Structured Query Language (SQL), as we are all aware, is a database language that we can use to construct new databases and execute specific actions on those that already exist.
These SQL commands are mainly categorized into five categories:
DDL – Data Definition Language
DQL – Data Query Language
DML – Data Manipulation Language
DCL – Data Control Language
TCL – Transaction Control Language
DDL (Data Definition Language)
DDL consists of the SQL commands that can be used to define the database schema. It simply deals with descriptions of the database schema and is used to create and modify the structure of database objects in the database.
DDL is a set of SQL commands used to create, modify, and delete database structures but not data.
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.
DQL (Data Query Language)
DQL statements are used for performing queries on the data within schema objects. The purpose of the DQL Command is to get some schema relation based on the query passed to it.
List of DQL:
SELECT: It is used to retrieve data from the database.
DML(Data Manipulation Language)
The majority of SQL statements are part of the DML, or Data Manipulation Language, which is used to manipulate data that is present in databases.
It is the part of the SQL statement controls access to data and to the database. Essentially, DML statements and DCL statements belong together.
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)
DCL 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)
Transactions group a set of tasks into a single execution unit. Each transaction begins with a specific task and ends when all the tasks in the group successfully complete. If any of the tasks fail, the transaction fails. Therefore, a transaction has only two results: success or failure.
TCL commands are used to control the execution of a transaction:
List of TCL commands:
BEGIN: Opens a Transaction.
COMMIT: Commits a Transaction.
ROLLBACK: Rollbacks a transaction in case of any error occurs.
SAVEPOINT: Sets a save point within a transaction.