Structured Query Language
Overview
- What is Structured Query Language?
- Data Definition Language
- Data Query Language
- Data Manipulation Language
- Data Control Language
- Transaction Control Language
What is Structured Query Language?
- Structured Query Language (SQL) is the database language used to create and perform operations on databases.
- SQL uses certain commands like
CREATE, INSERT, SELECT, DROP, etc. to carry out the required tasks.
- SQL commands are mainly categorized into four categories as:
- DDL – Data Definition Language
- DQL – Data Query Language
- DML – Data Manipulation Language
- DCL – Data Control Language
- TCL – Transaction Control Language
Data Definition Language
- Data Definition Language (DDL) consists of the SQL commands used to define the database schema.
- It deals with descriptions of the database schema
- It is used to create and modify the structure of database objects in the database.
- Example
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.
Data Query Language
- DML statements are used for performing queries on the data within schema objects.
- The purpose of Data Query Language (DQL) is to get some schema relation based on the query passed to it.
- Example of DQL
SELECT– is used to retrieve data from the a database.
Data Manipulation Language
- The SQL commands that deals with the manipulation of data present in the database belong to Data Manipulation Language (DML) and this includes most of the SQL statements.
- 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.
Data Control Language
- 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 commands:
GRANT - gives user’s access privileges to database.REVOKE - withdraw user’s access privileges given by using the GRANT command.
Transaction Control Language
- Transaction Control Language (TCL) commands deal with the transaction within the database.
- Examples of TCL commands:
COMMIT - commits a Transaction.ROLLBACK – rollbacks a transaction in case of any error occurs.SAVEPOINT – sets a savepoint within a transaction.SET TRANSACTION – specifies characteristics of the transaction.