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What is the difference between primary key, unique key, surrogate key?
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Kolta Sam- Member Since Jul-2011 | Jul 10th, 2011
Primary Key:
It is a visible key
It generated by user or application.
It could be changed by the user or application.
It could be queried
It used to form a relation between tables
It shouldn’t contain null value
It resemble table row
It is a unique identifier for a table object.
It contains only one key
It could contain numeric and strings characters.
It is an unique key which each row contain a distinct different key.
Example for it is a customer_Id.
It always starts by number one and second is two and so on but can starts with a different number.
Could created on one or more columns
No duplicate recordsSecondary Key:
It used to form a relation between tables.
It is alternate table key.
It used to search data with primary key
It could contains null value
It could contains more than one secondary key for each table
Created only on one columns
No duplicate records
It creates index clustered by default
Surrogate Key:It is invisible key for the user or the application.
It resembles database entity.
It generated by the system so it is invisible for user and application.
It shouldn’t contain null values
Only one surrogate key for each data entity
Its value is unique system wide.
Its value is never manipulated by the user or the application.
It never reused
It is frequently sequential number
It called synthetic key, an entity identifier, a system-generated key, a database sequence number, a factless key, a technical key, or an arbitrary unique identifier
No duplicate recordsgopi
- May 18th, 2018
Primary key not allow null values where as unique allows but both are alternates.
surrogate key serve as primery key in type 2 dimension tablesSukdya
- Nov 27th, 2017
Primary key doest not allow null values but unique key allows only one null value.
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What is the Difference between Replace and Translate
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Answered by: Saumendra Mohanty
- May 16th, 2006
Both Replace and Translate are single row functions in Oracle 9i.
The Replace Function replaces single character with multiple characters.
But in Translate Function replaces sinlge character with sinlge character only.
Manickavel
- Dec 26th, 2016
Translate is used for character by character substitution where as Replace is used for substituting a character with a word
shaikh siraj
- Apr 24th, 2016
String to string changing is called as replace.
Character to character changing is called as translate. -
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What is the difference between rownum,rowid
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rishipahuja- Member Since Aug-2006 | Aug 6th, 2006
rowid has a physical significance i.e you can read a row if you know rowid. It is complete physical address of a row.
While rownum is temporary serial number allocated to each returned row during query execution.
vinay
- Sep 20th, 2015
It it will be re-assigned to a different row when inserted by Oracle.
Arif
- Jul 3rd, 2015
I have one doubt like you said that rowid is automatically created when we add a row(record) then what happens to rowid
when we delete that record? -
Flow in Oracle Database.
What happens when a query is submitted in oracle? Please give the complete flow as to which all processes act and how the data is submitted / retrieved to / from the database .
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Table contain 2 columns like name and genderfor that i need output like this..countof female countofmale totalcountforeg 5 3 8
PK
- Feb 29th, 2012
There is one Oracle function ROLLUP, the same can be used for required output
QUERY:
SELECT GENDER,COUNT(GENDER)
FROM TABLE_NAME GROUP BY ROLLUP(GENDER);neelapu
- Apr 16th, 2010
SELECT COUNT(decode(sex1,'F',1)) "female count", COUNT(decode(sex1,'m',1)) "male count", COUNT(*) "total count" FROM
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Using which language oracle is developed?
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matabrez
- Nov 6th, 2010
Till 9i it was developed in using "C" and Java langauge. But from 10g it is fully developed in Java.
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Oracle Dbms Pipe Commands
Give the dbms_pipe commands in oracle of there execution,which are used to send & recieve messages what is the max size can sent at one go
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saginandkishore- Member Since Jun-2008 | Jun 24th, 2008
dbms_pipe is a IPC methodology which allows processes to communicate with each other using pipes.
The important functions/procedures in this package are
(1) CREATE_PIPE to create a new pipe
==> dbms_pipe.create_pipe(pipename) where pipename can be Oracle supplied or user defined as below
dbms_pipe.create_pipe(dbms_pipe.unique_session_name) -- Creates a PIPE based on your unique Session ID
or
pipename constant varchar2(100) := 'TEST_PIPE';
dbms_pipe.create_pipe(pipename);
(2) Having created the pipes try sending some data through the pipe. To send data prepare the data using dbms_pipe.pack_message(mesg_buf) where mesg_buf can be varchar2, char, number. Basically this procedure is overloaded for Numbers, Varchar2 and date. For long and raw data use the corresponding DBMS_PIPE.PACK_MESSAGE_RAW method. This procedure basically places the data into buffer which can be send on any pipe using the dbms_pipe.send_message(pipename) function.
(3) At the other end of the pipe you can receive the data using dbms_pipe.receive_message function. This functions fetches the data into buffer from where you can unpack the data using dbms_pipe.unpack_message function. This function gets the data in the buffer into a message buffer.
These are the basic commands that you can use for working with pipes. For more details visit oracle documentation.
imranbaig.geek
- Dec 1st, 2009
------Funtions------DBMS_PIPE.CREATE_PIPE:- for creating a pipeDBMS_PIPE.SEND_MESSAGE:- For sending messageDBMS_PIPE.REMOVE_PIPE:- for removing messageDBMS_PIPE.RECEIVE_MESSAGE:- For receiving message...
saginandkishore
- Jun 24th, 2008
dbms_pipe is a IPC methodology which allows processes to communicate with each other using pipes. The important functions/procedures in this package are(1) CREATE_PIPE to create a new pipe ==> dbms...
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What is the difference between cold backup and hot backup
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ttparavindh- Member Since Jun-2007 | Jun 19th, 2007
Cold Backup- We can take the Backup while DB(eg. Oracle) is down.
Hot Backup-We can take the Backup while DB(eg. Oracle) is running.
Cold backup is a physical backup. During a cold backup the database is closed and not available to users. All files of the database are copied (image copy). The datafiles do not change during the copy so the database is in sync upon restore.
Used when:Service level allows for some down time for backup
Hot backup is a physical backup. In a hot backup the database remains open and available to users. All files of the database are copied (image copy). There may be changes to the database as the copy is made and so all log files of changes being made during the backup must be saved too. Upon a restore, the changes in the log files are reapplied to bring the database in sync. Used when:A full backup of a database is needed
Service level allows no down time for the backupkrishnaprasad.sola
- Feb 9th, 2009
Cold Backup is possible only when the database is down means it is not available to users to access. Disadvantage is we effort downtime. Here we need to take backup of datafiles, control files, redo...
srk.srikanth
- Feb 8th, 2009
Cold Backup: Need to back up Database Files, Control Files, Online Redo Log files.Hot Backup: Need to back up Database Files, ControlFiles, Offline Redo Log files (archive files).
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Why do we need to use 'WHERE CURRENT OF' clause
saginandkishore
- Jun 24th, 2008
Where current of is used for updating the data referenced by cursor which was created as "SELECT FOR UPDATE".DECLARECURSROR MY_CURR IS SELECT COL1, COL2,...
shamkohli
- Jun 17th, 2008
While using cusor in PL/SQL, when we update a record, we can write WHERE CURRENT OF along with cursor_name.This is done in place of the where condition while updating. If we gi...
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