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• Why are joins bad when considering scalability?

  - by acidzombie24

  Why are joins bad or 'slow'. I know i heard this more then once. I found this quote The problem is joins are relatively slow, especially over very large data sets, and if they are slow your website is slow. It takes a long time to get all those separate bits of information off disk and put them all together again. source I always thought they were fast especially when looking up a PK. Why are they 'slow'?

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• Advanced queries in HBase

  - by Teflon Ted

  Given the following HBase schema scenario (from the official FAQ)... How would you design an Hbase table for many-to-many association between two entities, for example Student and Course? I would define two tables: Student: student id student data (name, address, ...) courses (use course ids as column qualifiers here) Course: course id course data (name, syllabus, ...) students (use student ids as column qualifiers here) This schema gives you fast access to the queries, show all classes for a student (student table, courses family), or all students for a class (courses table, students family). How would you satisfy the request: "Give me all the students that share at least two courses in common"? Can you build a "query" in HBase that will return that set, or do you have to retrieve all the pertinent data and crunch it yourself in code?

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• error in arabic script in mysql

  - by fusion

  i inserted data in mysql database which includes arabic script. while the output displays arabic correctly, the data in mysql looks like garbage. something like this: '&#1589;&#1614;&#1608;&#1605;&#1615; &#1579;&#1614;&#1604;&#1575;&#1579;&#1614;&#1577;&#1616; &#1571;&#1610;&#1617;&#1575;&#1605;&#1613; &#1605;&#1616;&#1606; &#1603;&#1615;&#1604;&#1617;&#1616; &#1588;&#1614;&#1607;&#1585;&#1613; &#1600; &#1571;&#1585;&#1576;&#1614;&#1593;&#1575;&#1569;&#1615; &#1576;&#1614;&#1610;&#1606;&#1614; &#1582;&#1614; should i be worried about this? if yes, how do i make it appear in proper arabic script in mysql? thanks.

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• Converting time/date from XML file into MYSQL format

  - by IconicDigital

  One of the affiliate networks provides a feed with the following time/date format. <startDate>1349992800000</startDate> <endDate>1355266799999</endDate> My problem is I am trying to convert this to a MYSQL format, I have tried mktime and strtotime with no luck the date seems to come out wrong. I know this is the time since the Equinox, I am just not sure how to convert this to a MYSQL format.

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• Why is doing a top(1) on an indexed column in mssql slow?

  - by reinier

  I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work?

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• Circular database relationships. Good, Bad, Exceptions?

  - by jim

  I have been putting off developing this part of my app for sometime purely because I want to do this in a circular way but get the feeling its a bad idea from what I remember my lecturers telling me back in school. I have a design for an order system, ignoring the everything that doesn't pertain to this example I'm left with: CreditCard Customer Order I want it so that, Customers can have credit cards (0-n) Customers have orders (1-n) Orders have one customer(1-1) Orders have one credit card(1-1) Credit cards can have one customer(1-1) (unique ids so we can ignore uniqueness of cc number, husband/wife may share cc instances ect) Basically the last part is where the issue shows up, sometimes credit cards are declined and they wish to use a different one, this needs to update which their 'current' card is but this can only change the current card used for that order, not the other orders the customer may have on disk. Effectively this creates a circular design between the three tables. Possible solutions: Either Create the circular design, give references: cc ref to order, customer ref to cc customer ref to order or customer ref to cc customer ref to order create new table that references all three table ids and put unique on the order so that only one cc may be current to that order at any time Essentially both model the same design but translate differently, I am liking the latter option best at this point in time because it seems less circular and more central. (If that even makes sense) My questions are, What if any are the pros and cons of each? What is the pitfalls of circular relationships/dependancies? Is this a valid exception to the rule? Is there any reason I should pick the former over the latter? Thanks and let me know if there is anything you need clarified/explained. --Update/Edit-- I have noticed an error in the requirements I stated. Basically dropped the ball when trying to simplify things for SO. There is another table there for Payments which adds another layer. The catch, Orders can have multiple payments, with the possibility of using different credit cards. (if you really want to know even other forms of payment). Stating this here because I think the underlying issue is still the same and this only really adds another layer of complexity.

