What are the difference between DDL, DML and DCL commands ?

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

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