Tamilnadu Samacheer Kalvi 12th Computer Science Notes Chapter 12 Structured Query Language (SQL) Notes

Structured Query Language (SQL):

  • The Structured Query Language (SQL) is a standard programming language to access and manipulate databases.
  • SQL allows the user to create, retrieve, alter, and transfer information among databases.
  • It is a language designed for managing and accessing data in a Relational Data Base Management System (RDBMS).

Relational Data Base Management System (RDBMS):

  • RDBMS is a type of DBMS with a row- based table structure that connects related data elements and includes functions related to Create, Read, Update and Delete operations, collectively known as CRUD.
  • Oracle, MySQL, MS SQL Server, IBM DB2 and Microsoft Access are RDBMS packages.

Different categories of SQL commands:

  • DDL – Data Definition Language
  • DML – Data Manipulation Language
  • DCL – Data Control Language
  • TCL – Transaction Control Language
  • DQL – Data Query Language

Data types used in SQL:

  • char (Character)
  • varchar
  • dec (Decimal)
  • Numeric
  • int (Integer)
  • Smallint
  • Float .
  • Real
  • double

Predetermined set of commands of SQL:
The SQL provides a predetermined set of commands like Keywords, Commands, Clauses and Arguments to work on databases.


  • They have a special meaning in SQL.
  • They are understood as instructions .

Commands :
They are instructions given by the user to the database also known as statements

They begin with a keyword and consist of keyword and argument

They are the values given to make the clause complete.

Data Definition Language:

  • The Data Definition Language (DDL) consist 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.

DDL commands:
i) Create ii) Alter iii) Drop iv) Truncate

  • Create : To create tables in the database.
  • Alter : The ALTER command is used
    to alter the table structure like adding a column, renaming the existing column, change the data type of any column or size of the column or delete the column from the table.
  • Drop : Delete tables from database.
  • Truncate : Remove all records from a table, also release the space occupied by those records.

Data Manipulation Language:
Data Manipulation Language (DML) is a computer programming language used for adding (inserting), removing (deleting), and modifying (updating) data in a database.

Basic types of DML:

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 is needed without specifying how to get it.

DML commands:

  • 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 (DCL):
Data Control Language (DCL) is a programming language used to control the access of data stored in a database.

DCL commands:

  • 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 (TCL):

  • 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.

TCL commands:
Commit: Saves any transaction into the database permanently.

  • Roll back: Restores the database to last commit state.
  • Save point: Temporarily save a transaction so that you can rollback.

Data Query Language (DQL):

  • The Data Query Language consist of commands used to query or retrieve data from a database.
  • One such SQL command in Data Query Language is “Select ” which is used to display the records from the table.

WAMP stands for “Windows, Apache, MySQL and PHP” It is often used for web development and internal testing, but may be also used to serve live websites.

Constraint is a condition,applicable on a field or set of fields or set of fields.

The different types of constraints are:

  1. Unique Constraint
  2. Primary Key Constraint
  3. Default Constraint
  4. Check Constraint
  5. Table Constraint

Samacheer Kalvi 12th Computer Science Notes