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• Temporary intermediate table

  - by user289429

  In our project to generate massive reports in oracle we use some permanent table to hold intermediate results. For example to generate one report we run few queries and populate the table, at the final step we join the intermediate table with huge application tables. These intermediate tables are cleared for next report run. We have few concerns in performance areas. These intermediate tables are transactional and don't have statistics. Is it good idea to join these with application tables which are partitioned and have up to date statistics. We need these results stored in the intermediate tables to be available across requests from UI hence we are not in a position to use oracle provided temporary tables. Any thoughts on what could be done would be appreciated.

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• Selecting records with specific month and year in SQL Server 2005

  - by John

  I want to list records with a particular month and year. The table name is 'Arrival' and 'date' is the field that stores the date that the record was added. This is to be done from a C# application. For example, if the user selects month as 'April' and year as '2009' in the application, it will list all the records that were added on April,2009. (I only need the query, hope I can figure out the rest :) )

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• Arranging VS2008 generated LinqToSql/EntityFramework data models/contexts in assemblies.

  - by JMSA

  What pattern should I use for data-access in case of VS2008 generated L2s or EF DataModels? Repository-pattern or what? As we know VS2008 generates Data-Models and DataContexts/ObjectContexts in the same file, then, how should I arrange my VS2008 assemblies in my VS2008 solution to achieve a layered design? If I use repository pattern, how should I arrange my assemblies in the VS2008 solution (as Data-Models and Data/Object-Contexts are stored in the same file...)? Any web/example link would be appreciated.

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• Find Date From Non Contiguous Ranges

  - by AGoodDisplayName

  I am looking to find an best way to find a date from date ranges that may or may not be contiguous (I am trying to avoid a cursor, or a heavy function if possible). Lets say I have hotel guests that come and go (check in, check out). I want to find the date that a certain guest stayed their 45th night with us. The database we use records the data as so: Create Table #GuestLog( ClientId int, StartDate DateTime, EndDate DateTime) Here is some data Insert Into #GuestLog Values(1, '01/01/2010', '01/10/2010') Insert Into #GuestLog Values(1, '01/16/2010', '01/29/2010') Insert Into #GuestLog Values(1, '02/13/2010', '02/26/2010') Insert Into #GuestLog Values(1, '04/05/2010', '06/01/2010') Insert Into #GuestLog Values(1, '07/01/2010', '07/21/2010') So far I can only think of solutions that involve functions with temp tables and crazy stuff like that, I feel like I'm over thinking it. Thanks ahead of time.

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• Java Prepared Statement Error

  - by Suresh S

  Hi Guys the following code throws me an error i have an insert statement created once and in the while loop i am dynamically setting parameter , and at the end i says ps2.addBatch() again while ( (eachLine = in.readLine()) != null)) { for (int k=stat; k <=45;k++) { ps2.setString (k,main[(k-2)]); } stat=45; for (int l=1;l<= 2; l++) { ps2.setString((stat+l),pdp[(l-1)]);// Exception } ps2.addBatch(); } This is the error java.lang.ArrayIndexOutOfBoundsException: 45 at oracle.jdbc.dbaccess.DBDataSetImpl._getDBItem(DBDataSetImpl.java:378) at oracle.jdbc.dbaccess.DBDataSetImpl._createOrGetDBItem(DBDataSetImpl.java:781) at oracle.jdbc.dbaccess.DBDataSetImpl.setBytesBindItem(DBDataSetImpl.java:2450) at oracle.jdbc.driver.OraclePreparedStatement.setItem(OraclePreparedStatement.java:1155) at oracle.jdbc.driver.OraclePreparedStatement.setString(OraclePreparedStatement.java:1572) at Processor.main(Processor.java:233)

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• Should searchable date fields in a database table always be indexed?

  - by Spencer Ruport

  If I have a field in a table of some date type and I know that I will always be searching it using comparisons like between, > or < and never = could there be a good reason not to add an index for it?

