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• Repeating fields in similar database tables

  - by user1738833

  I have been tasked with working on a database that I have never seen before and I'm looking at the DB structure. Some of the central and most heavily queried and joined tables look like virtual duplicates of each other. Here's a massively simplified representation of the situation, with business-sensitive information changed, listing hypothetical table names and fields: TopLevelGroup: PK_TLGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK SubGroup: PK_SubGroupId, FK_ParentTopLevelGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK SubSubGroup: PK_SubSUbGroupId, FK_ParentSubGroupId, DisplaysXOnBill, DisplaysYOnBill, IsInvoicedForJ, IsInvoicedForK I haven't listed the types of the fields as I don't think it's particularly important to the situation. In addition, it's worth saying that rather than four repeated fields as in the example above, I'm looking at 86 repeated fields. For the most part, those fields genuinely do represent "facts" about the primary table entity, so it's not automatically wrong for that reason. In addition, the "groups" represented here have a property inheritance relationship. If DisplaysXOnBill is NULL in the SubSubGroup, it takes the value of DisplaysXOnBillfrom it's parent, the SubGroup, and so-on up to the TopLevelGroup. Further, the requirements will never require that the model extends beyond three levels, so there is no need for flexibility in that area. Is there a design smell from several tables which describe very similar entities having almost identical fields? If so, what might be a better design of the example above? I'm using the phrase "design smell" to indicate a possible problem. Of course, in any given situation, a particular design might well be the best solution. I'm looking for a more general answer - wondering what might be wrong with this design and what might be the better design were that the case. Possibly related, but not primary questions: Is this database schema in a reasonably normal form (e.g. to 3NF), insofar as can be told from the information I've provided. I can't see a problem with the requirements of 2NF and 3NF, except in their inheriting the requirements of 1NF. Is 1NF satisfied though? Are repeating groups allowed in different tables? Is there a best-practice method for implementing the inheritance relationship in a database as I require? The method above feels clunky to me because any query on the SubSubGroup necessarily needs to join onto the SubGroup and the TopLevelGroup tables to collect inherited facts, which can make even trivial joins requiring facts from the SubSubGroup table rather long-winded. There are, of course, political considerations to making a relatively large change like this. For the purpose of this question, I'm happy to ignore that fact in the interests of keeping the answers ring-fenced to the technical problem.

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• How do I map common properties in NHibernate

  - by Ian Oakes

  In the database I'm working with, every table repeats the same nine columns and I don't want to have to supply the same properties in each of my entities to map these columns. I've tried adding properties to a common base class and adding them to the sub class's mapping file, but this doesn't work. I've read the documentation around inheritance mapping but this did not help. What is the best way to map columns that repeat accross multiple tables in NHibernate?

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• A good free BON diagram generator?

  - by Audel

  Hello I need to create a static BON diagram which represents a set of clusters, classes and their relationships(inheritance and client-supplier). Does anyone know a good diagram generator I can get for free? The BON diagram is similar to the C sharp's class diagram but this one is generated by Eiffel studio =/ any diagram generators recommendations are welcome ;D Thanks in advance .

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• Naming multi-instance performance counters in .NET

  - by Roger Lipscombe

  Most multiple instance performance counters in Windows seem to automatically(?) have a #n on the end if there's more than one instance with the same name. For example: if, in Perfmon, you look under the Process category, you'll see: ... dwm explorer explorer#1 ... I have two explorer.exe processes, so the second counter has #1 appended to its name. When I attempt to do this in a .NET application: I can create the category, and register the instance (using the PerformanceCounterCategory.Create that takes a CounterCreationDataCollection). I can open the counter for write and write to it. When I open the counter a second time, it opens the same counter. This means that I have two applications fighting over the counters. The documentation for PerformanceCounter.InstanceName states that # is not allowed in the name. So: how do I have multiple-instance performance counters that are actually multiple instance? And where the second (and subsequent) instances get #n appended to the name? That is: I know that I can put the process ID (e.g.) on the instance name. This works, but has the unfortunate side effect that restarting the process results in a new PID, and Perfmon continues monitoring the old counter.

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• Partial Classes - are they bad design?

