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  • Help to translate SQL query to Relational Algebra

    - by Mestika
    Hi everyone, I'm having some difficulties with translating some queries to Relational Algebra. I've a great book about Database Design and here is a chapter about Relational Algebra but I still seem to have some trouble creating the right one: Thoes queries I've most difficuelt with is these: SELECT COUNT( cs.student_id ) AS counter FROM course c, course_student cs WHERE c.id = cs.course_id AND c.course_name = 'Introduction to Database Design' SELECT COUNT( cs.student_id ) FROM Course c INNER JOIN course_student cs ON c.id = cs.course_id WHERE c.course_name = 'Introduction to Database Design' and SELECT COUNT( * ) FROM student JOIN grade ON student.f_name = "Andreas" AND student.l_name = "Pedersen" AND student.id = grade.student_id I know the notation can be a bit hard to paste into HTML forum, but maybe just use some common name or the Greek name. Thanks in advance Mestika

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  • Not finding field in polymorphic association with Doctrine2

    - by dimirc
    I have a polymorphic association (Class Table Inheritance) and I need use DQL to query entities of a specific child class wich can be done using "x INSTANCE OF Entity" in WHERE clause. Now I need to put conditions specific for that child class but I get this error: "Class Person has no association named student_field_1" Person = Parent Class Employee = Child class Student = Child class is there any way yo cast of somehow tell Doctrine that the Person is actually a Student and to allow me to put Student fields in the WHERE?

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  • Routing Users to single Models with Rails

    - by Eric Koslow
    I'm creating a Rails app for students and high schools and I'm having some trouble with my User.rb. I want to have a user model to be used for logging in, but having that user have many roles. The tricky part is that I want users that have a student role to have_one student page, and those that have a role of principal to have_one high_school page. The students and also nested in the high_school so the entire thing becomes a big mess. So my question(s): How do I limit a user to only creating one student / high school to represent them? Also how would I nest this student pages inside the highschool without screwing up the user system? My environment: Rails3 and Ruby 1.9.2dev Thank you!

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  • Entity Relationship Model: Ternary Relationships

    - by Ethan
    Hi, I am trying to understand why this statement in the book is wrong: "given a C entity, there is at most one related A entity and at most one related B entity". Is it that it doesn't apply to a specific kind of relationship?? So, if I have an example of a student who is in attendance to a course with a type of subject. The entities are student, attendance, course and subject. Student makes attendance in a room. Also, a student can make attendance for a subject. Does this example apply to the statement? Thanks for your time.

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  • Ruby on Rails: how to get error messages from a child resource displayed?

    - by randombits
    I'm having a difficult time understanding how to get Rails to show explicitly the error messages that a child resource is failing on when I render an XML template. Hypothetically, I have the following classes: class School < ActiveRecord::Base has_many :students validates_associated :students end class Student < ActiveRecord::Base belongs_to :school validates_format_of :email, :with => /^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i, :message => "You must supply a valid email" end Now, in the controller, let's say we want to build a trivial API to allow us to add a new School with a student in it (again, I said, it's a terrible example, but plays its role for the purpose of the question) class SchoolsController < ApplicationController def create @school = School.new @student = school.students.build @student.email = "bad@email" respond_to do |format| if @school.save # some code else format.xml { render :xml => @school.errors, :status => :unprocessable_entity } end end end end Now the validation is working just fine, things die because the email doesn't match the regex that's set in the validates_format_of method in the Student class. However the output I get is the following: <?xml version="1.0" encoding="UTF-8"?> <errors> <error>Students is invalid</error> </errors> I want the more meaningful error message that I set above with validates_format_of to show up. Meaning, I want it to say: <error>You must supply a valid email</error> What am I doing wrong for that not to show up?

