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• Acquiring Table Lock in Database - Interview Question

  - by harigm

  One of my interview Questions, if multiple users across the world are accessing the application, in which it uses a Table which has a Primary Key as Auto Increment Field. The Question how can you prevent the other user getting the Same Primary key when the other user is executing? My answer was I will obtain the Lock on the table and I will make the user to wait Until that user is released with the Primary key. But the Question How do you acquire the Table lock programmatically and implement this? If there are 1000 users coming every minute to the application, if you explicity hold the lock on the table, then the application will become slower? How do you manage this? Please suggest the possible answers for the above question

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• Is my understanding of "select distinct" correct?

  - by paxdiablo

  We recently discovered a performance problem with one of our systems and I think I have the fix but I'm not certain my understanding is correct. In simplest form, we have a table blah into which we accumulate various values based on a key field. The basic form is: recdate date rectime time system varchar(20) count integer accum1 integer accum2 integer There are a lot more accumulators than that but they're all of the same form. The primary key is made up of recdate, rectime and system. As values are collected to the table, the count for a given recdate/rectime/system is incremented and the values for that key are added to the accumulators. That means the averages can be obtained by using accumN / count. Now we also have a view over that table specified as follows: create view blah_v ( recdate, rectime, system, count, accum1, accum2 ) as select distinct recdate, rectime, system, count, value (case when count > 0 then accum1 / count end, 0), value (case when count > 0 then accum2 / count end, 0) from blah; In other words, the view gives us the average value of the accumulators rather than the sums. It also makes sure we don't get a divide-by-zero in those cases where the count is zero (these records do exist and we are not allowed to remove them so don't bother telling me they're rubbish - you're preaching to the choir). We've noticed that the time difference between doing: select distinct recdate from XX varies greatly depending on whether we use the table or the view. I'm talking about the difference being 1 second for the table and 27 seconds for the view (with 100K rows). We actually tracked it back to the select distinct. What seems to be happening is that the DBMS is actually loading all the rows in and sorting them so as to remove duplicates. That's fair enough, it's what we stupidly told it to do. But I'm pretty sure the fact that the view includes every component of the primary key means that it's impossible to have duplicates anyway. We've validated the problem since, if we create another view without the distinct, it performs at the same speed as the underlying table. I just wanted to confirm my understanding that a select distinct can not have duplicates if it includes all the primary key components. If that's so, then we can simply change the view appropriately.

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• asp.net mvc insert doesnt seem to work for me....

  - by Pandiya Chendur

  My controller's call to repository insert method all the values are passed but it doesn't get inserted in my table.. My controller method, [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create([Bind(Exclude = "Id")]FormCollection collection) { try { MaterialsObj materialsObj = new MaterialsObj(); materialsObj.Mat_Name = collection["Mat_Name"]; materialsObj.Mes_Id = Convert.ToInt64(collection["MeasurementType"]); materialsObj.Mes_Name = collection["Mat_Type"]; materialsObj.CreatedDate = System.DateTime.Now; materialsObj.CreatedBy = Convert.ToInt64(1); materialsObj.IsDeleted = Convert.ToInt64(1); consRepository.createMaterials(materialsObj); return RedirectToAction("Index"); } catch { return View(); } } and my repository, public MaterialsObj createMaterials(MaterialsObj materialsObj) { Material mat = new Material(); mat.Mat_Name = materialsObj.Mat_Name; mat.Mat_Type = materialsObj.Mes_Name; mat.MeasurementTypeId = materialsObj.Mes_Id; mat.Created_Date = materialsObj.CreatedDate; mat.Created_By = materialsObj.CreatedBy; mat.Is_Deleted = materialsObj.IsDeleted; db.Materials.InsertOnSubmit(mat); return materialsObj; } What am i missing here any suggestion....

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• Testing the context in asp.net mvc

  - by user252160

  I got pretty experienced with testing controllers, my question here is though, aren't we supposed to test the data context as well, and how ? I mean, there are a lot of relationships and constraints coming from the DB that simply testing controllers does not cover. On the other hand, testing against the DB is not considered a good practice - what then ? Simply testing without db.SubmitChanges() or what ?

