What is a Foreign Key?

1.	What is a Foreign Key?
Answer» A FOREIGN KEY comprises of single or collection of fields in a table that essentially refers to the PRIMARY KEY in another table. Foreign key CONSTRAINT ensures referential INTEGRITY in the relation between two tables. The table with the foreign key constraint is labeled as the child table, and the table CONTAINING the candidate key is labeled as the referenced or parent table. CREATE TABLE Students ( /* Create table with foreign key - Way 1 / ID INT NOT NULL Name VARCHAR(255) LibraryID INT PRIMARY KEY (ID) FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID));CREATE TABLE Students ( / Create table with foreign key - Way 2 / ID INT NOT NULL PRIMARY KEY Name VARCHAR(255) LibraryID INT FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID));ALTER TABLE Students / Add a new foreign key */ADD FOREIGN KEY (LibraryID)REFERENCES Library (LibraryID); What type of integrity constraint does the foreign key ensure? Check Write a SQL STATEMENT to add a FOREIGN KEY 'col_fk' in 'table_y' that references 'col_pk' in 'table_x'. Check

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