SQL Categories

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 commands are mainly categorized into four categories as:

·         DDL - Data Definition Language.

·         DML - Data Modeling/Manipulation Language.

·         DCL - Data Control Language.

·         TCL - Transaction Control Language.

ü  DDL (Data Definition Language): It 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 the database.

Examples of DDL:

·       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.

·       RENAME – is used to rename an object existing in the database.

ü  DML (Data Manipulation Language): The SQL commands that deals with the manipulation of data present in the database belong to DML or Data Manipulation Language.

Examples of DML:

·         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.

Note: The SELECT statement is a limited form of DML statement in that it can only access data in the database. It cannot manipulate data in the database, although it can operate on the accessed data before returning the results of the query.

ü  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.

Examples of DCL:

·         GRANT - gives user’s access privileges to database.

·         REVOKE - withdraw user’s access privileges given by using the GRANT command.

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

Examples of TCL:

·         COMMIT – commits a Transaction.

·         ROLLBACK – rollbacks a transaction in case of any error occurs.

·         SAVEPOINT – sets a savepoint within a transaction.