2.11

Consider the advisor relation shown in the schema diagram in Figure 2.9, with s_id as the primary key of advisor. Suppose a student can have more than one advisor. Then, would s_id still be a primary key of the advisor relation? If not, what should the primary key of advisor be?

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s_id alone cannot be a primary key of the advisor relation, since it doesn’t identify uniquely a tuple in the relation advisor (It is possible for one student to have many advisors).