Database [3i Infotech Placement]: Sample Questions 56 - 58 of 294

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Question 56

Database
Edit

Write in Short

Short Answer▾

What is 3NF?

Explanation

  • A relation schema R is in 3NF if it is in 2NF and every FD X A either of the following is true
  • X is a Super-key of R
  • A is a prime attribute of R
  • In other words, if every non prime attribute is non-transitively dependency on primary key.

Question 57

Database

Question

MCQ▾

Does the database trigger fire when the table is TRUNCATED?

Choices

Choice (4)

a.

Yes

b.

No

c.

All of the above

d.

None of the above

Answer

b.

Explanation

Define Truncating a Table
  • No, the database trigger does not fire when the table is TRUNCATED- Because, we cannot trigger on truncate operation.
  • Database trigger apply only for INSERT/UPDATE/DELETE.

Truncate Statement

  • Use TRUNCATE TABLE statement to remove all rows from a table.
  • Removing rows with the TRUNCATE TABLE can be more efficient than dropping and re-creating a table.
  • Performs the same function as DELETE statement without a WHERE clause.

Question 58

Database
Edit

Describe in Detail

Essay▾

What is join dependency and inclusion dependency?

Explanation

Join Dependency

  • When we decompose table those decomposed table should satisfy join dependency.
  • Dependency is generalization of multivalued dependency.
  • A is said to hold over a relation R if is a lossless-join decomposition of R .
  • No set of sound and complete inference rules exist for JD.
  • Important in connection with the decomposition technique for schema design and normalization.
  • Decomposition technique avoids redundancies due to data dependencies by decomposing a relation into smaller parts.

Example:

Understanding Example of Join Dependency (JD)

Inclusion Dependency

Define Inclusion Dependencies
  • A statement of the form that some columns of a relation are contained in other columns.
  • A foreign key constraint is an example of inclusion dependency.
  • Defined in order to formalize two types of inter relational constraints:
    • The foreign key constraint cannot be specified as a functional or multi valued dependency because it relates attributes across relations.
    • Constraint between two relations that represent a class or a subclass relationship also it has no formal definition in terms of the functional , multi valued, and join dependencies.

Example of Inclusion dependencies:

Example of Inclusion Dependencies

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