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• Bus Timetable database design

  - by paddydub

  hi, I'm trying to design a db to store the timetable for 300 different bus routes, Each route has a different number of stops and different times for Monday-Friday, Saturday and Sunday. I've represented the bus departure times for each route as follows, I'm not sure if i should have null values in the table, does this look ok? route,Num,Day, t1, t2, t3, t4 t5 t6 t7 t8 t9 t10 117, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 null null null 117, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 null null null 117, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 null null null 117, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 null null null . . . 117, 20, Monday, 9:39, 10.09, 11:39, 12:39, 14:39 18:39 19:39 null null null 119, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 20:00 21:00 22:00 119, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 20:03 21:03 22:03 119, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 20:06 21:06 22:06 119, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 20:09 21:09 22:09 . . . 119, 37, Monday, 9:49, 9:59, 11:59, 12:59, 14:59 18:59 19:59 20:59 21:59 22:59 139, 1, Sunday, 9:00, 9:30, 20:00 21:00 22:00 null null null null null 139, 2, Sunday, 9:03, 9:33, 20:03 21:03 22:03 null null null null null 139, 3, Sunday, 9:06, 9:36, 20:06 21:06 22:06 null null null null null 139, 4, Sunday, 9:09, 9:39, 20:09 21:09 22:09 null null null null null . . . 139, 20, Sunday, 9:49, 9:59, 20:59 21:59 22:59 null null null null null

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• Representing Sparse Data in PostgreSQL

  - by Chris S

  What's the best way to represent a sparse data matrix in PostgreSQL? The two obvious methods I see are: Store data in a single a table with a separate column for every conceivable feature (potentially millions), but with a default value of NULL for unused features. This is conceptually very simple, but I know that with most RDMS implementations, that this is typically very inefficient, since the NULL values ususually takes up some space. However, I read an article (can't find its link unfortunately) that claimed PG doesn't take up data for NULL values, making it better suited for storing sparse data. Create separate "row" and "column" tables, as well as an intermediate table to link them and store the value for the column at that row. I believe this is the more traditional RDMS solution, but there's more complexity and overhead associated with it. I also found PostgreDynamic, which claims to better support sparse data, but I don't want to switch my entire database server to a PG fork just for this feature. Are there any other solutions? Which one should I use?

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• MySQL optimized sentence

  - by Ivan

  I have a simple table where I have to extract some records. The problem is that the evaluation function is a very time-consuming stored procedure so I shouldn't to call it twice like in this sentence: SELECT *, slow_sp(row) FROM table WHERE slow_sp(row)>0 ORDER BY dist DESC LIMIT 10 First I thought in optimize like this: SELECT *, slow_sp(row) AS value FROM table WHERE value>0 ORDER BY dist DESC LIMIT 10 But it doesn't works due "value" is not processed when the WHERE clause is evaluated. Any idea to optimize this sentence? Thanks.

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• Problem with interface implementation in partial classes.

  - by Bas

  I have a question regarding a problem with L2S, Autogenerated DataContext and the use of Partial Classes. I have abstracted my datacontext and for every table I use, I'm implementing a class with an interface. In the code below you can see I have the Interface and two partial classes. The first class is just there to make sure the class in the auto-generated datacontext inherets Interface. The other autogenerated class makes sure the method from Interface is implemented. namespace PartialProject.objects { public interface Interface { Interface Instance { get; } } //To make sure the autogenerated code inherits Interface public partial class Class : Interface { } //This is autogenerated public partial class Class { public Class Instance { get { return this.Instance; } } } } Now my problem is that the method implemented in the autogenerated class gives the following error: - Property 'Instance' cannot implement property from interface 'PartialProject.objects.Interface'. Type should be 'PartialProjects.objects.Interface'. <- Any idea how this error can be resolved? Keep in mind that I can't edit anything in the autogenerated code. Thanks in advance!

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• Trouble with LINQ databind to GridView and RowDataBound

