Database [3i Infotech Placement]: Sample Questions 197 - 199 of 294

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Question 197

Database

Question

MCQ▾

ENQUEUE resources parameter information is derived from … .

Choices

Choice (4)

a.

LOG_BUFFER

b.

DB_BLOCK_SIZE

c.

Processes or DDL_LOCKS and DML_LOCKS

d.

Question does not provide sufficient data or is vague

Answer

c.

Explanation

Two Types of Locks

  1. DML lock
  2. DDL lock
Two Types of Locks
  • The dba_dml_locks and dba_ddl_locks views are both created by the catblock. sql script and are used to monitor DML and DDL locks
  • Parameter information is derived from Processes or DDL_LOCKS and DML_LOCKS.
  • Sets the number of resources it can be lock concurrently by the lock manager.
  • Oracle allocates the number of enqueuse specified by the ENQUEUE_RESOURCES parameter, at database startup time.
  • If we explicit set ENQUEUE_RESOURCES to a value higher than DML_LOCK, then oracle uses the value we provide.

Question 198

Database
Edit

Write in Short

Short Answer▾

What does the following query do?

SELECT SAL + NVL (COMM, 0) FROM EMP.

Explanation

  • This displays the total salary of all employees.
  • Null values in the commission column [NVL (COMM, 0) ] will replaced by 0 and added to salary.

Question 199

Database
Edit

Write in Short

Short Answer▾

What is a view? How it is related to data independence?

Explanation

  • A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table.
  • In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
  • Growth and restructuring of base tables is not reflected in views.
  • Thus the view can insulate users from the effects of restructuring and growth in the database.
  • Hence accounts for logical data independence.

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