nasty hack ;) i solved it, look @ my answer... if you think its incorrect please tell me :)

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  • Adding Postgres table cells based on same value

    - by russell kinch
    I have a table called expenses. There are numerous columns but the ones involved in my php page are date, spplierinv, amount. I have created a page that lists all the expenses in a given month and totals it at the end. However, each row has a value, but many rows might be on the same supplier invoice.This means adding each row with the same supplierinv to get a total as per my bank statement. Is there anyway I can get a total for the rows based on the supplierinv. I mean say I have 10 rows. 5 on supplierinv 4, two on supplierinv 5 and 3 on supplierinv 12, how can a get 3 figures (inv 4, 5 and 12) and the grand total at the bottom. Many thanks

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  • How to efficiently store and update binary data in Mongodb?

    - by Rocketman
    I am storing a large binary array within a document. I wish to continually add bytes to this array and sometimes change the value of existing bytes. I was looking for some $append_bytes and $replace_bytes type of modifiers but it appears that the best I can do is $push for arrays. It seems like this would be doable by performing seek-write type operations if I had access somehow to the underlying bson on disk, but it does not appear to me that there is anyway to do this in mongodb (and probably for good reason). If I were instead to just query this binary array, edit or add to it, and then update the document by rewriting the entire field, how costly will this be? Each binary array will be on the order of 1-2MB, and updates occur once every 5 minutes and across 1000s of documents. Worse, yet there is no easy way to spread these out (in time) and they will usually be happening close to one another on the 5 minute intervals. Does anyone have a good feel for how disastrous this will be? Seems like it would be problematic. An alternative would be to store this binary data as separate files on disk, implement a thread pool to efficiently manipulate the files on disk, and reference the filename from my mongodb document. (I'm using python and pymongo so I was looking at pytables). I'd prefer to avoid this though if possible. Is there any other alternative that I am overlooking here? Thanks in advnace.

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  • Query two tables from different schema

    - by Guru
    Hi- I have two different schemas in Oracle (say S1, S2). And two tables in those schemas(say S1.Table1, S2.Table2). I want to query these two tables from schema S1. Both S1 and S2 are in different databases. From DB1 - Schema S1, I want to do something like this, select T1.Id from S1.Table1 T1 , S2.Table2 T2 Where T1.Id = T2.refId I know one way of doing this would be creating a DB Link for the second schema and use it in querying. But sadly, I don't have priv to create DB link. Is there some way to do without DB link, like, in TOAD, you can compare two schema objects. But again, two schema objects and it is general comparision. Not like querying them. Any ideas, suggestions are greatly appriciated. Thanks in advance.

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  • explain these select statements!

    - by user329820
    Hi, I can not get the difference betwwn these statements? would you please help me,I have read some sample of select statements but I did not get these ones. SELECT 'B' FROM T WHERE A = (SELECT NULL); SELECT 'C' FROM T WHERE A = ANY (SELECT NULL); SELECT 'D' FROM T WHERE A = A; I use MySQL

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  • Composite Primary and Cardinality

    - by srini.venigalla
    I have some questions on Composite Primary Keys and the cardinality of the columns. I searched the web, but did not find any definitive answer, so I am trying again. The questions are: Context: Large (50M - 500M rows) OLAP Prep tables, not NOSQL, not Columnar. MySQL and DB2 1) Does the order of keys in a PK matter? 2) If the cardinality of the columns varies heavily, which should be used first. For example, if I have CLIENT/CAMPAIGN/PROGRAM where CLIENT is highly cardinal, CAMPAIGN is moderate, PROGRAM is almost like a bitmap index, what order is the best? 3) What order is the best for Join, if there is a Where clause and when there is no Where Clause (for views) Thanks in advance.

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  • mysql: storing arbitrary data

    - by Hailwood
    Background: I was asking a question on stack overflow regarding creating tables on the fly where this conversation ensued: This smells like a terrible idea! In fact, it smells just like this one. What in the world do you want to use this for? – deceze @deceze: very true, However, How else would you store the contents of these CSV files. They must be stored in mysql for indexing. The only solid fact about them is that they all have a mobile column with a standard format. The CSV can have an arbitrary amount of columns with an arbitrary amount of rows. They can (with no exaggeration) range from a single row, 35 column csv to an 80k row single column CSV. I am open to other ideas. – Hailwood There are many solutions for this, from attribute-value schemas to JSON storage and NoSQL storage. Open a new question about it. Whatever you do though, don't dynamically create tables! – deceze Question: So my question is, What would you say is the best way to store this data? Are you in agreement with deceze about not creating dynamic tables?

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  • has anyone produced an in-memory GIT repository?

    - by Andrew Matthews
    I would like to be able to take advantage of the benefits of GIT (and its workflows), but without the cost of disk access - I just would like to leverage the distributed revision control capabilities of GIT to produce something like a hybrid of memcached and GIT. (preferably in .NET) Is there such a beast out there?

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