Difference between DDL, DML and DCL commands Posted by MOHAMMED ABDUL HAMEED on 11:40 PM

DDL

Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:

• CREATE - to create objects in the database
• ALTER - alters the structure of the database
• DROP - delete objects from the database
• TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
• COMMENT - add comments to the data dictionary
• RENAME - rename an object

DML

Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:

• SELECT - retrieve data from the a database
• INSERT - insert data into a table
• UPDATE - updates existing data within a table
• DELETE - deletes all records from a table, the space for the records remain
• MERGE - UPSERT operation (insert or update)
• CALL - call a PL/SQL or Java subprogram
• EXPLAIN PLAN - explain access path to data
• LOCK TABLE - control concurrency

DCL

Data Control Language (DCL) statements. Some examples:

• GRANT - gives user's access privileges to database
• REVOKE - withdraw access privileges given with the GRANT command

TCL

Transaction Control (TCL) statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.

• COMMIT - save work done
• SAVEPOINT - identify a point in a transaction to which you can later roll back
• ROLLBACK - restore database to original since the last COMMIT
• SET TRANSACTION - Change transaction options like isolation level and what rollback segment to use

Environment Variable for Oracle Database Posted by MOHAMMED ABDUL HAMEED on 12:28 AM

How to check if ORACLE_HOME is set already?


To check specific environment variable set:
$ echo $ORACLE_HOME

To check all the environment variables set:

$ env

On Windows Systems:

To check specific environment variable set:

C:\> set ORACLE_HOME

OR

C:\echo %ORACLE_HOME%

To check all the environment variables set:

C:\> set

Or

C:\> env

Other way, to check the ORACLE_HOME, is as follows.
Start -> Run -> Regedit (enter) -> HKEY_LOCAL_MACHINE -> SOFTWARE –> ORACLE

i.e. My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE

How to check using sqlplus command:
To find the ORACLE_HOME path in Oracle Database

How to set the ORACLE_HOME environment variable?
On Unix/Linux Systems:

Define the ORACLE_HOME value in the user profile file i.e. .bash_profile or .profile

ORACLE_HOME=$ORACLE_BASE/product/10.2.0
export ORACLE_HOME

On Windows Systems:

My Computer -> Properties -> Advanced -> Environment Variables -> System Variables -> New/Edit/Delete (to set the variables)

After setting the environment variables as above, open a fresh CMD tool and check whether they set properly or not. Do not try on already opened CMD tool to make sure the variables set or not.

Another way to physically set the variables as follow at the DOS prompt:

C:\> set ORACLE_HOME=C:\oracle\app\product\10.2.0
C:\> echo %ORACLE_HOME%

Linux 

export ORACLE_SID=COREDB
export ORACLE_HOME=/u01/home/app/product/11.2.0/dbhome_1
export PATH=$ORACLE_HOME/bin:$PATH: