Oracle Interview Questions and Answers for Freshers & Experienced Candidates
- Explain about Semijoin? and How to implement it in SQL?
A semi-join is an operation where the EXISTS clause is utilized with a subquery. It is called a semi-join because even if duplicate rows are returned in the subquery, the only one set of matching values in the outer query is returned. Moreover, it can be implemented utilizing WHERE EXISTS clause. - Explain the benefits of ORDBMS?
The language of the DBMS can be combined with an object-oriented programming language. The language may even be precisely the same as that utilized in the application, which does not confine the programmer to have two representations of his objects. - Explain what is NULL value in Oracle?
The NULL value represents missing or unknown data. It is utilized as a placeholder or represented it in as default entry to show that there is no actual data present. - Do you know how many memory layers are in the Oracle shared pool?
The Oracle shared pool includes two layers:
library cache
data dictionary cache - Explain the difference between Entity, Attribute, and Tuple?
Entity – A important thing about which data is needed. For example: EMPLOYEE (table).
Attribute – Something that defines the object. For example: empname, empno, empaddress.
Tuple: A row in a similarity is called Tuple. - What is a cursor? Why is cursor needed?
A cursor is a defined private SQL area from where the data can be passed and executed or accessed. The cursors are needed to process rows separately for queries returning numerous rows. - Explain about ALERT?
An alert is a window which seems in the center of the screen and covers a part of the current play. - What is meant by recursive hints in Oracle? And why it happens?
The amount of times a dictionary table is frequently called by multiple processes is known as a recursive hint. Although, it happens because of the small size of data dictionary cache. - Do you know what is PRAGMA?
PRAGMA is Oracle keyword to inform the compiler to do some special work.
Examples:-
PRAGMA AUTONOMOUS TRANSACTION
PRAGMA RESTRICT_REFERENCE - Explain what is the operation of HAVING clause?
The HAVING clause restricts the aggregated queries. After doing aggregation utilizing the GROUP BY clause, we can utilize the HAVING clause to append new conditions to the result. - What are different Oracle database objects?
TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES
