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

Database Command Types

DDL

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

-          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 in database. DML commands are not auto-committed. It means changes made by DML command are not permanent to database, it can be rolled back.

-          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

-          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 Language (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