Consistent or Inconsistent FDs

Below are three functional dependencies (FDs) for attributes in the table above

For each FD:

State whether the FD is Consistent or Inconsistent with the sample data in the table above

1. StudentId → StudentName

2. StudentId, CourseCode  →  Grade

3. Grade → StudentId

1. Consistent

   We need to check each group of rows where the rows have the same X {StudentId}

   The only interesting group (the group which contains more than one row) is the group which contains the first three rows from the table

   Each time {StudentId} takes the value {862345},
   {StudentName} takes the value {David Copperfield}
   therefore the FD is consistent with the data in the table

2. Inconsistent

   We need to check each group of rows where the rows have the same X {StudentId, CourseCode}

   In the first row:
   {StudentId, CourseCode} takes the value {86234, IS3}
   {Grade} takes the value {NCN}
   In the second row:
   {StudentId, CourseCode} takes the value {86234, IS3}
   {Grade} takes the value {HD}
   therefore the FD is inconsistent with the data in the table

3. Cannot decide

   In Row 9, the determinant {Grade} has a  null value

Another Instance of STUDENT_GRADES Table

Below is a functional dependency (FD) for attributes in the table above

State whether the FD is Consistent or Inconsistent with the sample data in the table above

StudentId  →  StudentName

Inconsistent

(which is a bit of a worry)

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