  - by dferraro

  Hello, I'm wondering why the 'partial class' concept even exists in .NET. I'm working on an application and we are reading a (actually very good) book relavant to the development platform we are implementing at work. In the book he provides a large code base /wrapper around the platform API and explains how he developed it as he teaches different topics about the platform development. Anyway, long story short - he uses partial classes, all over the place, as a way to fake multiple inheritence in C# (IMO). Why he didnt just split the classes up into multiple ones and use composition is beyond me. He will have 3 'partial class' files to make up his base class, each w/ 3-500 lines of code... And does this several times in his API. Do you find this justifiable? If it were me, I'd have followed the S.R.P. and created multiple classes to handle different required behaviors, then create a base class that has instances of these classes as members (e.g. composition). Why did MS even put partial class into the framework?? They removed the ability to expand/collapse all code at each scope level in C# (this was allowed in C++) because it was obviously just allowing bad habits - partial class is IMO the same thing. I guess my quetion is: Can you explain to me when there would be a legitimate reason to ever use a partial class? I do not mean this to be a rant / war thread. I'm honeslty looking to learn something here. Thanks

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• Java - Virtual Methods

  - by Gogi

  How does virtual functions work behind the scenes in Inheritance ? Does the compiler treat virtual functions specially ?

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• What is the minimum interface that has the Count property in .Net

  - by SoMoS

  Hello, I need to change a method that has one parameter that takes a serie of objects. I need to find the lowest Interface (in inheritance tree) that has the Count property. Until now I was using the IEnumerable but as this has not Count I need to change it to the wider interface possible so the method can work with the biggest number of types of series (collections, lists, arrays, etc). Thanks in advance.

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• Java Virtual Machine Internals

  - by giolekva

  Hey, Can u suggest some articles or books about JVM internals: how it allocates memory, handles object inheritance, garbage collection, how it executes byte code and so on.

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• Many to many table design question

  - by user169867

  Originally I had 2 tables in my DB, [Property] and [Employee]. Each employee can have 1 "Home Property" so the employee table has a HomePropertyID FK field to Property. Later I needed to model the situation where despite having only 1 "Home Property" the employee did work at or cover for multiple properties. So I created an [Employee2Property] table that has EmployeeID and PropertyID FK fields to model this many 2 many relationship. Now I find that I need to create other many-to-many relationships between employees and properties. For example if there are multiple employees that are managers for a property or multiple employees that perform maintenance work at a property, etc. My questions are: 1) Should I create seperate many-to-many tables for each of these situations or should I just create 1 more table like [PropertyAssociatonType] that lists the types of associations an emploee can have with a property and just add a FK field to [Employee2Property] such a PropertyAssociationTypeID that explains what the association is? I'm curious about the pros/cons or if there's another better way. 2) Am I stupid and going about this all worng? Thanks for any suggestions :)

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• Merge Multple Worksheets From Multple Workbooks

  - by Droter

  Hi, I have found multiple posts on merging data but I am still running into some problems. I have multiple files with multiple sheets. Example 2007-01.xls...2007-12.xls in each of these files are daily data on sheets labeled 01, 02, 03 ..... There are other sheets in the file so I can't just loop through all worksheets. I need to combine the daily data into monthly data, then all of the monthly data points into yearly. On the monthly data I need it to be added to the bottom of the page. I have added the file open changes for Excel 2007 Here is what I have so far: Sub RunCodeOnAllXLSFiles() Dim lCount As Long Dim wbResults As Workbook Dim wbMaster As Workbook Application. ScreenUpdating = False Application.DisplayAlerts = False Application.EnableEvents = False On Error Resume Next Set wbMaster = ThisWorkbook Dim oWbk As Workbook Dim sFil As String Dim sPath As String sPath = "C:\Users\test\" 'location of files ChDir sPath sFil = Dir("*.xls") 'change or add formats Do While sFil <> "" 'will start LOOP until all files in folder sPath have been looped through Set oWbk = Workbooks.Open(sPath & "\" & sFil) 'opens the file Set oWbk = Workbooks.Open(sPath & "\" & sFil) Sheets("01").Select ' HARD CODED FIRST DAY Range("B6:F101").Select 'AREA I NEED TO COPY Range("B6:F101").Copy wbMaster.Activate Workbooks("wbMaster").ActiveSheet.Range("B65536").End(xlUp)(2).PasteSpecial Paste:=xlValues Application.CutCopyMode = False oWbk.Close True 'close the workbook, saving changes sFil = Dir Loop ' End of LOOP On Error Goto 0 Application.ScreenUpdating = True Application.DisplayAlerts = True Application.EnableEvents = True End Sub Right now it can find the files and open them up and get to the right worksheet but when it tries to copy the data nothing is copied over. Thanks for your help, Matt

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• Writing SDK documentation, need useful beginner tutorials

  - by David Rutten

  I'm currently writing SDK documentation for one of our products, but for obvious reasons I don't want to talk about the essentials of OOP. Does anyone know any good online teaching material that explain (aimed at absolute beginners) concepts such as classes, inheritance, constructors, instances etc.? Preferably urls that are likely to survive for a couple of years to come... It's a DotNET SDK and we're including only VB and C# samples, so C++ or Delphi or Lisp material is not that useful.

