Oracle
Interview Questions
Oracle is a secured
database that is widely used in multinational companies. The frequently asked
questions from oracle database are given below.
1) What are the components of physical database
structure of Oracle database?
Components of physical
database structure are given below.
- One or more data files.
- Two or more redo log files.
- One or more control files.
2) What are the components of logical database
structure in Oracle database?
Components of logical
database structure.
- Tablespaces
- Database's schema objects
3) What is a tablespace?
A database contains Logical
Storage Unit called tablespaces. A tablespace is a set of related logical
structures. Actually a tablespace groups related logical structures together.
4) What is a SYSTEM tablespace and when it is
created?
When the database is
created in Oracle database system, it automatically generate a SYSTEM named
SYSTEM tablespace. The SYSTEM tablespace contains data dictionary tables for
the entire database.
5) What is an Oracle table?
A table is basic unit of
data storage in Oracle database. A table contains all the accessible
information of a user in rows and columns.
6) In the Oracle version 9.3.0.5.0, what does
each number shows?
Oracle version number
refers:
- 9 - Major database release number
- 3 - Database maintenance release
number
- 0 - Application server release
number
- 5 - Component Specific release
number
- 0 - Platform Specific release
number
7) What is bulk copy or BCP in Oracle?
Bulk copy or BCP in Oracle,
is used to import or export data from tables and views but it does not copy
structure of same data.
The main advantage of BCP
is fast mechanism for coping data and you can also take the backup of data
easily.
8) What is the relationship among database,
tablespace and data file?
An Oracle database contains
one or more logical storage units called tablespaces. These tablespaces
collectively store whole data of databases and each tablespace in Oracle
database consists of one or more files called datafiles. These datafiles are
physical structure that confirm with the operating system in which Oracle is
running.
9) What is a snapshot in Oracle database?
A snapshot is a replica of
a target master table from a single point-in-time. In simple words you can say,
snapshot is a copy of a table on a remote database.
10) What is the difference between hot backup
and cold backup in Oracle? Tell about their benefits also.
Hot
backup (Online Backup): A hot
backup is also known as online backup because it is done while the database is
active. Some sites can not shut down their database while making a backup copy,
they are used for 24 hour a day, 7 days a week.
Cold
backup (Offline Backup): A cold
backup is also known as offline backup because it is done while the database
has been shutdown using the SHUTDOWN normal command. If the database is
suddenly shutdown with a uncertain condition it should be restarted with
RESTRICT mode and then shutdown with NORMAL option.
For a complete cold backup
the following files must be backed up.
All datafiles, All control
files, All online redo log files(optional) and the init.ora file (you can
recreate it manually).
11) How many memory layers are in the Oracle
shared pool?
Oracle shared pools
contains two layers:
1. library
cache
2. data
dictionary cache
12) What is save point in Oracle database?
Save points are used to
divide a transaction into smaller parts. It allows rolling back of a
transaction. Maximum five save points are allowed. It is used to save our data,
whenever you encounter an error you can roll back from the point where you save
your SAVEPOINT.
13) What is hash cluster in Oracle?
Hash cluster is a technique
to store a data in hash table and improve the performance of data retrieval.
Hash function is applied on table row's cluster key value and store in hash
cluster.
14) What are the various Oracle database
objects?
Tables: This is
a set of elements organized in vertical and horizontal fashion.
Tablespaces: This is
a logical storage unit in Oracle.
Views: It is
virtual table derived from one or more tables.
Indexes: This is
a performance tuning method to process the records.
Synonyms: This is
a name for tables.
15) What is the difference between pre-select
and pre-query?
A pre-query trigger fire
before the query executes and fire once while you try to query. With the help
of this trigger you can modify the where clause part dynamically.
Pre-select query fires
during the execute query and count query processing after Oracle forms
construct the select statement to be issued, but before the statement is
actually issued.
Pre-query trigger fires
before Pre-select trigger.
16) How to convert a date to char in Oracle?
Give one example.
The to_char() function is used
to convert date to character. You can also specify the format in which you want
output.
1. SELECT to_char ( to_date ('12-12-2012', 'DD-MM-YYYY') , 'YYYY-MM-DD') FROM dual;
Or,
1. SELECT to_char ( to_date ('12-12-2012', 'DD-MM-YYYY') , 'DD-MM-YYYY') FROM dual;
17) What are the extensions used by Oracle
reports?
Oracle reports are use to
make business enable with the facility to provide information of all level
within or outside in a secure way. Oracle report uses REP files and RDF file
extensions.
18) How to convert a string to a date in
Oracle database?
Syntax: to_date (string ,
format)
Let us take an example :
1. to_date ('2012-12-12', 'YYYY/MM/DD')
It will return December 12, 2012.
19) How do you find current date and time in
Oracle?
The SYSDATE() function is used
in Oracle to find the current date and time of operating system on which the
database is running.
1. SELECT TO_CHAR (SYSDATE, 'MM-DD-YYYY HH24:MI:SS') "Current_Date" FROM DUAL;
20) What will be the syntax to find current
date and time in format "YYYY-MM-DD"?
1. SELECT TO_CHAR (SYSDATE, 'YYYY-MM-DD HH24:MI:SS') "Current_Date" FROM DUAL;
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