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Er Diagram Explanation!
it has been a while since i did this level just want to make sure i got all the entities and attributes
1.we are a school we teach many coursers each has a code name and a fee
sandra and james are our best teahers we track the instructors name and phone number . we create a course and line it up with the teacher
several students cand take serveral courses . we track each student by name and phone number some dont give out their phone number
we want to tract each student enrolled in a course grade and also which teacher taught the course
OK HERE ARE MY THOUGHTS PLZ CORRECT ME IF I AM WRONG
STUDENT (studentid, studentname, phonenumber)
COURSE (courseid, coursename, teacher)
REPORT(studentidm course, grade)
TEACHER(teacherid, name, phone number, course id)
please help if i have missed anything thanks
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If a teacher's phone number changes, how many records have to be updated? For every course a teacher teaches, do you really want to record the teacher's personal info? How does a student know which courses he or she is enrolled in (is that a typo for courseid in the REPORT table)? To get a report, wouldn't you also want the term, enrollment status (withdrew, incomplete, etc.), and GPA (that means you also need to record credit hours)?
You need a lookup table for teacherid and courseid (get rid of courseid in the teacher table). The lookup (or intersection) table uses a composite primary key: teacherid and courseid.
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Originally posted by stecal
If a teacher's phone number changes, how many records have to be updated? For every course a teacher teaches, do you really want to record the teacher's personal info? How does a student know which courses he or she is enrolled in (is that a typo for courseid in the REPORT table)? To get a report, wouldn't you also want the term, enrollment status (withdrew, incomplete, etc.), and GPA (that means you also need to record credit hours)?
You need a lookup table for teacherid and courseid (get rid of courseid in the teacher table). The lookup (or intersection) table uses a composite primary key: teacherid and courseid.
thanks it was a typo in the report table should have been course id.
you have a point i am a little rusty on here
thanks
what would be a good name for a look up table?
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Originally posted by imose
what would be a good name for a look up table?
I personally wouldn't call this a "lookup table" (lookup tables, for me, associate an id with a description: e.g. FL => Florida or Fürstentum Lichtenstein - is that what DWH people call dimension tables?).
I was taught to call these "associative" entities. If you don't find they correspond to anything that has a real-life name, then M2M_TEACHER_COURSE is as good as anything.
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