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• Right way to implement a n-to-m related

  - by ThreeFingerMark

  Hello, this is a part from my database structure: Table: Item Columns: ItemID, Title, Content, Price Table: Tag Columns: TagID, Title Table: ItemTag Columns: ItemID, TagID Table: Image Columns: ImageID, Path, Size, UploadDate Table: ItemImage Columns: ItemID, ImageID The items can have more than one image so i have a extra table "Image" and map this images to an items. I see now a problem with this structure. Before i can add Images i must enter an item. My question is now. Is this structure a good way to solve my problem with many images / tags for one item? Thank you

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• Multiple foreign keys from one table linking to single primary key in second table

  - by croker10

  Hi all, I have a database with three tables, a household table, an adults table and a users table. The Household table contains two foreign keys, iAdult1ID and iAdult2ID. The Users table has a iUserID primary key and the Adult table has a corresponding iUserID foreign key. One of the columns in the Users table is strUsername, an e-mail address. I am trying to write a query that will allow me to search for an e-mail address for either adult that has a relation to the household. So I have two questions, assuming that all the values are not null, how can I do this? And two, in reality, iAdult2ID can be null, is it still possible to write a query to do this? Thanks for your help. Let me know if you need any more information.

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• please don't ask me to redesign my table and help me with sql query

  - by saurav

  i have a table as given with name and 10 cities in which he lived during his lifetime. name , c1 , c2 ... ,c10. For a particular name i want to fetch other people who have lived in three or more cities lived by this person.

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• Firebird: assign id to existing rows from newly added generator

  - by Aldo

  hello everyone, i have a table whixh contains some rows and dows not have a primary key. I want to add one now, but, is it possible for the existing rows to get an id from the newly added primary key? Dbms: firebird

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• Updating an object with L2S with ASP.NET MVC

  - by Paul

  Is there an easier way to update an object with L2S other then doing it property by property? This is what I am doing now: Public ActionResult Edit(Object obj) { var objToUpdate = _repository.Single<Object>(o => o.id = obj.id); objToUpdate.Prop1 = obj.Prob1; objToUpdate.Prop2 = obj.Prop2; ... _repository.SubmitChanges(); } I am hoping there is a way to just say objToUpdate = obj then submit the changes??? Any help on this would be appreciated!

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• Choosing between a union and a boolean condition

  - by bread

  Does this require a UNION? SELECT vend_id, prod_id, prod_price FROM products WHERE prod_price <= 5 UNION SELECT vend_id, prod_id, prod_price FROM products WHERE vend_id IN (1001,1002); Or is it the same if you do it this way? SELECT vend_id, prod_id, prod_price FROM products WHERE prod_price <= 5 OR vend_id IN (1001,1002);

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• Does introducing foreign keys to MySQL reduce performance

  - by Tam

  I'm building Ruby on Rails 2.3.5 app. By default, Ruby on Rails doesn't provide foreign key contraints so I have to do it manually. I was wondering if introducing foreign keys reduces query performance on the database side enough to make it not worth doing. Performance in this case is my first priority as I can check for data consistency with code. What is your recommendation in general? do you recommend using foreign keys? and how do you suggest I should measure this?

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• mysql replace matching but not changing

  - by alex

  I've used mysql's update replace function before, but even though I think I'm following the same syntax, I can't get this to work-it matches the rows, but doesn't replace. Here's what I'm trying to do: mysql> update contained_widgets set preference_values = replace(preference_values, '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li>', '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li> <li> <a_href="/projects"><span class="not-tc">Projects</span></a></li>'); Query OK, 0 rows affected (0.00 sec) Rows matched: 77 Changed: 0 Warnings: 0 I don't see what I'm missing. Any help is appreciated. I edited "a " to "a_" because the site thinks I'm posting spam links otherwise.

