Question

If the following appeared in a CREATE TABLE statement FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) true false - The jable bong crealed must have a column named PeolD true false -The CREATE TABLEWill fail becaue2 tables can ut have a field with the named PersonlD true false -personlD in thi table must be UNIQUE true false- There must be a diftorent table named Pasons Deviousl reated Record Answer

Answer 1

A foreign key is used to connect two tables.The foreign key in one table references the primary key of the another table( some case it can refer the primary key of the same table also).The table containing the primary key is parent and table containg the foreign key is child table.

FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

First PersonID is the foreign key column in the child table and Persons is the parent table .Persons(PersonID) indicates the primary key of parent table.

eg.CREATE TABLE Order (
    Oid int NOT NULL,
    Ono int NOT NULL,
    PersonID int,
    PRIMARY KEY (Oid),
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);

The value of the foreign key either one of the value present in the parents tables primary column or it can be null.

1. The table being created must have a column named personid

True

2. The create table will fail because 2 tables can not have a field with the named personid

False

3. personid in this table must be unique.

false

foreignkey need not be unique.the only constraint is it must have value that is either present in parent table or it can be null.

4. There must be a different table named persons previously created

True

Since we are creating a link ,the parent table must be present before creating the foreign key references.