DDL (Data Definition Language) : It is a set of SQL commands used to create, modify and delete database, structures but not data. These commands are normally not used by a general user, who should be accessing the database as every DDL command implicitly issues a COMMIT command to the database.
DML (Data Manipulation Language) : It is the area of SQL that allows changing data within the database.
DCL (Data Control Language) : It is the component of SQL statement that control access to data and to the database. Occasionally DCL statements are grouped with DML statements.
DQL (Data Query Language) : It is the component of SQL statement that allows getting data from the database and imposing ordering upon it. In includes the SELECT statement. This command is the heart of SQL. It allows getting the data out of the database perform operations with it. When a SELECT is fired against a table or tables the result is compiled into a further temporary table, which is displayed or perhaps received by the program i.e. a front end.
Examples of DDL, DML and DCL commands
DDL: Data Definition Language statements
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
GRANT Gives user's access priVileges to database
REVOKE Withdraw access privileges given with the GRANT command
DML: Data Manipulation Language statements
INSERT Insert data into a table
UPDATE Updates existing datawithin a table
DELETE Deletes all records from a table, the space for the records remain
CALL Call a PUS or Java subprogram
EXPLAIN PLAN Explain access path to data
LOCK TABLE Control concurrency
DCL: Data Control Language statements
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 what rollback segment to use,
GRANT / REVOKE Grant or take back permissions to or from the oracle users
DQL: Data Query Language statement
SELECT Retrieve data from the a database