To correctly represent optional participation in 1:N relationship between Advisor:Student relations where a student can have one advisor but is not required to have one and an Advisor can advice to any number of students, do the following:

Question

BlackTom AI · Accepted Answer

When modeling a 1:N relationship where each Student may have one Advisor but an Advisor can advise many Students, and having no advisor is allowed for a student, the foreign key should reside on the many side and be nullable to represent the optional participation.
Option 1: Insert AdvisorID, a PK from the Advisor relation, into the Student relation as a FK and allow it to have NULLS. This correctly places a foreign key on the Student table referencing Advisor, and the NULLs option enables students to exist without an assigned advisor, which matches the requirement of optional participation. This aligns with standard relational modeling for 1:N relationships with optional participation.
Option 2: Merge Student and Advisor relations into one relation and create a composite PK consisting of StudentID and AdvisorID. This breaks the separation of entities and would complicate queries unnecessarily; it also contradicts the typical 1:N design where Student and Advisor remain distinct entities. A composite PK here does not contribute to representing the optional participation cleanly and introduces redundancy.
Option 3: Insert StudentID, a PK from Student relation, into Advisor relation as a FK and allow NULLS. This would place a foreign key on the Advisor side, which would imply each Advisor is linked to a specific Student, effectively modeling a 1:1 or many-to-one in the opposite direction and contradicts the given 1:N orientation where many Students relate to one Advisor. It also would not capture the optional participation of the Student correctly.
Option 4: Insert AdvisorID, a PK from Advisor relation, into Student relation as a FK and set it not to permit NULLS. Requiring every Student to have an Advisor eliminates the intended optional participation, making the relationship mandatory for Students. This misrepresents the stated requirement that a student may not have an advisor.

To correctly represent optional participation in 1:N relationship between Advisor:Student relations where a student can have one advisor but is not required to have one and an Advisor can advice to any number of students, do the following: 单项选择题

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