I want to check for records that have the same data as other records in case a mistake was made during data upload.  I want something like a self-join in SQL:  SELECT Id FROM My_Object__c a, My_Object__c WHERE a.Start_Date = b.Start_Date AND a.Student_Number = b.Student_Number AND a.Id != b.Id   Or  SELECT Id FROM My_Object__c WHERE Start_Date IN (SELECT Start_Date FROM Enrolment_c)   However, these give errors.  SELECT COUNT(Id), Student_Number__c, Study_start__c FROM Enrolment__c GROUP BY Study_Start__c, Student_Number__c ORDER BY COUNT(Id) DESC LIMIT 10   Gives Line: 1, Column: 1 System.UnexpectedException: field 'Student_Number__c' can not be grouped in a query call  Note that I cannot use GROUP BY as some of my fields such as Student_Number are not groupable.
I have a large amount of duplicate records (25.000) in an even larger table (250.000 records). I've done the detection using the reporting function. The criteria I used to detect the duplicates were 3 fields (unique account identifier, unique user identifier and date). Based on a list of criteria, I would like to either merge or delete these records. I've got a handle on the logic associated with the merging and the deleting but what I'm having trouble with is defining the duplicate detection process.   I'm looking at either creating a custom object to take care of the detection or dumping the records into an SQL database and taking care of it offline. Any thoughts on which one of the two is the best approach?  Edit:  After reading the first comment, I think the more appropriate question would be "How do I approach the problem in SOQL".  The object I'm working with is the Event object and I'm really only looking at the standard fields, AccountId, OwnerId and ActivityDate. From what I've found online, there's no easy way to find records that have the same value for these three fields. I think it could be accomplished by nesting SOQL queries but I'd like to use a different approach if at all possible.
Sequence of triangles with exponentiated sides Let $a,b,c\in\Bbb R^+$. For any given $n\in\Bbb N$ there exists a triangle with sides $a^n,b^n,c^n$. Show that at least two of $a,b,c$ are equal.   I know that you can create inequalities for $a^n,b^n,c^n$, but what's next? $f$ be a smooth function on real line , $f(0)=0$ , $f(x)>0, \forall x \ne 0$ and any $f^{(n)}(0)=0$ ; is $\sqrt f$ smooth? Let $f: \mathbb R \to \mathbb R$ be an infinitely differentiable function such that $f(0)=0$ , $f(x)&gt;0 , \forall x \ne 0$ and   $f^{(n)}(0)=0$ ( the $n$-th derivative ) $,  \forall n \in \mathbb N$ , then is the function $g(x):=\sqrt{f(x)}$ infinitely   differentiable ? I am having difficulty checking whether any $n$-th derivative exist at $0$ . Please help . Thanks in advance Is the "the ... the ..." construction governed by some grammatical rule? Reese's boyfriend seems to constantly be asleep. When I try and talk to him, she warns me that he's been hard at work all night, but I can't actually enter the shop at night.   Is there any way to talk to him or any benefit for doing so? I've tried to talk to him daily for a week (thinking it was something akin to talking to Sable) but I've had no luck. Trying to come in after-hours doesn't work. Search with Auto-Complete (like Gmail / Intellisense) I'm trying to solve    So far I've done the first part, evaluating the summation ;  where a is just n. I'm not sure where to go from here or what it even means deduce the second summation. I understand that the summation of simply $$\sum\limits_{k=0}^n\cos(kx)$$ is derived from looking at the real part of  $$\sum_{k=0}^n{\rm e}^{ikx} $$I'm guessing they want me to see how the second summation in the question is defined by 'playing around' with the original? When starring a message from the star board, it's not reflected in the main chat window If you click to star a post on the side (in the starred list), it changes color but not the star by the main chat area (it does add one to the number, but it doesn't change the color). Then when you click the star on the main chat area, it changes color to yellow but lowers the number by one  After clicking in sidebar:     After clicking in the main chat: What is the physical meaning of commutators in quantum mechanics? This is a question I've been asked several times by students and I tend to have a hard time phrasing it in terms they can understand. This is a natural question to ask and it is not usually well covered in textbooks, so I would like to know of various perspectives and explanations that I can use when teaching.  The question comes up naturally in what is usually students' second course in quantum physics / quantum mechanics. At that stage one is fairly comfortable with the concept of wavefunctions and with the Schrödinger equation, and has had some limited exposure to operators. One common case, for example, is to explain that some operators commute and that this means the corresponding observables are 'compatible' and that there exists a mutual eigenbasis; the commutation relation is usually expressed as $[A,B]=0$ but no more is said about that object.  This naturally leaves students wondering     what is, exactly, the physical significance of the object $[A,B]$ itself?   and this is not an easy question. I would like answers to address this directly, ideally at a variety of levels of abstraction and required background. Note also that I'm much more interested in the object $[A,B]$ itself than what the consequences and interpretations are when it is zero, as those are far easier and explored in much more depth in most resources.    One reason this is a hard question (and that commutators are such confusing objects for students) is that they serve a variety of purposes, with only thin connecting threads between them (at least as seen from the bottom-up perspective).   Commutation relations are usually expressed in the form $[A,B]=0$ even though, a priori, there appears to be little motivation for the introduction of such terminology. A lot of stock is placed behind the canonical commutation relation $[x,p]=i \hbar$, though it is not always clear what it means.  (In my view, the fundamental principle that this encodes is essentially de Broglie's relation $\lambda=h/p$; this is made rigorous by the  but that's quite a bit to expect a student to grasp at a first go.) From this there is a natural extension to the Heisenberg Uncertainty Principle, which in its general form includes a commutator (and an anticommutator, to make things worse). Canonically-conjugate pairs of observables are often introduced, and this is often aided by observations on commutators. (On the other hand, the energy-time and angle-angular momentum conjugacy relations cannot be expressed in terms of commutators, making things even fuzzier.) Commutators are used very frequently, for example, when studying the angular momentum algebra of quantum mechanics. It is clear they play a big role in encoding symmetries in quantum mechanics but it is hardly made clear how and why, and particularly why the combination $AB-BA$ should be important for symmetry considerations.  This becomes even more important in more rigorous treatments of quantum mechanics, where the specifics of the Hilbert space become less important and the algebra of observable operators takes centre stage. The commutator is the central operation of that algebra, but again it's not very clear why that combination should be special. An analogy is occasionally made to the Poisson brackets of hamiltonian mechanics, but this hardly helps - Poisson brackets are equally mysterious. This also ties the commutator in with time evolution, both on the classical side and via the Heisenberg equation of motion.   I can't think of any more at the moment but they are a huge number of opposing directions which can make everything very confusing, and there is rarely a uniting thread. So: what are commutators, exactly, and why are they so important? How do I get query string value from script path? How many squares on a 5-foot grid does a 5-foot radius spell affect? We had a situation come up regarding this term and how it affected spells.  In the spell Moonbeam, for example, it says a 5-foot radius cylinder appears. Does this mean that from the center of square it extends 2.5 feet into the next square hypothetically hitting up three squares or does this mean from the edge of one the target square to the five feet and five feet the other direction effectively covering only two squares for a total of 10 feet between total range of both squares?  I understand that radius means half the distance of a circle from the center point. The spell is not the issue but the understanding of radius as it pertains to the spell, as there are other spells that are worded similarly such as Fireball, etc.  Essentially we are asking, does the spell in the example effect one square or three? This would be saying the edge of the initial square is the point of origin and not the center of the square for the total distance of ten feet.  I had been working under the understanding that the radius is half of the distance and therefore dragging a ruler from the center of where I want the spell to take effect would get me the area of effect.  It's much easier to do this with Fireball, due to the larger area to effect, but this one has such a small area and therefore sparked the debate. We are using a grid system to mark the distance, etc. We play within the digital realm of roll20.com. Can't boot Windows 7 after installing Ubuntu I installed Ubuntu yesterday alongside Windows 7 and whenever I start my computer I don't have the option to boot Windows. When the computer starts it goes straight to Ubuntu without giving me an OS selection menu. When it goes to Ubuntu it gives me Ubuntu repair options and Ubuntu normal start option. I still have all of the Windows 7 files on my hard drive, but Windows 7 has no way to boot. Wavy stream of liquid I built a model of multiple linear regression to predict the revenues at the box office of a movie: the variable $Y$ is revenue while the variables $X$ are two: Activity (number of tweets per day) and sentiment (connotation of these tweets).  The problem is that the intercept is not significant. I thought of a possible explanation: the intercept in practice is the value of the variable $Y$ when the variables $X$ assume values of 0; but because of the very strong development of social networks, it is virtually impossible not to have even a tweet (and then a wave of activity) about a movie that just came out, I thought that the significance or not the intercept could be neglected because the assumed value has no meaning in reality (a tweet of 0 would never be satisfied, given the market today). In this way, I consider the intercept a mere constant for the calculation of the line, without worrying about its significance (because in some cases would take negative values, which is impossible for revenues).  The interpretation may be correct? I was able to read and write NTFS filesystems normally in Mountain Lion, but after the upgrade this stopped to work.  I installed ntfs-3g and fuse4x using homebrew in Mountain Lion and followed the instructions displayed by homebrew to finish the installation of fuse4x kernel extension.  To try to solve this problem I removed ntfs-3g, fuse4x and fuse4x-kext and reinstalled them. But this didn't solve my problem.  Does anyone know how to solve this? Thanks. How do I create an Excel (.XLS and .XLSX) file in C# without installing Microsoft Office? How can I create an Excel spreadsheet with C# without requiring Excel to be installed on the machine that's running the code? Fire (at, on, in, to) target How to correctly choose the preposition in "fire (at, on, in, to) target"? There's a way to fill with faces only the area between the larger circle and the the smaller one? I mean.. It's a wheel and I'm trying to fill the rubber part of it.  Using the fill function F it fills everything inside the bigger circle. Finding the Public IP address in a shell script I can find my IP address using ifconfig or hostname -i command.  But how do I find my Public IP?  (I have a static public IP but I want to find it out using unix command) Centering with \includegraphics not with \begin{figure}? I mess up with things when I try to use the figure-thing: the picture is not appearing with the correct alignment (apparently because I forget the float package). Now I want to use only the graphicx package with \includegraphics. How can I center the \includegraphics without figure?  Not working or doing centering to the document afterwards.  \includegraphics[width=0.5 \textwidth]{./Pictures/r.png}{\centering} \includegraphics[width=0.5 \textwidth]{./Pictures/r.png}\centering Can you quickly tell me if this pseudocode makes sense or not?