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• What features would you like to see removed from C++?

  - by Justin Ethier

  This question was inspired by what-features-would-you-like-to-see-added-to-c. anBasically, C++ is a great general-purpose language. But perhaps too general and feature-rich... multiple inheritance, operator overloading, manual memory management, templates, smart pointers, virtual destructors, legacy frameworks (think MFC), and I could just go on. Is there any one feature / aspect of C++ that you would like taken away, to make our lives easier as C++ developers? One feature per answer, please.

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• Adapter for circle page indicator in android

  - by Charles LAU

  I am currently working on an android application which have multiple pages. I am trying to use Circle page indicator to allow users view multiple pages by flipping over the screen. Each page has seperate XML file for the view and each page has a button which is bind to a java method in the Activity. I would like to know how to initalise all the buttons in the Activity for multiple pages. Because at the moment, I can only initalise the button for the first page of the views. I cannot initalise the button for second and third page. Does anyone know how to achieve this. I have placed all the jobs to be done for all the buttons in a single activity. I am currently using this indicator : http://viewpagerindicator.com/ Here is my adapter for the circle page indicator: @Override public Object instantiateItem(View collection, int position) { inflater = (LayoutInflater) collection.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); int resid = 0; //View v = null;// inflater.inflate( R.layout.gaugescreen, (ViewPager)collection, false ); switch( position ) { case 0: resid = R.layout.gaugescreen; break; case 1: resid= R.layout.liveworkoutstatisticsscreen; break; case 2: resid = R.layout.mapscreen; break; default: resid = R.layout.gaugescreen; break; } View view = inflater.inflate(resid, null); ((ViewPager) collection).addView(view,0); return view; } Does anyone know how to achieve this? Thanks for any help in advance

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• C# - calling ext. DLL function containing Delphi "variant record" parameter

  - by CaldonCZE

  Hello, In external (Delphi-created) DLL I've got the following function that I need to call from C# application. function ReadMsg(handle: longword; var Msg: TRxMsg): longword; stdcall; external 'MyDll.dll' name 'ReadMsg'; The "TRxMsg" type is variant record, defined as follows: TRxMsg = record case TypeMsg: byte of 1: (accept, mask: longword); 2: (SN: string[6]); 3: (rx_rate, tx_rate: word); 4: (rx_status, tx_status, ctl0, ctl1, rflg: byte); end; In order to call the function from C#, I declared auxiliary structure "my9Bytes" containing array of bytes and defined that it should be marshalled as 9 bytes long array (which is exactly the size of the Delphi record). private struct my9Bytes { [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 9)] public byte[] data; } Then I declared the imported "ReadMsg" function, using the "my9bytes" struct. [DllImport("MyDll.dll")] private static extern uint ReadMsg(uint handle, ref my9Bytes myMsg); I can call the function with no problem... Then I need to create structure corresponding to the original "TRxMsg" variant record and convert my auxiliary "myMsg" array into this structure. I don't know any C# equivalent of Delphi variant array, so I used inheritance and created the following classes. public abstract class TRxMsg { public byte typeMsg; } public class TRxMsgAcceptMask:TRxMsg { public uint accept, mask; //... } public class TRxMsgSN:TRxMsg { public string SN; //... } public class TRxMsgMRate:TRxMsg { public ushort rx_rate, tx_rate; //... } public class TRxMsgStatus:TRxMsg { public byte rx_status, tx_status, ctl0, ctl1, rflg; //... } Finally I create the appropriate object and initialize it with values manually converted from "myMsg" array (I used BitConverter for this). This does work fine, this solution seems to me a little too complicated, and that it should be possible to do this somehow more directly, without the auxiliary "my9bytes" structures or the inheritance and manual converting of individual values. So I'd like to ask you for a suggestions for the best way to do this. Thanks a lot!

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• Django repeating vars/cache issue?

