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  • Ruby on Rails ActiveRecord/Include/Associations can't get my query to work

    - by Cypher
    I just started learning Rails and I'm just trying to set up query via associations. All the queries I try to write seem to be doing bizzare things and end up trying to query two tables parsed together with an '_' as one table. I have no clue why this would ever happen My tables are as follows: schools: id name variables: id name type var_entries: id variable_id entry school_entries: id school_id var_entry_id my rails association tables are $local = { :adapter => "mysql", :host => "localhost", :port => "3306".to_i, :database => "spy_2", :username =>"root", :password => "vertrigo" } class School < ActiveRecord::Base establish_connection $local has_many :school_entries has_many :var_entries, :through => school_entries end class Variable < ActiveRecord::Base establish_connection $local has_many :var_entries has_many :school_entries, :through => :var_entries end class VarEntry < ActiveRecord::Base establish_connection $local has_many_and_belongs_to :school_entries belongs_to :variables end class SchoolEntry < ActiveRecord::Base establish_connection $local belongs_to :school has_many :var_entries end I want to do this sql query: SELECT school_id, variable_id,rank FROM school_entries, variables, var_entries, schools WHERE var_entries.variable_id = variables.id AND school_entries.var_entry_id = var_entries.id AND schools.id = school_entries.school_id AND variables.type = 'number'; and put it into Rails notation: here is one of my many failed attempts schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "variables.type = 'number'") the error: 'const_missing': uninitialized constant VarEntry::Variables (NameError) if i remove variables schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "type = 'number'") the error is: Mysql::Error: Unkown column 'type' in 'where clause': SELECT * FROM 'var_entries' WHERE (type=number) (ActiveRecord::StatementInvalid) Can anyone tell me where I'm going horribly wrong?

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  • Query gives an unsorted result set when run from stored procedure using CTE

    - by irtizaur
    I am trying to create a paging query using CTE. It works fine when I execute it from Microsoft SQL Server Management Studio Query Editor. And the result set is perfectly sorted as I want. But when I modify it for a stored procedure it gives me a unsorted result and I don't have any clue why. Here is my Query, with items as ( select ROW_NUMBER() over (order by create_time desc) number , i.item_name item_name , i.create_time create_time , c.category_name category_name , i.category_id category_id from cb_item i, cb_category c where i.category_id = c.category_id and c.category_id = '4E5248FE-05DD-4D01-ABBB-80C6E3BA5CDA' ) select item_name , create_time , category_name , category_id from items where number between 1 and 25 And this is the Stored Procedure Version, create procedure ItemPage @category_id uniqueidentifier , @from int , @to int , @sortby nvarchar(50) as begin with items as ( select ROW_NUMBER() over (order by @sortby) number , i.item_name item_name , i.create_time create_time , c.category_name category_name , i.category_id category_id from cb_item i, cb_category c where i.category_id = c.category_id and c.category_id = @category_id ) select item_name , create_time , category_name , category_id from items where number between @from and @to end exec itempage '4E5248FE-05DD-4D01-ABBB-80C6E3BA5CDA' , 1, 25, 'create_time desc' The first one gives me sorted result but procedure gives me unsorted result. I don't know why?

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  • When optimizing database queries, what exactly is the relationship between number of queries and siz

    - by williamjones
    To optimize application speed, everyone always advises to minimize the number of queries an application makes to the database, consolidating them into fewer queries that retrieve more wherever possible. However, this also always comes with the caution that data transferred is still data transferred, and just because you are making fewer queries doesn't make the data transferred free. I'm in a situation where I can over-include on the query in order to cut down the number of queries, and simply remove the unwanted data in the application code. Is there any type of a rule of thumb on how much of a cost there is to each query, to know when to optimize number of queries versus size of queries? I've tried to Google for objective performance analysis data, but surprisingly haven't been able to find anything like that. Clearly this relationship will change for factors such as when the database grows in size, making this somewhat individualized, but surely this is not so individualized that a broad sense of the landscape can't be drawn out? I'm looking for general answers, but for what it's worth, I'm running an application on Heroku.com, which means Ruby on Rails with a Postgres database.

