Which of the following statements is false with respect to relati
A. Foreign key constraints are referential integrity constraints.
B. Nulls reduce space requirements in tables.
C. A primary key uniquely identifies a row in a table.
D. A disadvantage of highly normalized tables is that queries may require too many time consuming joins.
Please scroll down to see the correct answer and solution guide.
Right Answer is: B
SOLUTION
Concept:
RDBMS stands for a relational database management system. A relational database is made up of a number of relations and corresponding relational database schema. RDBMS data is in the form of tables, records.
Explanation:
Consider the statements one by one :
1) Foreign key constraints are referential integrity constraints.
It is correct. The foreign key in a table refers to the primary key of another table. That is the reason foreign key constraints are referential integrity constraints. Foreign keys contain the attribute values equal or a subset as that or the primary key.
2)Nulls reduce space requirements in tables.
It is incorrect. Null does not reduce space in tables. When we apply the count function in a table, then it also counts the tuple having NULL value.
3) A primary key uniquely identifies a row in a table.
This statement is correct. A primary key helps in uniquely identifying a row in table. As attribute which is the primary key does not contain any duplicate values and also primary key value can not be NULL.
4)A disadvantage of highly normalized tables is that queries may require too many time consuming joins.
The given statement is correct. Highly normalized tables have time-consuming joins. Because it totally depends on the query, sometimes queries are too large such that the join operation will too much time to normalize the tables.