SQL | DDL, DML, DCL and TCL Commands

Structured Query Language(SQL) as we all know is the database language by the use of which we can perform certain operations on the existing database and also we can use this language to create a database. SQL uses certain commands like Create, Drop, Insert etc. to carry out the required tasks.

SQL commands are primarily grouped into four categories:

DDL(Data Definition Language)

DDL or Data Definition Language actually 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 database.

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

DML(Data Manipulation Language)

The SQL commands that deals with the manipulation of data present in database belong to DML or Data Manipulation Language and this includes most of the SQL statements.

SELECT – is used to retrieve data from the a database.
INSERT – is used to insert data into a table.
UPDATE – is used to update existing data within a table.
DELETE – is used to delete records from a database table.

DCL(Data Control Language)

DCL includes commands such as GRANT and REVOKE which mainly deals with the rights, permissions and other controls of the database system.

GRANT-gives user’s access privileges to database.
REVOKE-withdraw user’s access privileges given by using the GRANT command.

TCL(transaction Control Language) : TCL commands deals with the transaction within the database.

COMMIT– commits a Transaction.
ROLLBACK– rollbacks a transaction in case of any error occurs.
SAVEPOINT–sets a savepoint within a transaction.

References

https://www.postgresql.org/docs/current/ddl.html https://www.postgresql.org/docs/current/dml.html

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