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  • WMI Query Script as a Job

    - by Kenneth
    I have two scripts. One calls the other with a list of servers as parameters. The second query is designed to execute a WMI query. When I run it manually, it does this perfectly. When I try to run it as a job it hangs forever and I have to remove it. For the sake of space here is the relevant part of the calling script: ProcessServers.ps1 Start-Job -FilePath .\GetServerDetailsLight.ps1 -ArgumentList $sqlsrv,$destdb,$server,$instance GetServerDetailsLight.ps1 param($sqlsrv,$destdb,$server,$instance) $password = get-content C:\SQLPS\auth.txt | convertto-securestring $credentials = new-object -typename System.Management.Automation.PSCredential -argumentlist "DOMAIN\MYUSER",$password [System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SqlServer.SMO') $box_id = 0; if ($sqlsrv.length -eq 0) { write-output "No data passed" break } function getinfo { param( [string]$svr, [string]$inst ) "Entered GetInfo with: $svr,$inst" $cs = get-wmiobject win32_operatingsystem -computername $svr -credential $credentials -authentication 6 -Verbose -Debug | select Name, Model, Manufacturer, Description, DNSHostName, Domain, DomainRole, PartOfDomain, NumberOfProcessors, SystemType, TotalPhysicalMemory, UserName, Workgroup write-output "WMI Results: $cs" } getinfo $server $instance write-output "Complete" Executed as a job it will show as 'running' forever: PS C:\sqlps> Start-Job -FilePath .\GetServerDetailsLight.ps1 -ArgumentList DBSERVER,LOGDB,SERVER01,SERVER01 Id Name State HasMoreData Location Command -- ---- ----- ----------- -------- ------- 21 Job21 Running True localhost param($sqlsrv,$destdb,... GAC Version Location --- ------- -------- True v2.0.50727 C:\WINDOWS\assembly\GAC_MSIL\Microsoft.SqlServer.Smo\10.0.0.0__89845dcd8080cc91\Microsoft.SqlServer.Smo.dll getinfo MSDCHR01 MSDCHR01 Entered GetInfo with: SERVER01,SERVER01 The last output I ever get is the 'Entered GetInfo with: SERVER01,SERVER01'. If I run it manually like so: PS C:\sqlps> .\GetServerDetailsLight.ps1 DBSERVER LOGDB SERVER01 SERVER01 The WMI query executes just as expected. I am trying to determine why this is, or at least a useful way to trap errors from within jobs. Thanks!

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  • Problem Writing Linq2Xml Query

    - by Gavin Draper
    I'm trying to write a Linq2XML query to query the following XML. I need it to pull back all photos for a given GalleryID. <Albums> <Album GalleryId="1" Cover="AlbumCover1.jpg" Title="Album 1"> <Photos> <Photo Title="Image1" URL="img1.jpg" DateAdded="01/01/2010 09:20"/> <Photo Title="Image2" URL="img2.jpg" DateAdded="01/01/2010 09:20"/> <Photo Title="Image3" URL="img3.jpg" DateAdded="01/01/2010 09:20"/> </Photos> </Album> <Album GalleryId="2" Cover="AlbumCover1.jpg" Title="Album 2"> <Photos> <Photo Title="Image1" URL="img1.jpg" DateAdded="01/01/2010 09:20"/> <Photo Title="Image2" URL="img2.jpg" DateAdded="01/01/2010 09:20"/> </Photos> </Album> </Albums> The best I've come up with is XDocument xmlDoc = XDocument.Load(GalleryFilePath); var x = from c in xmlDoc.Descendants("Album") where c.Attribute("GalleryId").Equals(GalleryId) orderby c.Attribute("Title").Value descending select new { Title = c.Element("Photo").Attribute("Title"), URL = c.Element("Photo").Attribute("URL"), DateAdded = c.Element("Photo").Attribute("DateAdded") }; This returns nothing, I'm guessing this is because I'm telling it to query the Album element then trying to loop through the photo elements. Any tips as to how this should be done? Thanks

