Oracle Questions

Q:

Explain Row level and statement level trigger.

Answer

Row Level Trigger :
Row Level Trigger is fired each time row is affected by Insert, Update or Delete command. If statement doesn’t affect any row, no trigger action happens.

Statement Level Trigger :
This kind of trigger fires when a SQL statement affects the rows of the table. The trigger activates and performs its activity irrespective of number of rows affected due to SQL statement.

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Subject: Oracle - Technology

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Q:

What is WATER MARK in oracle? Explain the significance of High water mark.

Answer

WATER MARK is a divided segment of used and free blocks. Blocks which are below high WATER MARK i.e. used blocks, have at least once contained some data. This data might have been deleted later. Oracle knows that blocks beyond high WATER MARK don’t have data; it only reads blocks up to the high WATER MARK during a full table scan. 

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Subject: Oracle - Technology

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Q:

What do you mean by a deadlock?

Answer

 - When two processes are waiting to update the rows of a table which are locked by another process, the situation is called a deadlock.
 - The reasons for it to happen are:
 * lack of proper row lock commands.
 * Poor design of front-end application
- It reduces the performance of the server severely.
- These locks get automatically released automatically when a commit/rollback operation is performed or any process is killed externally.

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Subject: Oracle - Technology

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Q:

What is a shared pool?

Answer

Shared pool in oracle contains cache information that collects, parses, interprets and executes SQL statements that goes against database. This shared pool acts like a buffer for these SQL statements.

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Subject: Oracle - Technology

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Q:

What is Control File used for?

Answer

Control File is used for:
- Database recovery.
- Whenever an instance of an ORACLE database begins, its control file is used to identify the database and redo log files that must be opened for database operation to go ahead.

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Subject: Oracle - Technology

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Q:

A data warehouse is composed of

A) current data B) internal and external data sources
C) historical data from legacy systems D) historical & current data
 
Answer & Explanation Answer: C) historical data from legacy systems

Explanation:

A data warehouse is a relational database that is designed for query and analysis rather than transaction processing. It usually contains historical data that is derived from transaction data, but it can include data from other sources. Data warehouses are designed to help you analyze your data.

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Q:

What is a PL/SQL package? what are its Advantages ?

Answer

A package is a collection of related PL/SQL objects. The package contains a body and a specification. The package specification has the declaration which is public and can be used in the PL/SQL sub programs inside the package.


The package body holds the implementation of all the PL/SQL objects declared in the specification.


Example of a PL/SQL Package.


CREATE OR REPLACE PACKAGE emp_data AS 


PROCEDURE add_employee (


      ename VARCHAR2,


      job VARCHAR2,


      mgr NUMBER,


      sal NUMBER,


      deptno NUMBER);


END emp_actions;


 


CREATE OR REPLACE PACKAGE BODY emp_data AS 


PROCEDURE add_employee (


       ename VARCHAR2,


       job VARCHAR2,


       mgr NUMBER,


       sal NUMBER,


       deptno NUMBER) IS


BEGIN


         INSERT INTO emp VALUES (empno_seq.NEXTVAL, ename, job, mgr, SYSDATE, comm, deptno);


END add_employee;


END emp_data;


Advantages of  PL/SQL packages :


Packages are easier for application designing, encapsulating data, additional functionality and better performance. An application has various modules which can be placed in packages and handled easier.


 

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Subject: Oracle - Technology

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Q:

What is personal oracle lite?

Answer

Personal Oracle lite is single user database for distributed and mobile computing. It supports a full range of Java database features as well as advanced replication. Or in other words it is Oracle's lightweight, fully-functional, single-user object- relational database. A small, zero administration embedded database.


Some of the features supported:


- Java Support


- Java Store Procedure Support


- Java triggers Supported


- Multi-column indexing and outer joins.


- Easy to use graphical user interface


- Supports both object and relational database models


- Simultaneous viewing of classes and relational tables

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