A database designer wants to create three tables: Supplier, Product, and Country. The Supplier table has a Countryld column with values that must appear in the Country table's Countryld column. The Product table has an auto-increment column. Which table's CREATE TABLE statement(s) must specify a FOREIGN KEY?
a. Supplier
b. Product
c. Country
d. Supplier and Country

(a) Supplier

Explanation:

In database design, two tables are linked together using a FOREIGN KEY. A foreign key is formed from one or more columns of one table that reference or match another key (often called a primary key) in another table. In other words, when a column or a combination of columns on one table points to a primary key of another table, the column(s) will specify the foreign key.

PS: A primary key is used to make each entry of a table unique.

In the given tables - Supplier, Product, Country -  since the Supplier table has a column called CountryId referencing the CountryId column of the Country table, then CountryId is a primary key in Country table but a foreign key in Supplier table.

Therefore, the CREATE TABLE statement(s) of the Supplier table must specify a foreign key.

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