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  • MySQL ORDER BY DESC is fast but ASC is very slow

    - by Pepper
    Hello, I'm completely stumped on this one. For some reason when I sort this query by DESC it's super fast, but if sorted by ASC it's extremely slow. This takes about 150 milliseconds: SELECT posts.id FROM posts USE INDEX (published) WHERE posts.feed_id IN ( 4953,622,1,1852,4952,76,623,624,10 ) ORDER BY posts.published DESC LIMIT 0, 50; This takes about 32 seconds: SELECT posts.id FROM posts USE INDEX (published) WHERE posts.feed_id IN ( 4953,622,1,1852,4952,76,623,624,10 ) ORDER BY posts.published ASC LIMIT 0, 50; The EXPLAIN is the same for both queries. id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE posts index NULL published 5 NULL 50 Using where I've tracked it down to "USE INDEX (published)". If I take that out it's the same performance both ways. But the EXPLAIN shows the query is less efficient overall. id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE posts range feed_id feed_id 4 \N 759 Using where; Using filesort And here's the table. CREATE TABLE `posts` ( `id` int(20) NOT NULL AUTO_INCREMENT, `feed_id` int(11) NOT NULL, `post_url` varchar(255) NOT NULL, `title` varchar(255) NOT NULL, `content` blob, `author` varchar(255) DEFAULT NULL, `published` int(12) DEFAULT NULL, `updated` datetime NOT NULL, `created` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `post_url` (`post_url`,`feed_id`), KEY `feed_id` (`feed_id`), KEY `published` (`published`) ) ENGINE=InnoDB AUTO_INCREMENT=196530 DEFAULT CHARSET=latin1; Is there a fix for this? Thanks!

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  • do console apps run faster than windows based app?

    - by omair iqbal
    i am reletivly new to world of programming i have a few performance questions 1. do console apps run faster than windows based app? 2.are languages like c and pascal faster than object oriented languages like c++ and delphi?i know language speed depends more on compiler than on language itself but do compilers for prcedural languages like c and pascal produce faster code than oo ones like delphi,c++(including c++ compilers that can procuce c code) sorry for my bad english

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  • Algorithm To Select Most Popular Places from Database

    - by Russell C.
    We have a website that contains a database of places. For each place our users are able to take one of the follow actions which we record: VIEW - View it's profile RATING - Rate it on a scale of 1-5 stars REVIEW - Review it COMPLETED - Mark that they've been there WISH LIST - Mark that they want to go there FAVORITE - Mark that it's one of their favorites In our database table of places each place contains a count of the number of times each action above was taken as well as the average rating given by users. views ratings avg_rating completed wishlist favorite What we want to be able to do is generate lists of the top places using the above information. Ideally, we would want to be able to generate this list using a relatively simple SQL query without needing to do any legwork to calculate additional fields or stack rank places against one another. That being said, since we only have about 50,000 places we could run a nightly cron job to calculate some fields such as rankings on different categories if it would make a meaningful difference in the overall results of our top places. I'd appreciate if you could make some suggestions on how we should think about bubbling the best places to the top, which criteria we should weight more heavily, and given that information - suggest what the MySQL query would need to look like in order to select the top 10 places. One thing to note is that at this time we are less concerned with the recency of a place being popular - meaning that looking at the aggregate information is fine and that more recent data doesn't need to be weighted more heavily. Thanks in advance for your help & advice!

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  • Are there any drawbacks to using helper :all in Rails

    - by Rob Jones
    In Rails 'helper :all' makes all your helpers 'available' to all your controllers. This is concise and convenient, but does it have any memory and/or performance implications compared to explicitly calling the helpers that each controller actually needs? It's unclear form the docs whether using it involves 'require'ing all those files, or whether autoload is being used. I can't tell from the source in the Rails framework docs. thanks

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  • Do console apps run faster than GUI apps?

    - by omair iqbal
    I am relatively new to world of programming. I have a few performance questions: Do console apps run faster than apps with a graphical user interface? Are languages like C and Pascal faster than object oriented languages like C++ and Delphi? I know language speed depends more on compiler than on language itself, but do compilers for procedural languages produce faster code than OO ones (including C++ compilers that can produce C code)?