  - by Mark

  I'm trying to build a better/more powerful form class for Django. It's working well, except for these sub-forms. Actually, it works perfectly right after I re-start apache, but after I refresh the page a few times, my HTML output starts to look like this: <input class="text" type="text" id="pickup_addr-pickup_addr-pickup_addr-id-pickup_addr-venue" value="" name="pickup_addr-pickup_addr-pickup_addr-pickup_addr-venue" /> The pickup_addr- part starts repeating many times. I was looking for loops around the prefix code that might have cause this to happen, but the output isn't even consistent when I refresh the page, so I think something is getting cached somewhere, but I can't even imagine how that's possible. The prefix car should be reset when the class is initialized, no? Unless it's somehow not initializing something? class Form(object): count = 0 def __init__(self, data={}, prefix='', action='', id=None, multiple=False): self.fields = {} self.subforms = {} self.data = {} self.action = action self.id = fnn(id, 'form%d' % Form.count) self.errors = [] self.valid = True if not empty(prefix) and prefix[-1:] not in ('-','_'): prefix += '-' for name, field in inspect.getmembers(self, lambda m: isinstance(m, Field)): if name[:2] == '__': continue field_name = fnn(field.name, name) field.label = fnn(field.label, humanize(field_name)) field.name = field.widget.name = prefix + field_name + ife(multiple, '[]') field.id = field.auto_id = field.widget.id = ife(field.id==None, 'id-') + prefix + fnn(field.id, field_name) + ife(multiple, Form.count) field.errors = [] val = fnn(field.widget.get_value(data), field.default) if isinstance(val, basestring): try: val = field.coerce(field.format(val)) except Exception, err: self.valid = False field.errors.append(escape_html(err)) field.val = self.data[name] = field.widget.val = val for rule in field.rules: rule.fields = self.fields rule.val = field.val rule.name = field.name self.fields[name] = field for name, form in inspect.getmembers(self, lambda m: ispropersubclass(m, Form)): if name[:2] == '__': continue self.subforms[name] = self.__dict__[name] = form(data=data, prefix='%s%s-' % (prefix, name)) Form.count += 1 Let me know if you need more code... I know it's a lot, but I just can't figure out what's causing this!

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• How to query an Entity Framework entities container for objects of derived entity classes?

  - by Ivan

  I have a complex inheritance structure in my data model. A majority of classes in my model (which is designed in VS 2010 with a DB generated by it after) are derived from 3 basic classes. And only these 3 classes can be found among the context members. How do I use all the derived classes at all?

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• Did Java invent interfaces?

  - by Jordão

  I know about C++ pure virtual classes, but Java went one step further and created a first-class (no pun intended) concept for multiple-interface (not implementation) inheritance, the interface. It's now a staple of major statically-typed languages. Did Java invent the interface concept? Or did it appear in older languages also as a first-class concept?

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• Iterating Over <select> Using jQuery + Multi Select

  - by Kezzer

  This isn't quite as straight forward as one may think. I'm using a plugin called jQuery MultiSelect and multiple <select options using XSLT as follows: <xsl:for-each select="RootField"> <select id="{RootField}" multiple="multiple" size="3"> <option value=""></option> <xsl:for-each select="ChildField"> <option value="{ChildField}"><xsl:value-of select="ChildField"/></option> </xsl:for-each> </select> </xsl:for-each> The accompanying JavaScript is as follows: var selects = document.getElementsByTagName("select"); $.each(selects, function() { $(this).multiSelect(); }); This allows me to apply the multiSelect(); function to every single <select on the page. The behaviour is quite strange, every other <select is being changed into the dropdown list (all the even ones anyway). I can't see anything wrong in my JavaScript to cause this issue as it would iterate over every single one. To make it more clear, the only lists that have that JavaScript applied to it are ones in position 2, 4, 6 and 8 (out of the 9 which are on the page). Any ideas?

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• Thread Safety of C# List<T> for readers

  - by ILIA BROUDNO

  I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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• Table per Type Inhertiance and Data Genertion Plans

  - by CodeGrue

  I have an Entity Framework model using Table per Type Inheritance, but when I use a VS Data Generation Plan it produces duplicate keys in the child tables, which is a problem for EF. Does anyone know of a way to get this to work, so that the child tables do not have overlapping keys?

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• Why are static classes considered “classes” and “reference types”?