  - by Michael

  Greetings all, I am working on redesigning my personal Web site using VS 2008 and have chosen to use LINQ to create by data-access layer. Part of my site will be a little app to help manage my budget better. My first LINQ query does successfully execute and display in a GridView, but when I try to use a RowDataBound event to work with the results and refine them a bit, I get the error: The type or namespace name 'var' could not be found (are you missing a using directive or an assembly reference?) This interesting part is, if I just try to put in a var s = "s"; anywhere else in the same file, I get the same error too. If I go to other files in the web project, var s = "s"; compiles fine. Here is the LINQ Query call: public static IQueryable pubGetRecentTransactions(int param_accountid) { clsDataContext db; db = new clsDataContext(); var query = from d in db.tblMoneyTransactions join p in db.tblMoneyTransactions on d.iParentTransID equals p.iTransID into dp from p in dp.DefaultIfEmpty() where d.iAccountID == param_accountid orderby d.dtTransDate descending, d.iTransID ascending select new { d.iTransID, d.dtTransDate, sTransDesc = p != null ? p.sTransDesc : d.sTransDesc, d.sTransMemo, d.mTransAmt, d.iCheckNum, d.iParentTransID, d.iReconciled, d.bIsTransfer }; return query; } protected void Page_Load(object sender, EventArgs e) { if (!this.IsPostBack) { this.prvLoadData(); } } internal void prvLoadData() { prvCtlGridTransactions.DataSource = clsMoneyTransactions.pubGetRecentTransactions(2); prvCtlGridTransactions.DataBind(); } protected void prvCtlGridTransactions_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { var datarow = e.Row.DataItem; var s = "s"; e.Row.Cells[0].Text = datarow.dtTransDate.ToShortDateString(); e.Row.Cells[1].Text = datarow.sTransDesc; e.Row.Cells[2].Text = datarow.mTransAmt.ToString("c"); e.Row.Cells[3].Text = datarow.iReconciled.ToString(); }//end if }//end RowDataBound My googling to date hasn't found a good answer, so I turn it over to this trusted community. I appreciate your time in assisting me.

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• Help to choose NoSQL database for project

  - by potapuff

  There is a table: doc_id(integer)-value(integer) Approximate 100k doc_id and 27?? rows. Majority query on this table - searching documents similar to current document: select 10 documents with maximum of (count common to current document value)/(count ov values in document). Nowadays we use PostgreSQL. Table weight (with index) ~1,5 GB. Average query time ~0.5s. Should I transfer all this to NoSQL base, if so, what?

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• ALTER TABLE on dependant column

  - by Sharmi

  I am trying to alter column datatype of a primary key to tinyint from int.This column is a foreign key in other tables.So,I get the following error: Msg 5074, Level 16, State 1, Line 1 The object 'PK_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Details_tbl_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Log_tbl_User_tbl' is dependent on column 'appId'. Msg 4922, Level 16, State 9, Line 1 ALTER TABLE ALTER COLUMN appId failed because one or more objects access this column. Howw should i rectify this?

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• C# code for viewev tables

  - by simon

  Can somebody write me a code, how to view data from tables in c# (using select statement)? I tried it myself and posted the code here, but i didn't get it right. Please help!

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• Foreign keys and pagination

  - by whitstone86

  This is my pagination script: <?php /*********************************** * PhpMyCoder Paginator * * Created By PhpMyCoder * * 2010 PhpMyCoder * * ------------------------------- * * You may use this code as long * * as this notice stays intact and * * the proper credit is given to * * the author. * ***********************************/ ?> <head> <title> Pagination Test - Created By PhpMyCoder</title> <style type="text/css"> #nav { font: normal 13px/14px Arial, Helvetica, sans-serif; margin: 2px 0; } #nav a { background: #EEE; border: 1px solid #DDD; color: #000080; padding: 1px 7px; text-decoration: none; } #nav strong { background: #000080; border: 1px solid #DDD; color: #FFF; font-weight: normal; padding: 1px 7px; } #nav span { background: #FFF; border: 1px solid #DDD; color: #999; padding: 1px 7px; } </style> </head> <?php //Require the file that contains the required classes include("pmcPagination.php"); //PhpMyCoder Paginator $paginator = new pmcPagination(20, "page"); //Connect to the database mysql_connect("localhost","root","PASSWORD"); //Select DB mysql_select_db("tvguide"); //Select only results for today and future $result = mysql_query("SELECT programme, channel, airdate, expiration, episode, setreminder FROM epdata1 where airdate >= now() order by expiration GROUP BY airdate"); //You can also add reuslts to paginate here mysql_data_seek($queryresult,0) ; while($row = mysql_fetch_array($result)) { $paginator->add(new paginationData($row['programme'], $row['channel'], $row['airdate'], $row['expiration'], $row['episode'], $row['setreminder'])); } ?> <?php //Show the paginated results $paginator->paginate (); ?><? include("pca-footer1.php"); ?> <?php //Show the navigation $paginator->navigation(); ?> However, I have two tables in this, and they are epdata1 (where the airtimes for my show House M.D. are) and housemdep plus the setreminder table. How can I use foreign keys in relation to this? I'm not sure if this will work for my script, but am willing to try. What I would like to do is to select certain episodes from the table housemdep (episodes of the show) and if any are selected it shows them as this: House M.D. showing on Channel 1 June 6th - 8:00pm "Wilson" Set Reminder House M.D. showing on Channel 1 June 7th - 1:30am "Wilson" Set Reminder House M.D. showing on Channel 1 June 7th - 12:55pm "House's Head" Set Reminder or like this, if I have not selected an episode from the row: House M.D. showing on Channel 1 June 7th - 8:00pm "House's Head" Set Reminder House M.D. showing on Channel 1 June 8th - 9:00pm Set Reminder House M.D. showing on Channel 1 June 9th - 2:30pm Set Reminder House M.D. showing on Channel 1 June 7th - 8:00pm "Que Sera Sera" Set Reminder Foreign keys and relationship of interlinked tables are new to me, if anyone could help I'd appreciate this. I've tried some of what Google suggested on foreign keys in another version of this script (this is a clone of the original on my localhost server running Apache and PHP 5.28/MySQL), but am not sure how to implement this. Thanks.