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  • Using Perfmon with MySQL Connector/NET

    - by Mark Richman
    I am trying to diagnose repeated lock wait timeouts from my ASP.NET app to MySQL 5.1. I'm using MySQL Connector/NET 6.2.3. I don't see anything MySQL-related in Perfmon's Performance Object dropdown list. What else can I do to try to diagnose these issues?

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  • How to get the FPS from a JavaFX scene?

    - by valmar
    I am currently writing a small graphical performance test benchmark for JavaFX. Thus, I need to get the current FPS at which the JavaFX scene is being refreshed. So far, I haven't found a solution how to accomplish this. Does anyone know if there is some kind of event that I could use in order to get the FPS?

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  • random data using php & mysql

    - by Prakash
    I have mysql database structure like below: CREATE TABLE test ( id int(11) NOT NULL auto_increment, title text NULL, tags text NULL, PRIMARY KEY (id) ); data on field tags is stored as a comma separated text like html,php,mysql,website,html etc... now I need create an array that contains around 50 randomly selected tags from random records. currently I am using rand() to select 15 random mysql data from database and then holding all the tags from 15 records in an array. Then I am using array_rand() for randomizing the array and selecting only 50 random records. $query=mysql_query("select * from test order by id asc, RAND() limit 15"); $tags=""; while ($eachData=mysql_fetch_array($query)) { $additionalTags=$eachData['tags']; if ($tags=="") { $tags.=$additionalTags; } else { $tags.=$tags.",".$additionalTags; } } $tags=explode(",", $tags); $newTags=array(); foreach ($tags as $tag) { $tag=trim($tag); if ($tag!="") { if (!in_array($tag, $newTags)) { $newTags[]=$tag; } } } $random_newTags=array_rand($newTags, 50); Now I have huge records on the database, and because of that; rand() is performing very slow and sometimes it doesn't work. So can anyone let me know how to handle this situation correctly so that my page will work normally.

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  • SQL query in JSP file pulling variable from VXML file

    - by s1066
    Hi I'm trying to get an SQL query to work within a JSP file. The JSP file is pulled by a VXML file here is my JSP file code: <?xml version="1.0"?> <%@ page import="java.util.*" %> <%@ page import="java.sql.*" %> <% boolean success = true; // Always optimistic String info = ""; String schoolname = request.getParameter("schoolname"); String informationtype = request.getParameter("informationtype"); try { Class.forName("org.postgresql.Driver"); String connectString = "jdbc:postgresql://localhost:5435/N0176359"; String user = "****"; String password = "*****"; Connection conn = DriverManager.getConnection(connectString, user, password); Statement st = conn.createStatement(); ResultSet rsvp = st.executeQuery("SELECT * FROM lincolnshire_school_information_new WHERE school_name=\'"+schoolname+"\'"); rsvp.next(); info = rsvp.getString(2); }catch (ClassNotFoundException e) { success = false; // something went wrong } %> As you can see I'm trying to insert the value of the variable declared as "schooname" into the end of the SQL query. However when I come to run the jsp file it doesn't work and I get an error "ResultSet not positioned properly". When I put a standard query in (without trying to make it value of the variable it works fine) Hope that makes sense, and thank you for any help!

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  • How to access Youtube_it ruby query results?