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  • Search select statement

    - by Nana
    I am creating a page which would have different field for the user to search from. e.g. search by: Grade: -dropdownlist1- Student name: -dropdownlist2- Student ID: -dropdownlist3- Lessons: -dropdownlist4- Year: -dropdownlist5- How do I write the select statement for this? Each dropdownlist would need a select statement which would extract out different data from the database. But, I want to write ONE select statement which can dynamically choose the dropdownlist options. Instead of writing many many select statement. Lets say; Grade: -dropdownlist1- ; default value(all) Student name: -dropdownlist2-; default value(all) Student ID: -dropdownlist3-; 0-100 is choosen Lessons: -dropdownlist4-; A-C is choosen Year: -dropdownlist5-; 2009 is choosen

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  • how to get out information from datagridview ???

    - by ghost_j1
    hi everyone I am working on program that calculate the GBA for university student in visual c# So i make an datagridview that contain columns for each subject and its mark as later and number but after the user "student" insert his subject i want to let him to press button that get the mark and the number of the cirdit hours of each subject and calculate the GBA for the student and put the result in textbox... does anyone can help me to do it ???

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  • Ruby on Rails ActiveRecord: eager loading issue with foreign and primary key

    - by Krishnaswamy Subramanian
    The eager loading on Ruby on Rails is not working properly for the following scenario. First we had a model called marks which has the following fields id, student, subject, mark the student is a string column which has the active directory login value, later on for reporting functionality we introduce another table called user which has the following fields id, ad_name, full_name Now on the Mark model, we have added the belongs to class belongs_to :student_details, :class_name = "User", :foreign_key = "student", :primary_key = "ad_name" and when loading using the ActiveRecord's find method we are passing in the include conditon for eager loading Marks.find(:all, :include = :reserved_user) but when the find is executed, for each and every mark a student select query executed. Is this a known bug in ROR? or am i missing something?

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  • Dynamic find methods Vs conditional statements in rails

    - by piemesons
    Hello Student.find_all_by_name_and_status(‘mohit’, 1) As this will create a exception 'No method exception' first then it will be handled by dynamic Method handler and this will not Student.find(:all, :conditions => [‘name = ? and status = ?’ ‘mohit’, 1]) Does Student.find(1) Will generate method missing exception and will it prevent SQL injection?

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  • XML and XSL connection

    - by Irgat
    I have a problem between XML and XSL files. In XML file, there are some elements such as *<school><student studentID="12345"><nameStud I</name<takesCMPE471</takes<takesCMPE412</takes<takesCMPE100</takes</student<student studentID="67890"><nameStud II</name<takesCMPE471</takes<takesCMPE412</takes</student<course courseCode="CMPE471"<courseName>NAME I </courseName> <description>DESC I </description> </course><course courseCode="CMPE412"<courseName>NAME II </courseName> <description>DESC II </description> </course><course courseCode="CMPE100"<courseName>NAME III </courseName> <description>DESC III </description> </course>In XSL file,I want to reach "description" element which I specified "courseCode".Output should be like this, 1. Stud I      a. CMPE471 Desc I      b. CMPE412 Desc II     c. CMPE100 Desc III2. Stud II      a. CMPE471 Desc I     b. CMPE412 Desc II In XSL file, I tried to write something : <ol <xsl:for-each select="/school/student" <xsl:sort data-type="text" order="ascending" select="name"/ <li<xsl:value-of select="name"/ <ol type="a" <xsl:for-each select="takes" <xsl:sort data-type="text" select="text()" order="ascending"/ <li <xsl:for-each select="/school/course"//PROBLEM <xsl:value-of select="description [@courseCode = text()]"///PROBLEM </xsl:for-each//PROBLEM </li </xsl:for-each </ol </xsl:for-each </ol Thanks.

