Oracle Questions

Q:

What strategies are available for backing-up an Oracle database?

Answer

The backup strategies that are provided by Oracle are as follows:


- Logical backup using Exports and import.


- Physical file system backup


- RMAN Recovery Manger which is also known as incremental files system backup.

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Subject: Oracle - Technology

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Q:

How can we call DDL statements like CREATE, DROP, TRUNCATE, etc. from PL/SQL?

Answer

EXECUTE IMMEDIATE command can be used to call DDL statements. 


Example:


BEGIN


EXECUTE IMMEDIATE  'TRUNCATE TABLE employee';


END;

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Subject: Oracle - Technology

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Q:

What is LINQ ?

Answer

LINQ stands for " Language Integrated Query " and it is pronounced as "LINK".
LINQ was introduced in with .NET framework 3.5 including VS2008. It enables you to query the data from various data source like SQL, XML document, ADO .NET data source, web services and any other objects such as Collection, Generics etc...

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Q:

What is RAC and how is it different from non RAC databases?

Answer

Oracle Real Application Clusters (RAC) is a software component we can add to a high-availability solution that enables users on multiple machines to access a single database with increased performance. RAC comprises two or more Oracle database instances running on two or more clustered machines and accessing a shared storage device via cluster technology. To support this architecture, the machines that host the database instances are linked by a high-speed interconnect to form the cluster. Oracle RAC offers features in the following areas:


- Scalability


- Availability


- Load balancing


- Failover

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Subject: Oracle - Technology

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Q:

Define cursor attributes: %FOUND, %NOTFOUND, %ROWCOUNT, and %ISOPEN

Answer

- %FOUND


 This is a Boolean variable which evaluates to TRUE if the last row is successfully fetched.


 


- %NOTFOUND


 This is a Boolean variable which evaluates to TRUE if the last row is not successfully fetched. This means there are no more rows to fetch.


 


- %ROWCOUNT


 Returns the number of rows fetched by the cursor.


 


- %ISOPEN


If the cursor is open, it evaluates to TRUE else FALSE.

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Subject: Oracle - Technology

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Q:

Oracle Server supports two different forms of replication: Basic and Advanced replication. Explain difference between these.

Answer

Basic Replication : Basic replication is implemented using standard CREATE SNAPSHOT or CREATE MATERIALIZED VIEW statements. It can only replicate data and not procedures, indexes replication is always one-way, and snapshot copies are read only.


Advanced Replication : Advanced replication supports various configurations of updatable snapshot, multi-master and update anywhere replication. It is more difficult to configure but allows data and other database objects like indexes and procedures to be replicated.


 


Differences between Basic and Advanced replications:


- With basic replication, data replicas provide read-only access to the table data whereas advanced replication features extend the capabilities of basic read-only replication by allowing applications to update table replicas throughout a replicated database system.


- With Basic Replication applications can query data from local data replicas. On the other hand with advanced replication, data replicas anywhere in the system can provide both read and update access to a table's data.

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Q:

Explain how to start and stop the Oracle HTTP Server.

Answer

Oracle HTTP Server is managed by OPMN which stands for Oracle Process Manager and Notification Server. With the use of opmnctl utility we can start, stop and restart Oracle HTTP Server. If we don’t use this utility the configuration management infrastructure cannot detect or communicate with the Oracle HTTP Server processes, and problems may occur.


The startproc command for the case of Windows is: ORACLE_HOME\opmn\bin> opmnctl [verbose] startproc ias-component=HTTP_Server.


To stop Oracle HTTP Server, use the stopproc command: Windows: ORACLE_HOME\opmn\bin> opmnctl [verbose] stopproc ias-component=HTTP_Server.

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Q:

Explain some of the commonly used Predefined PL/SQL Exceptions.

Answer

1)Divide by zero        – This is raised when any number is attempted to divide by zero.


2)TOO MANY ROWS   - A SELECT INTO statement returns more than one row.


3)CASE_NOT_FOUND - No choice in the WHEN clause of a case statement is selected.


4)LOGIN_DENIED      - An attempt to login with an invalid username or password.


5)PROGRAM_ERROR  - An internal PL/SQL problem.

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