    - by spectro
    I am trying to implement the youtube_it youtube api wrapper for ruby and have it working except I'm stumped as to how the query results should be accessed. Here is my query: client.videos_by(:query => "penguin", :max_results => 1) Submitting request [url=http://gdata.youtube.com/feeds/api/videos?max-results=1&start-index=1&vq=penguin]. => #<YouTubeIt::Response::VideoSearch:0xb6c41b14 @feed_id="http://gdata.youtube.com/feeds/api/videos", @updated_at=Wed Nov 03 18:01:39 UTC 2010, @videos=[#<YouTubeIt::Model::Video:0xb6c424d8 @thumbnails=[#<YouTubeIt::Model::Thumbnail:0xb6c6b694 @url="http://i.ytimg.com/vi/oSbLpQEZP1Y/2.jpg", @width=120, @height=90, @time="00:01:34">, #<YouTubeIt::Model::Thumbnail:0xb6c6b248 @url="http://i.ytimg.com/vi/oSbLpQEZP1Y/1.jpg", @width=120, @height=90, @time="00:00:47">, #<YouTubeIt::Model::Thumbnail:0xb6c6a988 @url="http://i.ytimg.com/vi/oSbLpQEZP1Y/3.jpg", @width=120, @height=90, @time="00:02:21">, #<YouTubeIt::Model::Thumbnail:0xb6c69e34 @url="http://i.ytimg.com/vi/oSbLpQEZP1Y/0.jpg", @width=320, @height=240, @time="00:01:34">], @categories=[#<YouTubeIt::Model::Category:0xb6ca5d6c @term="Music", @label="Music">], @noembed=false, @racy=false, @favorite_count=7862, @duration=188, @author=#<YouTubeIt::Model::Author:0xb6c9942c @name="wili", @uri="http://gdata.youtube.com/feeds/api/users/wili">, @updated_at=Tue Nov 02 08:45:25 UTC 2010, @longitude=nil, @position=nil, @view_count=1682350, @html_content="penguin", @media_content=[#<YouTubeIt::Model::Content:0xb6c770d4 @url="http://www.youtube.com/v/oSbLpQEZP1Y?f=videos&app=youtube_gdata", @duration=188, @format=#<YouTubeIt::Model::Video::Format:0xb656d108 @name=:swf, @format_code=5>, @default=true, @mime_type="application/x-shockwave-flash">, #<YouTubeIt::Model::Content:0xb6c766d4 @url="rtsp://v5.cache3.c.youtube.com/CiILENy73wIaGQlWPxkBpcsmoRMYDSANFEgGUgZ2aWRlb3MM/0/0/0/video.3gp", @duration=188, @format=#<YouTubeIt::Model::Video::Format:0xb656d11c @name=:rtsp, @format_code=1>, @default=false, @mime_type="video/3gpp">, #<YouTubeIt::Model::Content:0xb6c75d38 @url="rtsp://v8.cache3.c.youtube.com/CiILENy73wIaGQlWPxkBpcsmoRMYESARFEgGUgZ2aWRlb3MM/0/0/0/video.3gp", @duration=188, @format=#<YouTubeIt::Model::Video::Format:0xb656d0f4 @name=:three_gpp, @format_code=6>, @default=false, @mime_type="video/3gpp">], @description="penguin", @latitude=nil, @title="penguin", @published_at=Mon May 08 18:11:01 UTC 2006, @player_url="http://www.youtube.com/watch?v=oSbLpQEZP1Y&feature=youtube_gdata_player", @rating=#<YouTubeIt::Model::Rating:0xb6c5eb4c @min=1, @max=5, @average=4.676985, @rater_count=2746>, @keywords=["pigloo", "penguin"], @video_id="http://gdata.youtube.com/feeds/api/videos/oSbLpQEZP1Y", @where=nil>], @total_result_count=291282, @offset=1, @max_result_count=1> I would like to retrieve the URL and thumbnail links. Any ideas?

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  • SQL: Need help with query construction.

    - by Geeknidas
    Hi Guys, I am relatively new with sql and I need some help with some basic query construction. Problem: To retrieve the number of orders and the customer id from a table based on a set of parameters. I want to write a query to figure out the number of orders under each customer (Column: Customerid) along with the CustomerID where the number of orders should be greater or equal to 10 and the status of the order should be Active. Moreover, I also want to know the first transaction date of an order belonging to each customerid. Table Description: product_orders Orderid CustomerId Transaction_date Status ------- ---------- ---------------- ------- 1 23 2-2-10 Active 2 22 2-3-10 Active 3 23 2-3-10 Deleted 4 23 2-3-10 Active Query that I have written: select count(*), customerid from product_orders where status = 'Active' GROUP BY customerid ORDER BY customerid; The above statement gives me the sum of all order under a customer id but does not fulfil the condition of atleast 10 orders. I donot know how to display the first transaction date along with the order under a customerid (status: could be active or delelted doesn't matter) Ideal solutions should look like: Total Orders CustomerID Transaction Date (the first transaction date) ------------ ---------- ---------------- 11 23 1-2-10 Thanks in advance. I hope you guys would be kind enough to stop by and help me out. Cheers, Leonidas