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• I need some help optimizing my database schema

  - by Steffan

  Here's a layout of my data: Heading 1: Sub heading Sub heading Sub heading Sub heading Sub heading Heading 2: Sub heading Sub heading Sub heading Sub heading Sub heading Heading 3: Sub heading Sub heading Sub heading Sub heading Sub heading Heading 4: Sub heading Sub heading Sub heading Sub heading Sub heading Heading 5: Sub heading Sub heading Sub heading Sub heading Sub heading These headings need to have a 'Completion Status' boolean value which gets linked to a user Id. Currently, this is how my table looks: id | userID | field_1 | field_2 | field_3 | field_4 | etc... ----------------------------------------------------------------------- 1 | 1 | 0 | 0 | 1 | 0 | ----------------------------------------------------------------------- 2 | 2 | 1 | 0 | 1 | 1 | Each field represents one Sub Heading. Having this many columns in my table looks awfully inefficient... How can I go about optimizing this? I can't think of any way to neaten it up :/

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• how to 'scale' these three tables?

  - by iddqd

  I have the following Tables: Players id playerName Weapons id type otherData Weapons2Player id playersID_reference weaponsID_reference That was nice and simple. Now I need to SELECT items from the Weapons table, according to some of their characteristics that i previously just packed into the otherData column (since it was only needed on the client side). The problem is, that the types have varying characteristics - but also a lot of similar data. So I'm trying to decide on the following possibilities, all of which have their pros and cons. Solution A Kill the Weapons table, and create a new table for each Weapon-Type: Weapons_Swords id bladeType damage otherData Weapons_Guns id accuracy damage ammoType otherData But how will i Link these to the Players ? create Weapons_Swords2Players, Weapons_Guns2Players for each weapon-type? (Will result in a lot more JOINS when loading the player with all his weapons...and it's also more complicated to insert a new player) or add another column to Weapons2Players called WeaponsTypeTable, then do sub-selects to the correct Weapons sub-table (seems easier, but not really right, slightly easier insert i guess) Solution B Keep the Weapons table, and add all the fields i need to it. The Problem is that then there will be NULL fields, since not all Weapon-Types use all fields (can't be right) Weapons id type accuracy damage ammoType bladeType otherData This seems to be pretty basic stuff, but i just can't decide what's best. Or is there a correct Solution C? many thanks.

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• FIND_IN_SET exists in MySQL but how do I make it in SQLite?

  - by Pentium10

  In MySQL there exists FIND_IN_SET, that locates a match in a comma separated list. mysql> SELECT FIND_IN_SET('b','a,b,c,d'); -> 2 How would I be able to do this in SQLite in query? Please note, that I can't define or add user defined functions, the Android platform doesn't allow it.

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• LIKE operator with $variable

  - by skarama

  This is my first question here and I hope it is simple enough to get a quick answer! Basically, I have the following code: $variable = curPageURL(); $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '$variable' ; If I echo the $variable, it prints the current page's url( which is a javascript on my page) Ultimately, what I want, is to be able to make a search for which the search-term is the current page's url, with wildcards before and after. I am not sure if this is possible at all, or if I simply have a syntax error, because I get no errors, simply no result! I tried : $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '"echo $variable" ' ; But again, I'm probably missing or using a misplaced ' " ; etc. Please tell me what I'm doing wrong!

