Question

What are the components of SQL? Write the commands in each.

Answer 1

Components of SQL:

The various components of SQL are

• Data Definition Language (DDL)
• Data Manipulation Language (DML)
• Data Query Language (DQL)
• Transactional Control Language (TCL)
• Data Control Language (DCL)

Data Definition Language (DDL):

• The Data Definition Language (DDL) consists of SQL statements used to define the database structure or schema.
• It simply deals with descriptions of the database schema and is used to create and modify the structure of database objects in databases.
• The DDL provides a set of definitions to specify the storage structure and access methods used by the database system.

A DDL performs the following functions:

• It should identify the type of data division such as data item, segment, record, and database file.
• It gives a unique name to each data item type, record type, file type, and database.
• It should specify the proper data type.
• It should define the size of the data item.
• It may define the range of values that a data item may use.
• It may specify privacy locks for preventing unauthorized data entry.

SQL commands which come under Data Definition Language are:

Create	To create tables in the database.
Alter	Alters the structure of the database.
Drop	Delete tables from the database.
Truncate	Remove all records from a table, also release the space occupied by those records.

Data Manipulation Language:

• A Data Manipulation Language (DML) is a computer programming language used for adding (inserting), removing (deleting), and modifying (updating) data in a database.
• In SQL, the data manipulation language comprises the SQL-data change statements, which modify stored data but not the schema of the database table.
• After the database schema has been specified and the database has been created, the data can be manipulated using a set of procedures that are expressed by DML.

The DML is basically of two types:

• Procedural DML – Requires a user to specify what data is needed and how to get it.
• Non-Procedural DML – Requires a user to specify what data are needed without specifying how to get it.

SQL commands which come under Data Manipulation Language are:

Insert	Inserts data into a table
Update	Updates the existing data within a table
Delete	Deletes all records from a table, but not the space occupied by them.

Data Control Language:

• A Data Control Language (DCL) is a programming language used to control the access of data stored in a database.
• It is used for controlling privileges in the database (Authorization).
• The privileges are required for performing all the database operations such as creating sequences, views of tables, etc.

SQL commands which come under Data Control Language are:

Grant	Grants permission to one or more users to perform specific tasks.
Revoke	Withdraws the access permission given by the GRANT statement.

Transactional Control Language:

• Transactional control language (TCL) commands are used to manage transactions in the database.
• These are used to manage the changes made to the data in a table by DML statements.

SQL command which comes under Transfer Control Language are:

Commit	Saves any transaction into the database permanently.
Rollback	Restores the database to the last commit state.
Savepoint	Temporarily save a transaction so that you can roll back.

Data Query Language:
The Data Query Language consists of commands used to query or retrieve data from a database.
One such SQL command in Data Query Language is
Select: It displays the records from the table.