Best oracle sql interview questions:Part 1

Best oracle sql interview questions:

1 What is Oracle table?


Answer:


A table is the object for data storage in an Oracle database.


Table has rows and columns.





2. What are Clusters?


Answer:


Clusters are collections of one or more tables that are frequently used in tandem and are physically stored together to share common columns.


3. Describe an index.


Answer:an index is an optional structure that can be added to a table to provide direct access to rows. A table's one or more columns may have an index defined for it.


4. What benefits can views offer? Answer:


To add an extra layer of protection to a table, limit access to a predefined subset of the database's rows and columns.


Cover up complex data.


Make user commands simpler.


Display the information from a viewpoint distinct from the one found in the base table.


Save intricate queries.


5. What are the various types of queries?


Answer:


The types of queries are :


Normal Queries


Sub Queries


Co-related queries


Nested queries


Compound queries


6. how many types of joins are there in the market?


Answer:


inner joins


left outer joins


right outer joins


full outer joins


cross joins


self join


7: What is SQL? Explain its significance in the context of Oracle databases.


Answer: SQL, or Structured Query Language, is a standardized programming language used for managing and manipulating relational databases.


In the context of Oracle databases, SQL plays a pivotal role in performing tasks such as querying data, modifying table structures, and controlling


access to the database. With SQL, users can interact with Oracle databases seamlessly, making it an indispensable tool for database administrators, developers, and analysts.


8: Differentiate between SQL and PL/SQL. Provide examples to illustrate the distinction.


Answer: SQL (Structured Query Language) is a declarative language used for querying and manipulating data in relational databases.


PL/SQL (Procedural Language/Structured Query Language), on the other hand, is a procedural extension of SQL that allows users to write procedural


code within SQL statements.


sql


-- Example of SQL Query


SELECT * FROM employees WHERE department = 'CS';


-- Example of PL/SQL Procedure


CREATE OR REPLACE PROCEDURE calculate_salary_bonus (employee_id IN NUMBER) IS


bonus_amount NUMBER;


BEGIN


-- Calculate bonus based on employee performance


-- Code logic goes here


END;


9: What are the different types of joins in SQL? Provide a real-world scenario for each type.


Answer: There are several types of joins in SQL, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.


sql


-- Example of INNER JOIN


SELECT employees.employee_id, departments.department_name


FROM employees


INNER JOIN departments ON employees.department_id = departments.department_id;


-- Example of LEFT JOIN


SELECT customers.customer_name, orders.order_id


FROM customers


LEFT JOIN orders ON customers.customer_id = orders.customer_id;


10. Describe the idea of SQL subqueries. Give a real-world example to demonstrate how to use it?


Answer:A subquery is a SQL query that is nested inside another SQL query. It is Used as an inner query.


It enables users to get data according to the parameters given in the outer query.


sql


Example 1:


select


(select ood.organization_code from apps.org_organization_definition ood where ood.inventory_item_id= msi.inventory_item_id


and ood.organization_id=msi.organization_id) "organization_code",


msi.description





from mtl_system_items msi;


-- Example 2 of Subquery


SELECT employee_id, last_name, job_id


FROM employees


WHERE department_id IN (SELECT department_id FROM departments WHERE department_name = 'IT');


11: What are the advantages of using indexes in Oracle databases? Provide examples to demonstrate their impact on query performance.


Answer: In databases, indexes are data structures that speed up data retrieval processes.


They allow for faster access to rows in a table by creating a sorted list of key values.


sql


-- Example of Creating an Index


CREATE INDEX emp_name_idx ON employees(last_name);


-- Example of Using an Index in a Query


SELECT * FROM employees WHERE last_name = 'Smith';