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  • calculating min and max of 2-D array in c

    - by m2010
    This program to calculate sum,min and max of array elements Max value is the problem, it is always not true. void main(void) { int degree[3][2]; int min_max[][]; int Max=min_max[0][0]; int Min=min_max[0][0]; int i,j; int sum=0; clrscr(); for(i=0;i<3;i++) { for(j=0;j<2;j++) { printf("\n enter degree of student no. %d in subject %d:",i+1,j+1); scanf("%d",&degree[i][j]); } } for(i=0;i<3;i++) { for(j=0;j<2;j++) { printf("\n Student no. %d degree in subject no. %d is %d",i+1,j+1,degree[i][j]); } } for(i=0;i<3;i++) { sum=0; for(j=0;j<2;j++) { sum+=degree[i][j]; } printf("\n sum of degrees of student no. %d is %d",i+1,sum); min_max[i][j]=sum; if(min_max[i][j] <Min) { Min=min_max[i][j]; } else if(min_max[i][j]>Max) { Max=min_max[i][j]; } } printf("\nThe minimum sum of degrees of student no. %d is %d",i,Min); printf("\nThe maximum sum of degrees of student no. %d is %d",i,Max); getch(); }

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  • How to get object properties of specific class in SPARQL

    - by udayalkonline
    hi, I have some ontology(campus.owl).There are tree classes(Student,Sport,Lecturer).Student class is joined with Lecturer class using "has" object property and Student class joined with Sport class with "isPlay" object property. problem I want to get the object property between Student and Lecturer using some SPARQL query. PREFIX rdfs: http://www.w3.org/2000/01/rdf-schema# PREFIX rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns# PREFIX my: http://www.semanticweb.org/ontologies/2010/5/Ontology1275975684120.owl# SELECT ?prop WHERE { ?prop ..........??? } Any Idea..?? Thank in advance!

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  • why wont this tester complie

    - by user1678800
    student name and id and testgrade need to compile with tester but the student class has some problem i dont know what it is and the error message is Error: Syntax error on token "(", . expected this needs to complie with the tester class to be able to run public class Student { public static void main(String[] args) { // instant varible for name, id , and test grade private String name; private int id; private int testgrade; /** * construct class * @parm String newName * @parm String newId */ public Student(String newName, int newId); { name = newName; id = newId; } /** * getName method that return instant varible name */ public String getName() { return name; } /** * getId method that return instant varible id */ public int getId() { return id; } /** * setGrade method that sets the test grade variable * * @param int grade */ public void setGrade(int grade) { testGrade = grade; } /** * getGrade method that sets test grade instance variable * * @param int grade */ public int getGrade() { return testGrade; } } }

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  • Mix Audio tracks with offset in SOX

    - by Laramie
    From ASP.Net, I am using FFMPEG to convert flv files on a Flash Media Server to wavs that I need to mix into a single MP3 file. I originally attempted this entirely with FFMPEG but eventually gave up on the mixing step because I don't believe it it possible to combine audio only tracks into a single result file. I would love to be wrong. I am now using FFMPEG to access the FLV files and extract the audio track to wav so that SOX can mix them. The problem is that I must offset one of the audio tracks by a few seconds so that they are synchronized. Each file is one half of a conversation between a student and a teacher. For example teacher.wav might need to begin 3.3 seconds after student.wav. I can only figure out how to mix the files with SOX where both tracks begin at the same time. My best attempt at this point is: ffmpeg -y -i rtmp://server/appName/instance/student.flv -ac 1 student.wav ffmpeg -y -i rtmp://server/appName/instance/teacher.flv -ac 1 teacher.wav sox -m student.wav teacher.wav combined.mp3 splice 3.3 These tools (FFMEG/SoX) were chosen based on my best research, but are not required. Any working solution would allow an ASP.Net service to input the two FMS flvs and create a combined MP3 using open-source or free tools.

