A database designer wants to create three tables: Supplier, Product, and Country. The Supplier table has a CountryID column with values that must appear in the Country table's CountryID column. The Product table has a ProductID column. Which table's CREATE TABLE statement(s) must specify a FOREIGN KEY?

Question

BlackTom AI · Accepted Answer

The scenario describes three tables: Supplier, Product, and Country. The constraint given is that the Supplier table has a CountryID column whose values must appear in the Country table's CountryID column, i.e., a referential integrity requirement. This establishes a relationship where Supplier references Country.

Option considerations:
- If a column in one table must match values in another table, the typical way to enforce this is to declare a FOREIGN KEY on the referencing column that points to the referenced table's primary (or candidate) key. In this case, the referring column is Supplier.CountryID and the referenced column is Country.CountryID. Therefore, the FOREIGN KEY constraint belongs on the Supplier table, linking Supplier.CountryID to Country.CountryID. This ensures that any CountryID placed in Supplier must exist in Country, enforcing the stated rule.
- The Product table has a ProductID column, which by itself is not described as referencing any other table. A FOREIGN KEY is only needed here if ProductID were intended to reference another table’s key (which is not indicated). Since the described requirement concerns Supplier.CountryID referencing Country.CountryID, Product does not require a FOREIGN KEY for this constraint.
- In general, FOREIGN KEY declarations are added to the table that contains the column performing the reference (the child or dependent table). Here, that is the Supplier table with its CountryID column referencing Country.

Therefore, the table that must specify a FOREIGN KEY is the one that contains the referencing column (Supplier.CountryID), ensuring the values exist in the Country table.

类似问题

Following are the definitions of 2 tables in a DBMS: EMPLOYEE(EmpID,FirstName,LastName,PositionID,Salary) POSITION(PositionID,PositionName,DeptID,EmplID) What is the foreign key in the Table EMPLOYEE?

Question 15

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