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• Java & Tomcat: SQL JDBC/JNDI Exceptions

  - by user267581

  I am deploying a webapp from eclipse to tomcat. I am having an issue with my application and JNDI lookups. When the app tries to load the JNDI resource I am this stacktrace: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused: connect] at com.sun.jndi.rmi.registry.RegistryContext.lookup(RegistryContext.java:101) at javax.naming.InitialContext.lookup(InitialContext.java:396) at org.objectweb.carol.jndi.spi.AbsContext.lookup(AbsContext.java:134) at org.objectweb.carol.jndi.spi.AbsContext.lookup(AbsContext.java:144) at javax.naming.InitialContext.lookup(InitialContext.java:392) at org.objectweb.carol.jndi.spi.MultiContext.lookup(MultiContext.java:118) at javax.naming.InitialContext.lookup(InitialContext.java:392) at com.theriabook.daoflex.JDBCConnection.getDataSource(JDBCConnection.java:61) at com.theriabook.daoflex.JDBCConnection.getConnection(JDBCConnection.java:73) at com.aramark.data.UsersDAO.doLogin(UsersDAO.java:751) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at flex.messaging.services.remoting.adapters.JavaAdapter.invoke(JavaAdapter.java:406) at flex.messaging.services.RemotingService.serviceMessage(RemotingService.java:183) at flex.messaging.MessageBroker.routeMessageToService(MessageBroker.java:1417) at flex.messaging.endpoints.AbstractEndpoint.serviceMessage(AbstractEndpoint.java:878) at com.farata.remoting.CustomAMFEndpoint.serviceMessage(CustomAMFEndpoint.java:23) at flex.messaging.endpoints.amf.MessageBrokerFilter.invoke(MessageBrokerFilter.java:121) at flex.messaging.endpoints.amf.LegacyFilter.invoke(LegacyFilter.java:158) at flex.messaging.endpoints.amf.SessionFilter.invoke(SessionFilter.java:49) at flex.messaging.endpoints.amf.BatchProcessFilter.invoke(BatchProcessFilter.java:67) at flex.messaging.endpoints.amf.SerializationFilter.invoke(SerializationFilter.java:146) at flex.messaging.endpoints.BaseHTTPEndpoint.service(BaseHTTPEndpoint.java:274) at flex.messaging.MessageBrokerServlet.service(MessageBrokerServlet.java:377) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.cti.compiler.env.web.CompilerInvocationInterceptor.doFilter(CompilerInvocationInterceptor.java:25) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447) at java.lang.Thread.run(Thread.java:619) Caused by: java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused: connect at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:601) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:198) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:184) at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:322) at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source) at com.sun.jndi.rmi.registry.RegistryContext.lookup(RegistryContext.java:97) ... 41 more Caused by: java.net.ConnectException: Connection refused: connect at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:525) at java.net.Socket.connect(Socket.java:475) at java.net.Socket.<init>(Socket.java:372) at java.net.Socket.<init>(Socket.java:186) at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:22) at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:128) at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:595) I am really stumped at this error. I am using a WinXP running on a Virtual Machine (VMWare) from a MAC. Any ideas? I have uninstalled/reinstalled tomcat multiple times.

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• How do I perform a batch insert in Django?

  - by Thierry Lam

  In mysql, you can insert multiple rows to a table in one query for n 0: INSERT INTO tbl_name (a,b,c) VALUES(1,2,3),(4,5,6),(7,8,9), ..., (n-2, n-1, n); Is there a way to achieve the above with Django queryset methods? Here's an example: values = [(1, 2, 3), (4, 5, 6), ...] for value in values: SomeModel.objects.create(first=value[0], second=value[1], third=value[2]) I believe the above is calling an insert query for each iteration of the for loop. I'm looking for a single query, is that possible in Django?

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• Select number of rows for each group where two column values makes one group