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  • Symfony 1.4/ Doctrine; n-m relation data cannot be accessed in template (indexSuccess)

    - by chandimak
    I have a database with 3 tables. It's a simple n-m relationship. Student, Course and StudentHasCourse to handle n-m relationship. I post the schema.yml for reference, but it would not be really necessary. Course: connection: doctrine tableName: course columns: id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: false name: type: string(45) fixed: false unsigned: false primary: false notnull: false autoincrement: false relations: StudentHasCourse: local: id foreign: course_id type: many Student: connection: doctrine tableName: student columns: id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: false registration_details: type: string(45) fixed: false unsigned: false primary: false notnull: false autoincrement: false name: type: string(30) fixed: false unsigned: false primary: false notnull: false autoincrement: false relations: StudentHasCourse: local: id foreign: student_id type: many StudentHasCourse: connection: doctrine tableName: student_has_course columns: student_id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: false course_id: type: integer(4) fixed: false unsigned: false primary: true autoincrement: false result: type: string(1) fixed: true unsigned: false primary: false notnull: false autoincrement: false relations: Course: local: course_id foreign: id type: one Student: local: student_id foreign: id type: one Then, I get data from tables in executeIndex() from the following query. $q_info = Doctrine_Query::create() ->select('s.*, shc.*, c.*') ->from('Student s') ->leftJoin('s.StudentHasCourse shc') ->leftJoin('shc.Course c') ->where('c.id = 1'); $this->infos = $q_info->execute(); Then I access data by looping through in indexSuccess.php. But, in indexSuccess I can only access data from the table Student. <?php foreach ($infos as $info): ?> <?php echo $info->getId(); ?> <?php echo $info->getName(); ?> <?php endforeach; ?> I expected, that I could access StudentHasCourse data and Course data like the following. But, it generates an error. <?php echo $info->getStudentHasCourse()->getResult()?> <?php echo $info->getStudentHasCourse()->getCourse()->getName()?> The first statement gives a warning; Warning: call_user_func_array() expects parameter 1 to be a valid callback, class 'Doctrine_Collection' does not have a method 'getCourse' in D:\wamp\bin\php\php5.3.5\PEAR\pear\symfony\escaper\sfOutputEscaperObjectDecorator.class.php on line 64 And the second statement gives the above warning and the following error; Fatal error: Call to a member function getName() on a non-object in D:\wamp\www\sam\test_doc_1\apps\frontend\modules\registration\templates\indexSuccess.php on line 5 When I check the query from the Debug toolbar it appears as following and it gives all data I want. SELECT s.id AS s__id, s.registration_details AS s__registration_details, s.name AS s__name, s2.student_id AS s2__student_id, s2.course_id AS s2__course_id, s2.result AS s2__result, c.id AS c__id, c.name AS c__name FROM student s LEFT JOIN student_has_course s2 ON s.id = s2.student_id LEFT JOIN course c ON s2.course_id = c.id WHERE (c.id = 1) Though the question is short, as all the information mentioned it became so long. It's highly appreciated if someone can help me out to solve this. What I require is to access the data from StudentHasCourse and Course. If those data cannot be accessed by this design and this query, any other methodology is also appreciated.

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  • add Constraint on database with trigger

    - by Am1rr3zA
    Hi, I have 3 tables (Student, Course, student_course_choose(have field grade)) I defined a view on these 3 tables that get me an Average of the each student. I want to have constraint(with trigger) on these view(or on the table that need it) to limit the average of each student between 13 and 18. I somewhere read that I must use foreach statement(instead of foreach row) on trigger because when I decrease some grade of special student and his/her average become less than 13 they don't give me error (because later I increase grade of another his/her course ). how must I wrote this Trigger? (I want to implement aprh for testing trigger) note:I can write it in SQL server, oracle or Mysql no diff for me.

