Question

QUESTION 6 Which of the following statements best illustrates the "Key" constraint? The schema MUST be created before tables are added A primary key MUST NOT have duplicate values A foreign key value MUST have a value already present as a primary key in another table (or be NULL) A primary key value MUST have a value QUESTION 7 Which of the following statements best illustrates the "Referential Integrity" constraint? The schema MUST be created before tables are added A foreign key value MUST have a value already present as a primary key in another table (or be NULL) A primary key value MUST have a value A primary key MUST NOT have duplicate values

Answer 1

6

Ans: A primary key MUST NOT have duplicate values

In databases mainly we have 2 Types of keys

1. Primary key:

A key should be unique throughout the table and it should not have null values. It is used to uniquely identify the table row or one unique record of table.

2. Foreign key:

A key which is referring to the primary key of another table.

A foreign key has link with the primary key of another table.

7

Ans: a foreign key key value MUST have a value already present as a primary key in another table( or be null)

Referential integrity means having a link with another primary key of another table and if that primary key data changes automatically it will be affected.

A foreign key have a reference of primary key