  - by Fábio Antunes

  I have a two select statements joined by UNION ALL. In the first statement a where clause gathers only rows that have been shown previously to the user. The second statement gathers all rows that haven't been shown to the user, therefore I end up with the viewed results first and non-viewed results after. Of course this could simply be achieved with the same select statement using a simple ORDER BY, however the reason for two separate selects is simple after you realize what I hope to accomplish. Consider the following structure and data. +----+------+-----+--------+------+ | id | from | to | viewed | data | +----+------+-----+--------+------+ | 1 | 1 | 10 | true | .... | | 2 | 10 | 1 | true | .... | | 3 | 1 | 10 | true | .... | | 4 | 6 | 8 | true | .... | | 5 | 1 | 10 | true | .... | | 6 | 10 | 1 | true | .... | | 7 | 8 | 6 | true | .... | | 8 | 10 | 1 | true | .... | | 9 | 6 | 8 | true | .... | | 10 | 2 | 3 | true | .... | | 11 | 1 | 10 | true | .... | | 12 | 8 | 6 | true | .... | | 13 | 10 | 1 | false | .... | | 14 | 1 | 10 | false | .... | | 15 | 6 | 8 | false | .... | | 16 | 10 | 1 | false | .... | | 17 | 8 | 6 | false | .... | | 18 | 3 | 2 | false | .... | +----+------+-----+--------+------+ Basically I wish all non viewed rows to be selected by the statement, that is accomplished by checking weather the viewed column is true or false, pretty simple and straightforward, nothing to worry here. However when it comes to the rows already viewed, meaning the column viewed is TRUE, for those records I only want 3 rows to be returned for each group. The appropriate result in this instance should be the 3 most recent rows of each group. +----+------+-----+--------+------+ | id | from | to | viewed | data | +----+------+-----+--------+------+ | 6 | 10 | 1 | true | .... | | 7 | 8 | 6 | true | .... | | 8 | 10 | 1 | true | .... | | 9 | 6 | 8 | true | .... | | 10 | 2 | 3 | true | .... | | 11 | 1 | 10 | true | .... | | 12 | 8 | 6 | true | .... | +----+------+-----+--------+------+ As you see from the ideal result set we have three groups. Therefore the desired query for the viewed results should show a maximum of 3 rows for each grouping it finds. In this case these groupings were 10 with 1 and 8 with 6, both which had three rows to be shown, while the other group 2 with 3 only had one row to be shown. Please note that where from = x and to = y, makes the same grouping as if it was from = y and to = x. Therefore considering the first grouping (10 with 1), from = 10 and to = 1 is the same group if it was from = 1 and to = 10. However there are plenty of groups in the whole table that I only wish the 3 most recent of each to be returned in the select statement, and thats my problem, I not sure how that can be accomplished in the most efficient way possible considering the table will have hundreds if not thousands of records at some point. Thanks for your help. Note: The columns id, from, to and viewed are indexed, that should help with performance. PS: I'm unsure on how to name this question exactly, if you have a better idea, be my guest and edit the title.

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• Why would I get a duplicate key error when updating a row?

  - by hdx

  I'm using postgres and I'm getting the duplicate key error when updating a row: cursor.execute("UPDATE jiveuser SET userenabled = 0 WHERE userid = %s" % str(userId)) psycopg2.IntegrityError: duplicate key value violates unique constraint "jiveuser_pk" I don't understand how updating a row can cause this error... any help will be much appreciated.

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• SSRS report combine data sources and generate csv

  - by Nithin

  I am new to ssrs. I have a report that gets data from two databases. I can create two datasets that connect to two different databases. The databases are third party and I cannot create stored procedures on the databases. My issue is that I have to combine the data from the two queries. Please help me with this issue or point me to locations where I can find answers. Thanks in advance.

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• mysql query - blog posts and comments with limit

  - by Lemon

  Hi, I have 2 tables: comments and posts and I'd like to display a list of 15 posts and maximum 2 most recent comments under each blog post the database scheme looks like this posts_table: post_id, post_txt, post_timestamp comments_table: post_id, comment_txt, comment_timestamp how the mysql query should look like to select 15 posts and related comments (max 2 most recent ones per post) ??? thanks, Leo

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• Sharepoint SSRS: Unexpected Error Encountered

  - by Nicholas

  We are running an intranet website hosted on Sharepoint 2007, serving reports to users via SSRS. Recently, our users are experiencing error when trying to access certain reports with the error message "An unexpected error has occurred". After trying many things, to cut a long story short we manage to temporarily solve the problem by manually running UPDATE STATISTICS on the tables in the database. However, this error will periodically crop up again and again, running UPDATE STATISTICS immediately solved it. I had suggested to run a daily job in the server to auto run UPDATE STATISTICS every few hours or so but was rejected by my team lead. Is there any other workaround for this error? Why does UPDATE STATISTICS solve the problem, I still not very understand?

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• How to call a scalar function in a stored procedure

  - by Luke101

  I am wacking y head over the problem with this code. DECLARE @root hierarchyid declare @lastchild hierarchyid SELECT @root = NodeHierarchyID from NodeHierarchy where ID = 1 set @lastchild = getlastchild(@root) it says it does not recognize getlastchild function. What am I doing wrong here

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