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  • Form dependency manager javascript

    - by user225269
    Need help in form dependency manager javascript: As you can see the checkbox below depends on either of the two criteria (the info=student or the info=all). I've come up with the code below based on this: DEPENDS ON name [BEING value] [OR name [BEING value]] CONFLICTS WITH name [BEING value] from this site: http://www.dynamicdrive.com/dynamicindex16/formdependency.htm Here's the code: <tr> <td> <input type="hidden" name="yr"> <label> <input type="checkbox" name="yr" value="year" class="DEPENDS ON info BEING student OR info BEING all"> Year</label> </td> </tr> EDIT What do I do?It doesn't work. When I change this: DEPENDS ON info BEING student Into this: DEPENDS ON info BEING student OR info BEING all The checkbox which depends on the radio button to be clicked first before it shows up. Will show up before any of the radio buttons( student, all) will be clicked.

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  • Using forward declarations for build in datatypes.

    - by bdhar
    I understand that wherever possible we shall use forward declarations instead of includes to speed up the compilation. I have a class Person like this. #pragma once #include <string> class Person { public: Person(std::string name, int age); std::string GetName(void) const; int GetAge(void) const; private: std::string _name; int _age; }; and a class Student like this #pragma once #include <string> class Person; class Student { public: Student(std::string name, int age, int level = 0); Student(const Person& person); std::string GetName(void) const; int GetAge(void) const; int GetLevel(void) const; private: std::string _name; int _age; int _level; }; In Student.h, I have a forward declaration class Person; to use Person in my conversion constructor. Fine. But I have done #include <string> to avoid compilation error while using std::string in the code. How to use forward declaration here to avoid the compilation error? Is it possible? Thanks.

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  • I am having issues with django test

    - by Mohamed
    I have this test case def test_loginin_student_control_panel(self): c = Client() c.login(username="tauri", password="gaul") response = c.get('/student/') self.assertEqual(response.status_code, 200) the view associated with the test case is this @login_required def student(request): return render_to_response('student/controlpanel.html') so my question is why the above test case redirects user to login page? should not c.login suppose to take care authenticating user?

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  • how to number t-rows ,when table generated using nested forloop in django templates

    - by stackover
    Hi, This part is from views.py results=[(A,[stuObj1,stuObj2,stuObj3]),(B,[stuObj4,stuObj5,stuObj6]),(C,[stuObj7,stuObj8])] for tup in results: total = tot+len(tup[1]) render_to_response(url,{'results':res , 'total':str(tot),}) this is template code: <th class="name">Name</th> <th class="id">Student ID</th> <th class="grade">Grade</th> {% for tup in results %} {% for student in tup|last %} {% with forloop.parentloop.counter as parentid%} {% with forloop.counter as centerid%} <tbody class="results-body"> <tr> <td>{{student.fname|lower|capfirst}} {{student.lname|lower|capfirst}}</td> <td>{{student.id}}</td> <td>{{tup|first}}</td> </tr> {% endfor %} {% endfor %} Now the problems am having are 1. numbering the rows. Here my problem is am not sure if i can do things like total=total-1 in the templates to get the numbered rows like <td>{{total}}</td> 2.applying css to tr:ever or odd. Whats happening in this case is everytime the loop is running the odd/even ordering is lost. these seems related problems. Any ideas would be great :)

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  • How can I set the name of the class xml by constructor?

    - by spderosso
    Hi, I want to be able to do something like this: @Root(name="events") class XMLEvents { @ElementList(inline=true) ArrayList<XMLEvent> events = Lists.newArrayList(); XMLEvents(){ ... events.add(new XMLEvent(time, type, professorP)); events.add(new XMLEvent(time, type, student)); events.add(new XMLEvent(time, type, course)); ... } } The XMLEvent class to go something like: class XMLEvent { @Root(name="professor") XMLEvent(DateTime time, LogType type, Professor p){ ... } @Root(name="student") XMLEvent(DateTime time, LogType type, Student st){ ... } @Root(name="course") XMLEvent(DateTime time, LogType type, Course c){ ... } } For the output to be: <events> <professor> ... </professor> <student> ... </student> <course> ... </course> </events> So depending on the constructor I call to create a new XMLEvent the root name to which is mapped is different. Is this even possible? Of course the past example was just to transmit what I need. Putting the @Root annotation there didn't change anything Thanks!

