Structured Query Language(SQL) is the database language to perform certain operations on the database.
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 or Data Definition Language actually consists of the SQL commands that can be used to define the database schema. 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.
SELECT: It is used to retrieve data from the database.
DML (Data Manipulation Language)
The SQL commands that deal with the manipulation of data present in the database belong to DML or Data Manipulation Language and this includes most of the SQL statements.
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.
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.
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