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  • Saving and retrieving image in SQL database from C# problem

    - by Mobin
    I used this code for inserting records in a person table in my DB System.IO.MemoryStream ms = new System.IO.MemoryStream(); Image img = Image_Box.Image; img.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp); this.personTableAdapter1.Insert(NIC_Box.Text.Trim(), Application_Box.Text.Trim(), Name_Box.Text.Trim(), Father_Name_Box.Text.Trim(), DOB_TimePicker.Value.Date, Address_Box.Text.Trim(), City_Box.Text.Trim(), Country_Box.Text.Trim(), ms.GetBuffer()); but when i retrieve this with this code byte[] image = (byte[])Person_On_Application.Rows[0][8]; MemoryStream Stream = new MemoryStream(); Stream.Write(image, 0, image.Length); Bitmap Display_Picture = new Bitmap(Stream); Image_Box.Image = Display_Picture; it works perfectly fine but if i update this with my own generated Query like System.IO.MemoryStream ms = new System.IO.MemoryStream(); Image img = Image_Box.Image; img.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp); Query = "UPDATE Person SET Person_Image ='"+ms.GetBuffer()+"' WHERE (Person_NIC = '"+NIC_Box.Text.Trim()+"')"; the next time i use the same code for retrieving the image and displaying it as used above . Program throws an exception

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  • Is there a way to generate a short random id, avoiding collisions, without hitting persistent storag

    - by bshacklett
    If you've used GoToMeeting, that's the type of ID I want. I'd like it to be random so that it obfuscates the number of items being tracked and short, so that it's easy to reference manually; UUIDs are way too long. I'd like to avoid hitting persistent storage merely for performance reasons, but I can't think of any other way to avoid collisions. Is 9 digits enough to do something time-based?

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  • jdbc query - date ranges as parameters

    - by pstanton
    Hi all, I'd like to write a single JDBC statement that can handle the equivalent of any number of NOT BETWEEN date1 AND date2 where clauses. By single query, i mean that the same SQL string will be used to create the JDBC statements and then have different parameters supplied. This is so that the underlying frameworks can efficiently cache the query (i've been stung by that before). Essentially, I'd like to find a query that is the equivalent of SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? and at the same time could be used with fewer parameters: SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? or more parameters SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? I will consider using a temporary table if that will be simpler and more efficient. thanks for the help!

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  • How to handle large dataset with JPA (or at least with Hibernate)?

    - by Roman
    I need to make my web-app work with really huge datasets. At the moment I get either OutOfMemoryException or output which is being generated 1-2 minutes. Let's put it simple and suppose that we have 2 tables in DB: Worker and WorkLog with about 1000 rows in the first one and 10 000 000 rows in the second one. Latter table has several fields including 'workerId' and 'hoursWorked' fields among others. What we need is: count total hours worked by each user; list of work periods for each user. The most straightforward approach (IMO) for each task in plain SQL is: 1) select Worker.name, sum(hoursWorked) from Worker, WorkLog where Worker.id = WorkLog.workerId group by Worker.name; //results of this query should be transformed to Multimap<Worker, Long> 2) select Worker.name, WorkLog.start, WorkLog.hoursWorked from Worker, WorkLog where Worker.id = WorkLog.workerId; //results of this query should be transformed to Multimap<Worker, Period> //if it was JDBC then it would be vitally //to set resultSet.setFetchSize (someSmallNumber), ~100 So, I have two questions: how to implement each of my approaches with JPA (or at least with Hibernate); how would you handle this problem (with JPA or Hibernate of course)?

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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