  - by Timwi

  I’ve been pondering about the C# and CIL type system today and I’ve started to wonder why static classes are considered classes. There are many ways in which they are not really classes: A “normal” class can contain non-static members, a static class can’t. In this respect, a class is more similar to a struct than it is to a static class, and yet structs have a separate name. You can have a reference to an instance of a “normal” class, but not a static class (despite it being considered a “reference type”). In this respect, a class is more similar to an interface than it is to a static class, and yet interfaces have a separate name. The name of a static class can never be used in any place where a type name would normally fit: you can’t declare a variable of this type, you can’t use it as a base type, and you can’t use it as a generic type parameter. In this respect, static classes are somewhat more like namespaces. A “normal” class can implement interfaces. Once again, that makes classes more similar to structs than to static classes. A “normal” class can inherit from another class. It is also bizarre that static classes are considered to derive from System.Object. Although this allows them to “inherit” the static methods Equals and ReferenceEquals, the purpose of that inheritance is questionable as you would call those methods on object anyway. C# even allows you to specify that useless inheritance explicitly on static classes, but not on interfaces or structs, where the implicit derivation from object and System.ValueType, respectively, actually has a purpose. Regarding the subset-of-features argument: Static classes have a subset of the features of classes, but they also have a subset of the features of structs. All of the things that make a class distinct from the other kinds of type, do not seem to apply to static classes. Regarding the typeof argument: Making a static class into a new and different kind of type does not preclude it from being used in typeof. Given the sheer oddity of static classes, and the scarcity of similarities between them and “normal” classes, shouldn’t they have been made into a separate kind of type instead of a special kind of class?

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• Named previously unnamed branch

  - by Jab

  It seems naming a previously unnamed branch doesn't really work out. It creates a nasty multiple heads problem that I can't find a solution for. Here is the workflow... UserA starts working on feature that they expect to be small, so they just start working(off the default branch). The change turns out to be a large project and will need multiple contributors. So UserA issues... hg branch "Feature1" and continues working, committing locally s needed. UserA then pulls down the changes from the central repo so he can push. At this point, why does hg heads return 3 heads? It shows 2 for default and 1 for Feature1. The first head for default is the latest change by another user on the branch(irrelevant). The second default head is the commit prior to the hg branch "Feature1" commit. The central repository has rules enforced so that only 1 head per branch is allowed, so forcing a push isn't an option. The repo doesn't want multiple heads on the default branch. UserA should be able to push these changes so that other users can see the Feature1 branch and help out. I can't seem to find a way to "correct" this. I don't think I can re-write the branch of the initial commits for the feature, before it was a named branch. I know the initial changes before the named branch are technically on the default branch, but does that mean they will be heads until that Feature1 branch is merged?

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• Why does nothing in WPF have a click event?

  - by Shane

  This seems very strange to me. I know through some adventurous inheritance you can convert most UIElements to a button, but it is a cumbersome way of implementing the most basic of of computer events

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• Codeigniter Inserting Multidimensional Array as rows in MySQL

  - by RisingSun

  Please Refer to this question I asked Codeigniter Insert Multiple Rows in SQL To restate <tr> <td><input type="text" name="user[0][name]" value=""></td> <td><input type="text" name="user[0][address]" value=""><br></td> <td><input type="text" name="user[0][age]" value=""></td> <td><input type="text" name="user[0][email]" value=""></td> </tr> <tr> <td><input type="text" name="user[1][name]" value=""></td> <td><input type="text" name="user[1][address]" value=""><br></td> <td><input type="text" name="user[1][age]" value=""></td> <td><input type="text" name="user[1][email]" value=""></td> </tr> .......... Can Be Inserted into MySQL as this foreach($_POST['user'] as $user) { $this->db->insert('mytable', $user); } This results in multiple MySQL queries. Is it possible to optimise it further, so that the insert occurs in one query Something like this insert multiple rows via a php array into mysql but taking advantage of codeigniters simpler syntax. Thanks

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• Database design - table relationship question

  - by iama

  I am designing schema for a simple quiz application. It has 2 tables - "Question" and "Answer Choices". Question table has 'question ID', 'question text' and 'answer id' columns. "Answer Choices" table has 'question ID', 'answer ID' and 'answer text' columns. With this simple schema it is obvious that a question can have multiple answer choices & hence the need for the answer choices table. However, a question can have only one correct answer and hence the need for the 'answer ID' in the question table. However, this 'answer ID' column in the question table provides a illusion as though there can be multiple questions for a single answer which is not correct. The other alternative to eliminate this illusion is to have another table just for correct answer that will have just 2 columns namely the question ID and the answer ID with a 1-1 relationship between the two tables. However, I think this is redundant. Any recommendation on how best to design this thereby enforcing the rules that a question can have multiple answer choices but only one correct answer? Many Thanks.

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