DQL: Data Query Language statements are used for performing queries on the data within schema objects.

List of DQL:
SELECT: It is used to retrieve data from the database.

DDL: Data Definition Language is a subset of SQL. It is a syntax for creating and modifying database objects such as tables, indices, and users.

List of DDL commands:
CREATE: This command is used to create the database or its objects (like table, index, function, views, store procedure, and triggers).
DROP: This command is used to delete objects from the database.
ALTER: This is used to alter the structure of the database.
TRUNCATE: This is used to remove all records from a table, including all spaces allocated for the records are removed.
COMMENT: This is used to add comments to the data dictionary.
RENAME: This is used to rename an object existing in the database.

DML: A data manipulation language is a computer programming language used for adding, deleting, and modifying data in a database.

List of DML commands:
INSERT: It is used to insert data into a table.
UPDATE: It is used to update existing data within a table.
DELETE: It is used to delete records from a database table.
LOCK: Table control concurrency.
CALL: Call a PL/SQL or JAVA subprogram.
EXPLAIN PLAN: It describes the access path to data.

DCL: Data Control Language includes commands such as GRANT and REVOKE which mainly deal with the rights, permissions, and other controls of the database system.

List of DCL commands:
GRANT: This command gives users access privileges to the database.
REVOKE: This command withdraws the user’s access privileges given by using the GRANT command.

TCL: Transaction Control Language commands are used to manage transactions in the database. These are used to manage the changes made by DML-statements. It also allows statements to be grouped together into logical transactions.

Examples of TCL commands:
COMMIT: Commit command is used to permanently save any transaction into the database.
ROLLBACK: This command restores the database to last committed state.
It is also used with savepoint command to jump to a savepoint in a transaction.
SAVEPOINT: Savepoint command is used to temporarily save a transaction so that you can rollback to that point whenever necessary.

SQL Interview Questions