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Give an example of 3 relations illustrating primary keys and foreign keys f 3 relations illustrating primary keys and foreign keys Use your example for a simple Relational algebra query

Answer 1

Solution: Basic concepts about primary Key and foreign key: Primary key is the key used to identify the records in a relation uniquely The primary key should not be null and it should be unique for a particular entry The foreign keys are used to refer other relation entries .To refer content uniquely from another table that content should be unique in that table to avoid conflicts, thus foreign key reference should be a primary key of the referencing table Example of 3 relations: 1)Relation Customer TABLE Customer CustomerID int NOT NULL Name varchar (20) Phone varchar (10) PRIMARY KEY (CustomerID) ii) Relation Order: TABLE Order OrderID int NOT NULL ItemID int Quantity int, CustomerID int Total int, PRIMARY KEY (OrderID) FOREIGN KEY (CustomerID) FOREIGN KEY(ItemID), iii)Relation Item:

TABLE Item ItemID int NOT NULL, ItemName varChar, Price int, PRIMARY KEY (ItemID), In above relations, the relation "Order" has "OrderID" as foreign keys, we can notice that the foreign keys are primary keys of other relations primary key, "ItemID" and "CustomerID" as A rellatdiopm.al allorelbora ƠItemID '1234' (orders) = .The above query will display all the orders that contains the item as "1234".