Database - Logical Database Design - Discussion

Discussion :: Logical Database Design - General Questions (Q.No.1)


The entity integrity rule states that:

[A]. no primary key attribute may be null.
[B]. no primary key can be composite.
[C]. no primary key may be unique.
[D]. no primary key may be equal to a value in a foreign key.

Answer: Option A


No answer description available for this question.

Priyank said: (Jan 2, 2012)  
In the relational data model, entity integrity is one of the three inherent integrity rules. Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not null. A direct consequence of this integrity rule is that duplicate rows are forbidden in a table. If each value of a primary key must be unique no duplicate rows can logically appear in a table. The NOT NULL characteristic of a primary key ensures that its value can be used to identify all rows in a table.

Bhargav.K said: (Jun 7, 2014)  
Primary key is also satisfies the unique key. Unique key allows the null values but not the duplicate values.

Prashant said: (Aug 21, 2016)  
A table can have unique column value other than the primary key, and for that concept, option C may be correct.

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