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  • Lucene Query Syntax

    - by Don
    Hi, I'm trying to use Lucene to query a domain that has the following structure Student 1-------* Attendance *---------1 Course The data in the domain is summarised below Course.name Attendance.mandatory Student.name ------------------------------------------------- cooking N Bob art Y Bob If I execute the query "courseName:cooking AND mandatory:Y" it returns Bob, because Bob is attending the cooking course, and Bob is also attending a mandatory course. However, what I really want to query for is "students attending a mandatory cooking course", which in this case would return nobody. Is it possible to formulate this as a Lucene query? I'm actually using Compass, rather than Lucene directly, so I can use either CompassQueryBuilder or Lucene's query language. For the sake of completeness, the domain classes themselves are shown below. These classes are Grails domain classes, but I'm using the standard Compass annotations and Lucene query syntax. @Searchable class Student { @SearchableProperty(accessor = 'property') String name static hasMany = [attendances: Attendance] @SearchableId(accessor = 'property') Long id @SearchableComponent Set<Attendance> getAttendances() { return attendances } } @Searchable(root = false) class Attendance { static belongsTo = [student: Student, course: Course] @SearchableProperty(accessor = 'property') String mandatory = "Y" @SearchableId(accessor = 'property') Long id @SearchableComponent Course getCourse() { return course } } @Searchable(root = false) class Course { @SearchableProperty(accessor = 'property', name = "courseName") String name @SearchableId(accessor = 'property') Long id }

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  • KODO: how set up fetch plan for bidirectional relationships?

    - by BestPractices
    Running KODO 4.2 and having an issue inefficient queries being generated by KODO. This happens when fetching an object that contains a collection where that collection has a bidrectional relationship back to the first object. Class Classroom { List<Student> _students; } Class Student { Classroom _classroom; } If we create a fetch plan to get a list of Classrooms and their corresponding Students by setting up the following fetch plan: fetchPlan.addField(Classroom.class,”_students”); This will result in two queries (get the classrooms and then get all students that are in those classrooms), which is what we would expect. However, if we include the reference back to the classroom in our fetch plan in order for the _classroom field to get populated by doing fetchPlan.addField(Student.class, “_classroom”), this will result in X number of additional queries where X is the number of students in each classroom. Can anyone explain how to fix this? KODO already has the original Classroom objects at the point that it's executing the queries to retrieve the Classroom objects and set them in each Student object's _classroom field. So I would expect KODO to simply set those objects in the _classroom field on each Student object accordingly and not go back to the database. Once again, the documentation is sorely lacking with Kodo/JDO/OpenJPA but from what I've read it should be able to do this more efficiently. Note-- EAGER_FETCH.PARALLEL is turned on and I have tried this with caching (query and data caches) turned on and off and there is no difference in the resultant queries.

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  • Need help with many-to-many relationships....

    - by yuudachi
    I have a student and faculty table. The primary key for student is studendID (SID) and faculty's primary key is facultyID, naturally. Student has an advisor column and a requested advisor column, which are foreign key to faculty. That's simple enough, right? However, now I have to throw in dates. I want to be able to view who their advisor was for a certain quarter (such as 2009 Winter) and who they had requested. The result will be a table like this: Year | Term | SID | Current | Requested ------------------------------------------------ 2009 | Winter | 860123456 | 1 | NULL 2009 | Winter | 860445566 | 3 | NULL 2009 | Winter | 860369147 | 5 | 1 And then if I feel like it, I could also go ahead and view a different year and a different term. I am not sure how these new table(s) will look like. Will there be a year table with three columns that are Fall, Spring and Winter? And what will the Fall, Spring, Winter table have? I am new to the art of tables, so this is baffling me... Also, I feel I should clarify how the site works so far now. Admin can approve student requests, and what happens is that the student's current advisor gets overwritten with their request. However, I think I should not do that anymore, right?

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