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• Creating a Doctrine query with a different number of ids

  - by frapet

  Is it possible to create a Doctrine query with a differnt number of ids coming from a submitted form? And if yes how? What I am trying to do is this: .... if ($input->isValid()) { $q = Doctrine_Query::create() ->from('Imm_Model_Images i') ->whereIn('i.ImageID = ?', array($input->ids)); $result = $q->fetchArray(); PS: ids come form the submitted form in an array as ids[]. Added Edit: chaged the above line: ->whereIn('i.ImageID = ?', array($input->ids)); with: ->whereIn('i.ImageID = array($input->ids)'); ...and it seems to work.

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• why datetime.now not work when I didn't use tolist?

  - by MemoryLeak

  When I use datacontext.News .Where(p => p.status == true) .Where(p => p.date <= DateTime.Now) .ToList(); the system will return no results; When I use datacontext.News .Where(p => p.status == true) .ToList() .Where(p => p.date <= DateTime.Now) .ToList(); system will return expected results. Can anyone tell me what's up? Thanks in advance !

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• Deleting rows from different tables

  - by Ross

  Here is what i'm trying to do: Delete the project from projects table and all the images associated with that project in the images table Lets say $del_id = 10 DELETE FROM projects, images WHERE projects.p_id = '$del_id' AND images.p_id = '$del_id' What is wrong with this query

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• CakePHP repeats same queries

  - by Rytis

  I have a model structure: Category hasMany Product hasMany Stockitem belongsTo Warehouse, Manufacturer. I fetch data with this code, using containable to be able to filter deeper in the associated models: $this->Category->find('all', array( 'conditions' => array('Category.id' => $category_id), 'contain' => array( 'Product' => array( 'Stockitem' => array( 'conditions' => array('Stockitem.warehouse_id' => $warehouse_id), 'Warehouse', 'Manufacturer', ) ) ), ) ); Data structure is returned just fine, however, I get multiple repeating queries like, sometimes hundreds of such queries in a row, based on dataset. SELECT `Warehouse`.`id`, `Warehouse`.`title` FROM `beta_warehouses` AS `Warehouse` WHERE `Warehouse`.`id` = 2 Basically, when building data structure Cake is fetching data from mysql over and over again, for each row. We have datasets of several thousand rows, and I have a feeling that it's going to impact performance. Is it possible to make it cache results and not repeat same queries?

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• A case-insensitive related implementation problem

  - by Robert

  Hi All, I am going through a final refinement posted by the client, which needs me to do a case-insesitive query. I will basically walk through how this simple program works. First of all, in my Java class, I did a fairly simple webpage parsing: title=(String)results.get("title"); doc = docBuilder.parse("http://" + server + ":" + port + "/exist/rest/db/wb/xql/media_lookup.xql?" + "&title=" + title); This Java statement references an XQuery file "media_lookup.xql" which is stored on localhost, and the only parameter we are passing is the string "title". Secondly, let's take at look at that XQuery file: $title := request:get-parameter('title',""), $mediaNodes := doc('/db/wb/portfolio/media_data.xml'), $query := $mediaNodes//media[contains(title,$title)], Then it will evaluate that query. This XQuery will get the "title" parameter that are passes from our Java class, and query the "media_data" xml file stored in the database, which contains a bunch of media nodes with a 'title' element node. As you may expect, this simple query will just match those media nodes whose 'title' element contains a substring of what the value of string 'title' is. So if our 'title' is "Chi", it will return media nodes whose title may be "Chicago" or "Chicken". The refinment request posted by the client is that there should be NO case-sensitivity. The very intuitive way is to modify the XQuery statement by using a lower-case funtion in it, like: $query := $mediaNodes//media[contains(lower-case(title/text(),lower-case($title))], However, the question comes: this modified query will run my machine into memory overflow. Since my "media_data.xml" is quite huge and contains thouands of millions of media nodes, I assume the lower-case() function will run on each of the entries, thus causing the machine to crash. I've talked with some experienced XQuery programmer, and they think I should use an index to solve this problem, and I will definitely research into that. But before that, I am just posting this problem here to get other ideas or any suggestions, do you think any other way may help? for example, could I tweak the Java parse statement to realize the case-insensitivity? Since I think I saw some people did some string concatination by using "contains." in Java before passing it to the server. Any idea or help is welcomed, thanks in advance.

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